M250 - Object-Oriented Java Programming

Front 1

absolute pathname

Back 1

A full path to a file beginning from the name of the storage device.

Front 2

abstract class

Back 2

A class that defines a common message protocol and common set of instancevariables for its subclasses. In Java an abstract class cannot be instantiated.

Front 3

abstract method

Back 3

A method declared as abstract. Abstract methods have no bodies. Theymust be implemented in any concrete subclasses of the class in which they arespecified. Interfaces also specify abstract methods, which must beimplemented by classes implementing the interface.

Front 4

access level

Back 4

The scope for access that exists for a software component such as a method.There are four access levels in Java: public, private, protected anddefault. The default level occurs when no access modifier is specified.

Front 5

access modifier

Back 5

One of three Java keywords (public, private, protected) which specifythe visibility of variables and methods.

Front 6

accessor message

Back 6

Another name for a getter message.

Front 7

accessor method

Back 7

Another name for a getter method.

Front 8

actual argument

Back 8

An actual argument is a value used in a message that is copied to a formalargument for use inside the corresponding method. Actual arguments must beof a compatible type with their corresponding formal arguments.

Front 9

annotation

Back 9

An annotation is a piece of code in a source file that indicates a programmer’sintention to the compiler. The only annotation we use in M250 is @Override.All annotations begin with the character @ in Java.

Front 10

array

Back 10

An indexable, fixed-size collection whose elements are all of the same type.

Front 11

array initialiser

Back 11

An expression that can be used to initialise an array using assignment, ashortcut way of initialising array elements

Front 12

assert

Back 12

The keyword in a Java assertion statement used to indicate a condition thatshould be true in order for the code to be correct, particularly used inprivate methods.

Front 13

assertion

Back 13

A statement in the Java language that enables you to test your assumptionsabout your program; a condition that a programmer believes should be true.

Front 14

assignment

Back 14

Assignment is the process that results in the variable on the left-hand side ofthe assignment operator receiving a copy of the value on the right-hand sideof the assignment operator. The value may be a primitive value or a referenceto an object. If the right-hand side of the assignment operator is anexpression, it is evaluated first.

Front 15

assignment operator

Back 15

An operator (=) used to assign a value to a variable in an assignmentstatement.

Front 16

assignment statement

Back 16

A statement that assigns a particular value to a variable

Front 17

attribute

Back 17

Some property or characteristic of an object that can be accessed using agetter method. Attributes are generally implemented by instance variables.Examples of such attributes are position and colour for Frog objects, andbalance and holder for Account objects.

Front 18

attribute value

Back 18

The current value of an attribute, often the same as an instance variable value,but possibly computed using instance variables.

Front 19

auto-boxing

Back 19

This is the automatic process of wrapping primitive values when called for bythe context of usage in a Java program.

Front 20

auto-unboxing

Back 20

This is the automatic process of unwrapping primitive values when called forby the context of usage in a Java program.

Front 21

automatic type conversion

Back 21

Where the Java compiler converts a value of some type to another typewithout the need for any explicit conversion of type on the part of theprogrammer. Automatic type conversion occurs in certain contexts, such as inan assignment statement when a compatible type on the right-hand side of theCombined glossary: Units 1–124assignment is converted to the type of the variable on the left-hand side of theassignment.

Front 22

behaviour

Back 22

A term used to describe the way in which an object behaves in response tothe messages in its protocol.

Front 23

binary digit

Back 23

Either of the two digits 0 and 1 in the binary number system. Binary digitsare used for the internal representation of numbers, characters and instructions.The binary digit is the smallest unit of storage.

Front 24

binary operator

Back 24

An operator that has two operands

Front 25

bit

Back 25

An abbreviation of binary digit

Front 26

body

Back 26

Another word for a statement block; for example, the body of a while loop isa statement block.

Front 27

Boolean condition

Back 27

A Boolean expression used to control the conditional execution of a statementblock.

Front 28

Boolean expression

Back 28

An expression that evaluates to either true or false.

Front 29

Boolean operator

Back 29

An operator used to combine simple Boolean expressions to form morecomplex Boolean expressions, which in turn can be combined with otherBoolean expressions. They are also known as logical operators.

Front 30

bucket

Back 30

A data structure that can contain zero or more unsorted elements. A HashSetuses buckets to implement a set. The hash code of each incoming element isused to decide which bucket to store it in.

Front 31

buffer

Back 31

Could refer to either an area used for temporary storage as data is transferredbetween a data source and a data sink, or a sequence of unfilled componentsthat allows a StringBuilder object to grow

Front 32

bug

Back 32

The cause of a run-time error

Front 33

bulk operations

Back 33

Operations that act on an entire collection without requiring the programmerto focus on individual elements.

Front 34

bytecode

Back 34

Bytecode is the intermediate code produced by the Java compiler. In BlueJ,compilation is done when the Compile button is pressed. This will create a bytecode file, for example, Frog.class, from the source code fileFrog.java. The bytecode file is portable because each computer that can runJava programs has a Java Virtual Machine that understands bytecode andconverts it into the machine code required for that particular computer.Bytecode is so-called because its instructions are a byte in size.

Front 35

call stack

Back 35

A representation of the order of methods called at some point during theexecution of a program, shown as a stack of method names, with the firstcalled method on the bottom and the last called method on the top.

Front 36

capacity

Back 36

The number of characters a StringBuilder object can hold.

Front 37

casting

Back 37

The prefixing of a value with the name of a type in parentheses in order toconvert a copy of that value into a different type. For example, (int) 99.0casts the value 99.0 into an int value

Front 38

catch

Back 38

The process of catching an exception, and the keyword introducing the clausein a try-catch statement that handles an exception.

Front 39

chaining

Back 39

Constructors are said to be chained, meaning that when an object is created,the constructors of all its superclasses are also called, either explicitly orimplicitly.

Front 40

checked exception

Back 40

An exception that the compiler requires the programmer to explicitly handleor declare may be thrown in a method header using a throws clause. Theseexceptions are ones that a programmer may reasonably be expected to catch orshould be made aware of.

Front 41

class

Back 41

A class is like a blueprint for the creation of objects and ensures that all itsinstances have the same instance variables and behave in response tomessages in an identical manner.

Front 42

class header

Back 42

The line in a class definition which gives its access modifier, name and,optionally, the name of a class it extends and the name(s) of any interface(s) itimplements. Example usage:public class WeatherFrog extends Frog implementsWeatherClient

Front 43

class method

Back 43

A class method is a method declared with the keyword static and isassociated with a class rather than with any of its instances. Classes are notobjects so code in a class method cannot use the expression this or thekeyword super. Class methods are invoked directly on the name of the class,using static binding, and so do not exhibit polymorphism.

Front 44

class variable

Back 44

A class variable is a variable declared with the keyword static. A classvariable is associated with a class rather than with any of its instances,although each instance of a class can access its own class’s class variables. Aclass only ever has one copy of each of its class variables. See qualified fordetails of how class variables are accessed.

Front 45

client (class)

Back 45

In programming, an object that uses a service provided by some other (server)class.

Front 46

collaboration

Back 46

The achievement of a software solution using two or more communicatingobjects.

Front 47

collection

Back 47

A collection consists of a number of, possibly zero, objects (strictly objectreferences) or primitives. The objects or primitives within a collection arereferred to as elements.

Front 48

Collection Classes/collection classes

Back 48

A set of library classes used to create various kinds of collection such as treestructures and queues. When capitalised, this phrase usually refers to classesthat are part of Java’s Collections Framework, which excludes array types.When used in lower case, the same phrase generally means any class thatimplements a collection (in the looser English language sense), which includesarray types.

Front 49

Collections Framework

Back 49

The Collections Framework includes a set of collection interfaces(Collection, Set, List, Map, and others), a set of collection classes(e.g. HashSet and HashMap) that implement them, and some supportingutility classes (e.g. Collections). The framework also includes a set ofassociated recommendations about constructors and about expected behavioursin common. Arrays are not part of the Collections Framework.

Front 50

comma-delimited file

Back 50

A file whose items of data (tokens) are separated by commas

Front 51

comment

Back 51

A comment is a piece of text in program code to assist human readers inunderstanding the code, and which the compiler ignores. In Java multi-linecomments are delimited by /* and */. End-of-line comments begin with twoforward slashes (//) and continue to the end of the line on which they begin.Javadoc comments are placed between the symbols /** and */ and mustappear immediately before a method, constructor or class header.

Front 52

common message protocol

Back 52

A set of messages shared by a number of classes. Often used to describe theset of messages specified by an abstract class for its concrete subclasses

Front 53

Comparable

Back 53

An interface that allows an element type to be sorted. It contains a singlemethod: compareTo().

Front 54

compareTo()

Back 54

The sole method of the Comparable interface. Allows classes of objectsimplementing this interface to be sorted (i.e. gives them a natural ordering).

Front 55

comparison operators

Back 55

A set of operators used for comparing values of expressions, including ==, >and < .

Front 56

compilation error

Back 56

An error detected by a compiler when code is compiled (which is known ascompile-time). No bytecode is generated if there are compilation errors.

Front 57

compiler

Back 57

Software which checks that text written in a high-level language is correctlyformed and, as far as can be determined before compilation, that it ismeaningful source code for the language

Front 58

component (of an array)

Back 58

The memory location at which an element (or a reference to it) of an array isstored.

Front 59

component type

Back 59

The type of the components of an array object; this determines the types ofthe object or primitive value that can be stored in the array.

Front 60

compound expression

Back 60

An expression built up using other sub-expressions, for example, thefollowing is a compound expression: (3 + 2) * (6 - 3).

Front 61

concatenation

Back 61

The joining of two strings. In Java the string concatenation operator is + (theplus sign). For example, "Milton " + "Keynes" evaluates to "MiltonKeynes".

Front 62

concrete class

Back 62

A class which is not abstract; a class for which instances can be created.

Front 63

conditional selection

Back 63

The use of if statements to select and execute alternative statement blocksbased upon the value of a Boolean condition.

Front 64

constant

Back 64

A constant is a variable whose value is fixed and unchangeable. Normally thekeyword final is used to make a value into a constant. In addition, whereonly a single value is needed for a class, constants are typically declared asstatic. However, static is not always used for constants, as sometimes a situation needs to be modelled where each instance of a class has its owndifferent constant value, such as a serial number.

Front 65

constant instance variable

Back 65

Constants are usually declared as final static variables. However,sometimes it makes more sense to define a constant as a final instancevariable. See constant for more information.

Front 66

constructor

Back 66

A programming construct, similar to a method, used to initialise a newlycreated object.

Front 67

constructor chaining

Back 67

The process whereby constructors use super() to invoke constructors higherup their inheritance hierarchy

Front 68

convention

Back 68

A commonly followed rule for implementing some feature of a softwaresystem that is not enforced by the language used, compiler, or platform onwhich the software is used

Front 69

data field

Back 69

A term encompassing instance variables and class variables as well asconstants

Front 70

data hiding

Back 70

The use of access modifiers to restrict access to class members, particularlyinstance variables, so that an object becomes a ‘black box’, with access to theencapsulated data (the instance variables) being possible only through alimited set of public methods.

Front 71

debugging

Back 71

The identification and removal of errors (bugs) from a program.

Front 72

declaration

Back 72

A statement in which memory is reserved for a variable of some type that isformed by writing the type of the variable followed by some name (itsidentifier).

Front 73

default constructor

Back 73

A zero-argument constructor that simply invokes super(). This constructor isprovided automatically by the compiler when the programmer has notspecified any constructor in a class.

Front 74

default values

Back 74

The values used by default to initialise instance variables of a class, whichmay be overwritten by another, explicit, initialisation.

Front 75

defensive programming

Back 75

A programming technique in which a method provides alternative paths todeal with expected and unexpected arguments. The method may return aBoolean to indicate success or failure, or (when necessary) use an exceptionto signal a failure

Front 76

delimiter

Back 76

A character used to mark where some part of a program starts or ends. Forexample, in Java, the character ; marks the end of a statement and thecharacter { marks the beginning of a statement block.

Front 77

design by contract (DbC)

Back 77

A programming technique in which a specification states a precondition forthe correct use of a method, and a postcondition that the method will achievein the event that its precondition is met. An exception is thrown by a methodwhen its precondition is not met.

Front 78

design principle

Back 78

In contrast to a guideline or suggestion, the word principle is reserved forrecommendations that apply universally or nearly universally. In this module,the term design principle is applied to principles governing how code shouldbe organised. The authors reserve the right sometimes to violate designprinciples for teaching reasons!

Front 79

destructive operation

Back 79

An operation on a collection that changes the contents of the collection insome way is said to be destructive. You may need to examine the Java API todetermine whether a method is destructive or non-destructive

Front 80

dialogue box

Back 80

A type of window with buttons through which users can be given informationby a program or provide information to a program on request. In M250,dialogue boxes are provided by class methods of the OUDialog class

Front 81

diamond operator

Back 81

From Java 7 onwards the diamond operator, written <> , simplifies theconstruction of collection objects. The compiler uses type inference todetermine the appropriate type of the collection based on the type of thecollection’s reference variable.

Front 82

difference

Back 82

For sets, the difference of A and B is all the elements in A that are not in B.This result is usually different from the difference of B and A. The term isused to refer both to the result and to the operation

Front 83

direct access (of an instance variable)

Back 83

Accessing an instance variable using its name, rather than using a gettermethod.

Front 84

direct interaction

Back 84

Direct interaction is not a formal technical term, but a descriptive phrase usedto describe a situation where one object has a reference to another, and thisreference is used to affect the state or behaviour of the other object. Contrastwith indirect interaction.

Front 85

direct subclass

Back 85

A class is a direct subclass of another class if it is directly below that class inthe class hierarchy

Front 86

dynamic binding

Back 86

The postponing of what method to select for execution in response to amessage until run-time. The method selected depends on the class of objectthat receives the corresponding message, rather than on the type of thevariable that references it

Front 87

dynamic compilation

Back 87

A compilation technique (used by the Java environment) generating realmachine code from bytecode (intermediate code). A chunk of bytecode iscompiled into machine code just prior to being executed. (This is differentfrom, and faster than, the piecemeal operation of an interpreter.) The realmachine code is retained so that subsequent execution of that chunk ofbytecode does not require the translation to be repeated.

Front 88

effective length

Back 88

The number of meaningful elements that a fixed-size collection actually holds.

Front 89

element

Back 89

The name given to the primitive value stored in, or the object referenced by,an array component

Front 90

encapsulation

Back 90

Encapsulation is the parcelling up of information and behaviour into areusable component. Objects allow you to encapsulate data by incorporatinginto a single entity (the object) both the data (instance variables) and thebehaviour (methods) defined for that data.

Front 91

entry

Back 91

An entry in a map means a key–value pair; that is, it refers to the combinationof a key and its associated value.

Front 92

equals()

Back 92

A method that determines whether two objects are equal or not. Since it isimplemented by the class Object, all classes of object understand themessage equals(), but the method is overridden to define versions ofequality appropriate to particular classes. For many classes, such as String,the method equals() is defined effectively to mean ‘has the same state as’.More generally, equals() is coded to mean ‘should be regarded as equal forour purposes’.

Front 93

escape character

Back 93

A character used to mark the start of an escape sequence in a string. In Javathis is the \ (backslash) character.

Front 94

escape sequence

Back 94

A sequence of characters beginning with a special escape character, such as abackslash, that allows subsequent characters to take on a different meaning forthe compiler.

Front 95

evaluate

Back 95

To find the value of something. We say that expressions have a value orevaluate to some value

Front 96

exception

Back 96

An object that is thrown by a method or the JVM as the result of a run-timeerror. The exception object holds details of what went wrong, allowing theexception handler that catches the exception to take appropriate action, orprovide a useful error message to the programmer.

Front 97

exception handler

Back 97

A block of code written to deal with (handle) an error that has been signalledwithin some program code. In Java, the error must have arisen in the contextof a try block, and the exception handler is in an associated catch block.The try and catch together make up a single statement.

Front 98

exception handling

Back 98

The programmed catching of an exception and the subsequent execution ofcode to abandon or continue execution, or to restore the software to ameaningful state.

Front 99

expression

Back 99

Code that evaluates to a single value. Expressions can be formed from literals,variables, operators and messages

Front 100

failing fast

Back 100

The programming philosophy which recommends that errors be signalled assoon as possible so that their cause can be more easily traced, and so thaterrors are not allowed to be passed on to other parts of a software system,potentially causing problems later. In Java this is done by throwing anexception.

Front 101

File

Back 101

An instance of this class contains the pathname to a file or folder in a systemindependentformat. The file specified need not exist; instead the pathnamemay point to a potential new file or folder.

Front 102

final

Back 102

The keyword final prevents a variable from ever having its value reassignedonce it has an initial value.

Front 103

finally

Back 103

Java keyword that introduces a block of code in a try-catch statement that willalways be executed, regardless of whether an exception occurs or not

Front 104

fixed-size collection

Back 104

A collection whose number of elements is fixed on creation. Such a collectioncan neither grow nor shrink.

Front 105

floating-point type

Back 105

A type capable of representing a decimal number (to a restricted level ofaccuracy).

Front 106

flushing

Back 106

The process of emptying a buffer so that no data remains in it, the data beingtransferred to a sink.

Front 107

for statement

Back 107

A statement allowing a statement block to be repeatedly executed according tothe value of a loop control variable (typically of type int) and a Booleancondition whose value is dependent on the loop control variable. for loopsare typically used when a fixed number of iterations is required. See alsowhile loop.

Front 108

for-each statement

Back 108

A statement that enables iteration through every element of a collection

Front 109

formal argument

Back 109

A typed identifier used in a method signature between parentheses to stand fora value (an actual argument) that is passed into the method body by amessage.

Front 110

formatting guidelines

Back 110

A set of guidelines which specify how program code should be laid out.

Front 111

garbage collection

Back 111

The process of destroying objects that have become unreachable because theyare no longer referenced by variables, in order to reclaim their space inmemory. In certain programming languages, including Java, this process isautomatic.

Front 112

generics

Back 112

A programming language feature that allows the writing of code that supportsmany types, but allows a particular type to be specified, so allowing for moretype checking to take place. Java collections from Java 5 onwards supportgenerics. When creating such a collection an element type is specified

Front 113

getter message

Back 113

A message that returns as its message answer the value of one of thereceiver’s attributes.

Front 114

getter method

Back 114

A method whose purpose is to return the value of one of an object’s attributesas its message answer. For example, the method getPosition() is a gettermethod that returns the value of the instance variable position held byinstances of the Frog class.

Front 115

graphical representation

Back 115

A visible representation of a software object that, by definition, is invisible.

Front 116

hash code

Back 116

In Java, a hash code is an int that can be calculated for any object, bysending it the message hashCode(). This method is inherited from Object,but in general must be overridden if equals() has been overridden. Hashcodes are used by sets and related collections to allow them to store elementsefficiently and to check rapidly for duplicates. If a class redefines equals(),then the hashCode() method for that class must take the definition intoaccount; otherwise the type will not behave properly in collections

Front 117

helper method

Back 117

A method whose purpose is to do some internal work of an object and whichtherefore should have private access so that it cannot be used by objects ofother classes

Front 118

hiding

Back 118

The situation in which a superclass member is not directly accessible in asubclass due to the subclass defining a member with the same name (for avariable) or same signature (for a method).

Front 119

high-level language

Back 119

A language (for example, Java) whose structure reflects the requirements ofthe problem, rather than the facilities actually provided by the hardware. Itenables a software solution to a problem, or a simulation of an aspect ofreality, to be expressed in a hardware-independent manner

Front 120

homogeneous collection

Back 120

A collection in which all the elements are of the same type. All collections inJava are homogeneous

Front 121

identifier

Back 121

The name given to a variable, method or formal argument.

Front 122

identity

Back 122

Identity refers to an object rather than its state. Two reference variables havethe same identity if they both reference the same object; that is, if they bothcontain a copy of the same reference value

Front 123

if statement

Back 123

A programming construct whereby one or more statement blocks areconditionally executed, according to whether a Boolean condition evaluates totrue or false.

Front 124

immutable

Back 124

An object whose state cannot be changed. An object whose state can bechanged is said to be mutable.

Front 125

implement

Back 125

In software development, to write the program code for some task orspecification. We also say that a class implements an interface when itimplements the interface and is able to understand all the messages specifiedby the method signatures of the interface

Front 126

implementation class

Back 126

A class that implements an interface, also known as an implementing class.For example, in the context of collections, ArrayList is an implementationclass for the List interface, it is an implementing class of List.

Front 127

implements

Back 127

A keyword in Java used in a class header to specify that the class implementsa particular interface. Example usage:public class SomeClass implements SomeInterface

Front 128

index

Back 128

An integer that is used to access the elements of an indexable collection.

Front 129

indexable collection

Back 129

A collection in which every element is accessed by an index

Front 130

indirect interaction

Back 130

Indirect interaction is not a formal technical term, but a descriptive phraseused to describe a situation where one object affects the state or behaviour ofthe other object, but without actually having a reference to that object –i.e. some intermediary object is used. Contrast with direct interaction.

Front 131

indirect subclass

Back 131

A class is an indirect subclass of another class if it inherits from that class viaone or more intermediate classes

Front 132

indirect superclass

Back 132

A class is an indirect superclass of another class, if it is above that class in theclass hierarchy but not directly above it.

Front 133

inheritance

Back 133

A relationship between classes by which they are organised into a hierarchy.According to the Java Language Specification (JLS), classes lower in ahierarchy are said to inherit all the accessible members from classes higher inthe hierarchy, other than those they override or hide. However, in generalobject-oriented terms, an object of class T is said to inherit all the members ofthe superclasses of T.

Front 134

InputStream

Back 134

The base class of a hierarchy of classes including FileInputStream,BufferedInputStream and ObjectInputStream, which are used to read(8-bit) byte streams. InputStream classes are used to read binary data

Front 135

inspector

Back 135

An inspector is a tool used in M250 to look at the value held (or objectreferenced) by a variable declared in the OUWorkspace. In the case of avariable referencing an object an inspector will show the internal state of thatobject, listing its attributes and their current values.

Front 136

instance

Back 136

An object that belongs to a given class is described as an instance of thatclass.

Front 137

instance method

Back 137

Code that is executed as the result of a message being sent to an object.

Front 138

instance variable

Back 138

A variable whose identifier and type is common to all the instances of a class,but whose value is specific to each instance. Each instance variable eithercontains a reference to an object or contains a value of some primitive type.For example, Frog objects have the instance variables colour andposition. The values of the instance variables of a particular objectrepresent the state of that object

Front 139

integrated development environment (IDE)

Back 139

A software tool that supports the development, compilation and execution ofcomputer programs. BlueJ is an example of an IDE that supports thedevelopment of programs in Java.

Front 140

interface

Back 140

(Java specific) An interface specifies a list of messages that a group ofunrelated classes, which are said to implement the interface, must be able toreceive. An interface lists only method headers (no method code), cannotdeclare any instance variables and cannot be instantiated. Classesimplementing an interface must be able to receive all the messagescorresponding to methods specified by that interface, either by defining therequired methods or inheriting them.

Front 141

interpreter

Back 141

A program that translates statements (rather than translating a whole program)from a high-level language, such as Java, to a machine code language, andexecutes the machine code.

Front 142

intersection

Back 142

Intersection is a mathematical operation on two or more sets that results in aset containing only the elements common to both sets. The term is used torefer both to the result and to the operation.

Front 143

invocation

Back 143

Executing code in a method. Class (static) methods are invoked directly ona class, whereas instance methods are invoked by sending messages toobjects. Also called method invocation

Front 144

iteration

Back 144

Also referred to as repetition. The repeated execution of a statement block foras long as some Boolean condition evaluates to true. Examples ofprogramming constructs in Java that support iteration are while and forloops.

Front 145

Java edition

Back 145

A category of Java targeted at a particular platform or domain, such asdesktop systems or mobile devices.

Front 146

Java Language Specification (JLS)

Back 146

The document that specifies the terminology used by the Java language anddescribes the manner in which various parts of the language work.

Front 147

Java Runtime Environment (JRE)

Back 147

The Java Runtime Environment (JRE) consists of the virtual machine (JVM)plus additional software, such as class libraries, that are needed to support therunning of Java programs on different platforms

Front 148

Java version

Back 148

A release of an edition of Java.

Front 149

java.util.Arrays

Back 149

A Java utility class that contains static methods for manipulating arrays

Front 150

Javadoc

Back 150

A programming tool that comes with Java. The Javadoc tool picks upinformation from specially formatted comments and other parts of the classcode such as the constructor and the method headers. These are all used tocreate an HTML file, which describes the class in a standard way. Thisdescription is aimed not at the Java compiler, but at human readers

Front 151

key

Back 151

A key is a value that can be used to uniquely identify any object from a givenmap-based collection. What constitutes a good key may depend on thepurpose of the collection.

Front 152

key set

Back 152

The set of all the key values for all the entries in some map. A key set istypically used to iterate over a map-based collection.

Front 153

key–value pair

Back 153

Maps can be viewed as a set of key–value pairs. Each entry in a map is akey–value pair. For example, a key might be a person’s name, and itsassociated value their telephone number

Front 154

keyword

Back 154

A Java keyword is a word reserved for use in the language. Keywords cannotbe used as variable identifiers

Front 155

lazy evaluation

Back 155

A type of evaluation used in compound Boolean expressions involving the &&and || operators whereby the second operand is evaluated only when it is necessary to do so in order to determine the truth value of the wholeexpression.

Front 156

length

Back 156

The number of elements an array can hold.

Front 157

list

Back 157

An ordered collection of variable size that permits duplicate elements

Front 158

literal

Back 158

A textual representation of a primitive value or object. For example, 'X' is achar literal, 4.237 is a double literal and "hello there!" is a Stringliteral.

Front 159

local variables

Back 159

A variable that is declared inside a statement block, such as inside a methodbody, or for statement, or, in the case of M250, the OUWorkspace. Thescope of such a variable is restricted to the statement block in which it isdeclared.

Front 160

logical error

Back 160

An error in logic, such as iterating for an incorrect number of times, orindexing an array at an incorrect position. Such an error may, or may not, leadto a program crash. Such errors may be detected while writing source code orduring the running of a program, or not at all

Front 161

logical operator

Back 161

An operator whose operands are Boolean values and which evaluates to aBoolean value; for example, the operator &&.

Front 162

loop

Back 162

In programming, a loop is a sequence of statements that is continuallyrepeated until some Boolean condition is reached.

Front 163

loop control variable

Back 163

A variable used to regulate the number of times a loop such as a forstatement or while statement is executed; such a variable is typically declaredinside a for loop’s header or before a while loop.

Front 164

low-level language

Back 164

A language written for direct programming of a computer's hardware. Eachtype of computer hardware needs its own low-level language.

Front 165

maintainability

Back 165

This is the extent to which a program can easily be maintained over a periodof time during which the requirements for the software may change.

Front 166

map

Back 166

A collection type that relates a set of keys to their corresponding values.

Front 167

mapping

Back 167

Another name for a key–value pair

Front 168

member

Back 168

The term member is a convenient word sometimes used to cover all of thefour following categories: class variables, class methods, instance variables and instance methods. Constructors are not members. Members are involvedin inheritance.

Front 169

message

Back 169

A message is a request for an object to do something. The only way to makean object do something is to send it a message. For example, the position of aFrog object changes when it is sent the message left() or right(); toobtain information on the value of a Frog object’s colour attribute, you sendit the message getColour().

Front 170

message answer

Back 170

When a message is sent to an object, then, depending on what the message is,a message answer may be returned. A message answer is a value or an object;it is not a message. Sometimes a message answer is used, sometimes it isignored. A message answer may be used subsequently as the receiver orargument of another message. Getter messages return the value of an attribute,as with the message getColour(), which returns a value such asOUColour.GREEN.

Front 171

message expression

Back 171

A message-send that evaluates to some value, i.e. the message returns amessage answer. We also say that it returns a value.

Front 172

message name

Back 172

The name of a message, including the following parentheses, but excludingany arguments. For example, the name of the message left() is left(),and the name of the message upBy(6) is upBy().

Front 173

message-send

Back 173

The code that sends a message to an object – for example, frog1.right(),which consists of the receiver followed by a full stop and then the message.

Front 174

method

Back 174

The code that is invoked by the Java Virtual Machine at run-time when anobject receives a message.

Front 175

method body

Back 175

That part of a method enclosed by braces that follows the method header. Thebody of a method is an example of a statement block.

Front 176

method header

Back 176

A method header consists of an access modifier (e.g. public), a return value(e.g. int or void) and a name (e.g. setPosition) followed by anyformal argument names enclosed in parentheses (e.g. (int aNumber)). Forexample, the method header for the method of the class Frog whose name issetPosition() is public void setPosition(int aNumber).

Front 177

method invocation

Back 177

At run-time, selecting and executing a method when an object receives amessage.

Front 178

method signature

Back 178

The name of the method together with the parentheses and the types of anyarguments. For example, the signature for the setPosition() method in theFrog class is setPosition(int).

Front 179

microworld

Back 179

A computer-based simulation with opportunities for manipulation of contentand practice of skills

Front 180

modal (dialogue box)

Back 180

A dialogue box that will not allow you to interact with another part of theprogram until you have responded to it by clicking one of the buttonspresented. All the dialogue boxes provided by the class OUDialog are modaldialogue boxes.

Front 181

model (verb)

Back 181

To simulate an entity in the problem domain using software

Front 182

mutator message

Back 182

Another name for a setter message

Front 183

mutator method

Back 183

Another name for a setter method

Front 184

natural ordering

Back 184

In Java, an element type is said to have a natural ordering if it implements theinterface Comparable and consequently has a compareTo()method. Fornumbers and strings, the natural ordering corresponds simply to everydaynumerical order and alphabetical order.

Front 185

new

Back 185

A keyword used to create an object – used in conjunction with a constructor

Front 186

non-destructive operation

Back 186

An operation on a collection that does not change the contents in any way

Front 187

object

Back 187

An instance of a class. An object has both state, represented by its attributes,and behaviour, its responses to the set of messages it understands (itsprotocol). An object models a part of a solution to a software problem.

Front 188

Object

Back 188

The top-level class in Java. Every class in Java other than Object is either adirect or an indirect subclass of Object.

Front 189

object diagram

Back 189

An object diagram represents an object. It shows the class of the object, itsstate in terms of attribute values, and its protocol.

Front 190

object initialisation

Back 190

The state of an object when it is first created depends on its initialisation, aprocess whereby its instance variables are set to known values. Thisinitialisation is usually carried out by the constructor in the object’s class

Front 191

object technology

Back 191

A synonym for object-oriented technology

Front 192

object-oriented programming

Back 192

An approach to programming in which a software problem is modelled usingclasses of objects that can achieve a solution by sending messages to oneanother

Front 193

object-oriented technology

Back 193

The technology associated with viewing software as being made up of objects

Front 194

operand

Back 194

An expression provided to an operator. A binary operator such as + has a lefthandoperand and a right-hand operand

Front 195

operating system (OS)

Back 195

The software that manages the resources of a computer, including controllingthe input and output, allocating system resources, managing storage space,maintaining security and detecting equipment failure.

Front 196

operator

Back 196

A symbol used as a function, that is, it has one or more values it operates onand returns a value

Front 197

orchestrating instance

Back 197

An orchestrating instance is a separate object used to tie together the differentparts of a complicated interaction that do not seem to belong to any single oneof the objects involved

Front 198

ordered collection

Back 198

A collection where each element in the collection has a well-defined place, asindicated by its index number. Thus, an ordered collection allows us to accessand find the first, second or last element etc. However, the order does nothave to reflect anything to do with the elements themselves. It is simplydetermined by where each element has been placed in the list. This contrastswith a sorted collection

Front 199

OutputStream

Back 199

The base class of a hierarchy of classes including FileOutputStream,BufferedOutputStream and ObjectOutputStream, which are used towrite (8-bit) byte streams. OutputStream classes are used to write binarydata.

Front 200

overloading

Back 200

A method is said to be overloaded when there are other methods, defined inthe same class, or inherited (in the JLS sense) from some superclass, with thesame name but a different method signature, i.e. different types and/ornumbers of arguments.

Front 201

@Override

Back 201

A Java annotation used to indicate that a method is intended to override aninherited method

Front 202

overriding

Back 202

The process of redefining (replacing) a method that would have been inherited(JLS definition) from a superclass so as to cause it to have different behaviour.A method that overrides a method from a superclass has the same signatureand return type as the superclass method.

Front 203

parameter

Back 203

A synonym for argument

Front 204

pathname

Back 204

A textual representation of how to find a file or folder on a particularoperating system

Front 205

peripheral device

Back 205

Any part of the computer that is not part of the essential computer (i.e. theCPU and main memory), such as a mouse, keyboard or flash drive.

Front 206

persistence

Back 206

The ability of objects or other data to continue in existence after a programhas stopped executing.

Front 207

persistent

Back 207

Stored in a non-volatile form, that is, a form that is not lost when thecomputer's power is turned off. The most common form of persistent storageis a file on a disk drive.

Front 208

polymorphic method

Back 208

A method with the same signature as some other method, but which typicallydefines different behaviour. For example the method home() defines differentbehaviour for Frog, Toad and HoverFrog objects. In Java, polymorphismoccurs when classes in inheritance hierarchies override methods as well aswhen several classes implement some interface

Front 209

postcondition

Back 209

A condition that is true after some code (particularly a method) is executed

Front 210

postfix operator

Back 210

An operator that appears after its operand(s).

Front 211

precedence rules

Back 211

Rules for determining the order in which various operators are evaluated in acomplex expression

Front 212

precondition

Back 212

A condition that must be true before some code is executed in order for thatcode to behave correctly. The user of a method typically checks itsprecondition before using it

Front 213

primary sort

Back 213

An initial sorting according to a particular key

Front 214

primitive data type

Back 214

A set of values together with operations that can be performed on them. Theprimitive data types in Java provide a set of basic building blocks from whichall of the more complex types of data can be built. Java’s primitive data typesinclude int, char and boolean.

Front 215

primitive type variable

Back 215

A variable declared to hold a value of the declared or compatible primitivedata type. Less formally we refer to a primitive variable

Front 216

primitive value

Back 216

A value of some primitive type; for example, true, -1.3, 42, or 'x' are allprimitive values of different primitive types

Front 217

private

Back 217

An access modifier that restricts access to a class member to objects of theclass to which it belongs

Front 218

private protocol

Back 218

The part of the protocol of a class or object that is inaccessible from a contextoutside of the class itself

Front 219

problem domain

Back 219

The collection of real-world entities within the application area that exhibit thebehaviours that the required system has to model.

Front 220

procedural programming

Back 220

An approach to programming in which a problem is broken down intosmaller, simpler procedures, often incorporating global data structures

Front 221

program

Back 221

A software solution to a problem, typically on a small scale (compared tolarger application software).

Front 222

protected

Back 222

Java access modifier used to restrict access of a member of a class X tosubclasses of X and classes within the same package as class X.

Front 223

protocol

Back 223

The set of messages an object understands

Front 224

public

Back 224

An access modifier applied to a class member that allows all classes of objectsto have access

Front 225

public protocol

Back 225

The part of the protocol of a class or object that is accessible from outside ofthe class itself.

Front 226

qualified

Back 226

The qualified name of a member is its simple name prefixed by the name ofits enclosing class, as in OUDialog.request. The parts of such names areseparated by dots. This means that different classes can have members withthe same names – the qualified names allow them to be distinguished fromone another

Front 227

raw collection

Back 227

A collection for which an element type is not specified. Java collections priorto Java 5 are raw collections and contain only references of class Object

Front 228

Reader

Back 228

The base class of a group of classes including FileReader andBufferedReader, which are used to read 16-bit character streams. Readerclasses are used to read text files

Front 229

receiver

Back 229

The object to which a message is sent.

Front 230

recursive method

Back 230

A method that calls itself as part of its method definition. This can lead toindefinite looping when an attempt is made to execute the method. However,used properly, it can be an extremely powerful approach.

Front 231

refactoring

Back 231

Refactoring is when code is rewritten without changing its overall effect, butfor the purpose of improving its design, removing code duplication, orimproving maintainability.

Front 232

reference type variable

Back 232

A variable declared to hold a reference to an object of the declared type (or acompatible type). Less formally we refer to a reference variable

Front 233

relative pathname

Back 233

A path to a file beginning from the current working directory, often resultingin a shorter path than an absolute path.

Front 234

return type

Back 234

The type of value returned by a method.

Front 235

run-time

Back 235

The period during which a program is executing, in contrast to the time periodduring which it is loaded or compiled.

Front 236

run-time error

Back 236

A programming error that becomes apparent only when the program is run,and has not been detected beforehand. Run-time errors can be caused bylogical errors, failure to account for different ways in which code might beused, or conditions outside of the control of the programmer.

Front 237

Scanner

Back 237

A class used to read string tokens from a source. In M250 the source may bea FileReader or a String.

Front 238

scope

Back 238

The scope of a variable describes the areas of program code from which thevariable may be used. The scope of a local variable is from the point where itis declared to the end of its enclosing statement block.

Front 239

secondary sort

Back 239

A sorting that can be applied after applying a primary sort in order to sort anyelements that are considered equal by the primary sort

Front 240

selection

Back 240

A technique by which a statement or statement block is executed subject tosome Boolean condition. An if statement is used to perform selection inJava.

Front 241

self-documenting code

Back 241

Code written using well-chosen names and structures so as to make itsintentions relatively clear when read

Front 242

sequence diagram

Back 242

A diagram that depicts the interactions required between objects to carry out aparticular task; this collaboration is shown in the form of messages andmessage answers.

Front 243

set

Back 243

A collection in which each item may appear only once – no duplicates areallowed.

Front 244

setter message

Back 244

A message that sets the value of one of a receiver’s attributes. See also gettermessage

Front 245

setter method

Back 245

A method whose purpose is to assign a new value to an instance variable. Forexample, the method setPosition() is a setter method for the instancevariable position held by instances of the Frog class.

Front 246

software

Back 246

A general term for all programs that can be run on a desktop computer oranother hardware platform, such as a mobile phone

Front 247

software component

Back 247

A piece of software that can be readily combined with other components toconstruct more complex software.

Front 248

sorted collection

Back 248

A collection that always keeps its elements in their natural ordering, if any.This contrasts with an ordered collection, where the ordering may just be anaccident of where elements happen to have been placed in the collection

Front 249

source code

Back 249

Program text expressed in a high-level programming language.

Front 250

stable sort

Back 250

A sort that does not reorder equal elements

Front 251

stack trace

Back 251

A stack of textual information ordered from the last thing that happened downto the first thing that happened that is displayed when an exception is thrownand not handled; a representation of a call stack.

Front 252

state

Back 252

The values of the attributes of an object constitute its state. The state of anobject can vary over time as the values of its attributes change.

Front 253

statement

Back 253

A statement represents a single instruction for the compiler to translate intobytecode. In Java most statements end with a semicolon.

Front 254

statement block

Back 254

A statement or sequence of statements ‘bundled together’ for use in aparticular context. Any sequence of statements can be turned into a block byenclosing it in braces (curly brackets).

Front 255

static

Back 255

A Java keyword that defines a variable or method as belonging to a classrather than its instances

Front 256

static binding

Back 256

The selection by the compiler at compile time (rather than a virtual machine atrun-time) of a method to be executed at run-time. In the case of classmethods, the compiler chooses the method from the class whose name is usedto qualify the method name, or based on the type of the reference variable. Incomparison, instance methods can be selected for execution at run-time basedon the type of the receiver object.

Front 257

stream

Back 257

An object used to connect a data source to a data sink, enabling data to betransferred from the source to the sink.

Front 258

string

Back 258

A sequence of characters enclosed in quotation marks; an object of typeString

Front 259

string interning

Back 259

A process used by Java to create a pool of strings that can be reused whenpossible, which may result in the sharing of string literals.

Front 260

StringBuilder

Back 260

A class whose instances represent a mutable sequence of characters

Front 261

strong typing

Back 261

A programming language feature that requires variables to have a declaredtype and enforces rules on the ways in which those types can be used,including what types of values can be assigned to variables of those types andwhat operators values of those types can be used with. Languages (such asJava) that feature strong typing are said to be strongly typed

Front 262

sub-array

Back 262

A set of contiguous components within the same array.

Front 263

subclass

Back 263

A subclass is any class which extends (inherits from) another class. In Java allclasses except Object are subclasses of some other class

Front 264

subclassing

Back 264

Defining a class as a subclass of an existing class

Front 265

subinterface

Back 265

A subinterface is an interface that extends another interface (called itssuperinterface), thereby inheriting the signatures of the parent interface, andwhich typically contains additional method signatures

Front 266

sublist

Back 266

A list together with any two positions in the list may be seen as defining anew list containing just those elements between the two positions, retainingthe same order. The new list is known as a sublist.

Front 267

substitutability

Back 267

The principle in object-oriented programming whereby, wherever the systemexpects an object of type X, an object of class Y can always be substitutedinstead, where class Y is a subclass of X, or where class Y implements aninterface of type X.

Front 268

substitution

Back 268

The technique of providing an instance of one class in a situation where aninstance of a different class is expected. In Java, an object can be assigned toa variable whose type has been declared as some superclass of the object, orwhich has been declared as an interface type which that object’s classimplements. Similarly, an object can be used as an actual argument to amethod where the formal argument’s type has been declared as somesuperclass of the object, or which has been declared as an interface typewhich that object’s class implements

Front 269

subtype

Back 269

A type whose values (in the case of primitive types) or instances (in the caseof class types) are substitutable for another type’s values. For example, asubclass type is a subtype of a superclass type. A class that implements aninterface is a subtype of the interface type

Front 270

super

Back 270

A Java keyword that allows the writing of expressions to access members of aclass that are inaccessible using the expression this, due to hiding oroverriding; for example, super.x or super.x() causes the JVM to start itssearch for the corresponding member in the superclass of the receiver. Themember must be accessible for such code to compile

Front 271

super()

Back 271

Used within a constructor to invoke the constructor without any arguments inthe direct superclass. May also be used with n arguments to invoke asuperclass constructor with n formal arguments

Front 272

superclass

Back 272

If B is a subclass of A, then A is the superclass of B. In the Java programminglanguage a subclass has only one direct superclass

Front 273

superinterface

Back 273

A superinterface is an interface that is extended by some other interface(s).

Front 274

supertype

Back 274

A type that supports substitution of more specific types. Both interface typesand superclass types (including abstract class types) are examples ofsupertypes. See also subtype.

Front 275

syntax

Back 275

The syntax of a programming language is the set of rules governing thestructure of the language, including its valid symbols, expressions andstructures. Syntax rules define the form of the various constructs in thelanguage, but say nothing about the meaning of these constructs

Front 276

syntax error

Back 276

An error that occurs as a result of failure to observe a syntax rule. Such anerror is detected during compilation by a compiler

Front 277

testing

Back 277

The process of using test cases to check that code is behaving as theprogrammer intended, and to help discover bugs

Front 278

this

Back 278

An expression used within a method or constructor to reference the objectexecuting the method or constructor

Front 279

this()

Back 279

Used within a constructor to invoke the constructor without any arguments inthe current class. May also be used with n arguments to invoke a constructorwith n formal arguments in the current class.

Front 280

throw

Back 280

The process of throwing an exception, also referred to as raising or signallingan exception

Front 281

throws clause

Back 281

A part of a method header beginning with the keyword throws, followed bya comma-separated list of any exceptions the programmer wants to declare tobe thrown. If a checked exception is not handled, it must be declared in athrows clause.

Front 282

token

Back 282

An item of data that can be written to or retrieved from a file. Delimiters areused to separate tokens in a file.

Front 283

tree

Back 283

A collection structure typified by branching connections between elements,often used to create collections of items sorted according to some criteria

Front 284

try-catch statement

Back 284

An exception handling statement, a mechanism to catch exceptions. If apossible checked exception is not declared in a throws clause, it must behandled using a try-catch statement

Front 285

unary operator

Back 285

An operator that has just one operand; for example, the minus operator

Front 286

unchecked exception

Back 286

An exception for which the compiler does not require any explicit exceptionhandling code and that the compiler does not require the programmer todeclare as thrown in a method header. These are errors that may not be easilyrecovered from, or should not be recovered from; instead, program logic orother issues may need to be resolved

Front 287

union

Back 287

Union is a mathematical operation on two or more sets that results in a setcontaining all of the elements of all of the sets. The term is used to refer bothto the result and to the operation.

Front 288

unwrapping

Back 288

The process of converting a wrapped value (one contained in a wrapper class)to its primitive value equivalent

Front 289

utility class

Back 289

A utility class is one that provides methods (usually static) that performcommon functions. The Math class is an example.

Front 290

variable

Back 290

A named ‘chunk’ or block of the computer’s memory which can hold either avalue of some primitive type or a reference to an object

Front 291

variable initialisation

Back 291

The process of assigning a variable a value for the first time

Front 292

variable reference diagram

Back 292

A diagram showing the relationships between reference variables, objects andtheir instance variables. Object protocol is not included

Front 293

virtual machine (VM)

Back 293

A layer of software that simulates a computer capable of interpretingbytecode

Front 294

visibility

Back 294

Visibility of an item (such as a member or constructor) in a class refers towhether or not parts of a class can access that item directly. Same asaccessibility

Front 295

void

Back 295

A keyword used in Java to indicate that a method does not return a value

Front 296

while statement

Back 296

A loop that allows a statement block to be repeatedly executed depending onthe value of some Boolean condition. while loops are typically used to repeatcode when the number of iterations cannot be determined in advance. See alsofor loop

Front 297

workspace variable

Back 297

Workspace variables (such as in the OUWorkspace) behave like localvariables, except that their lifetime lasts until you close or reset theworkspace, rather than ending when a particular block has finished executing

Front 298

wrapper class

Back 298

Every primitive type has a corresponding wrapper class whose purpose is tohold a primitive value in a place where a primitive value is intuitively what isneeded, but where the type checking requires an object. For example, thewrapper class of int is Integer. Wrapper classes are used in auto-boxing

Front 299

wrapping

Back 299

The process of converting a primitive value to an object equivalent, using awrapper class

Front 300

Writer

Back 300

The base class of a group of classes including FileWriter andBufferedWriter, which are used to write 16-bit character streams. Writerclasses are used to write text files

Front 301

zero-based indexing

Back 301

An indexing system in which the first index is 0.