Java Unit 1-5

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Access modifier

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A keyword that controls the visibility of class members to objects of other classes. The modifiers 'private' and 'public' are the most frequently used access modifiers.

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Accessor message

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Another name for a 'getter message'

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Accessor method

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Another name for a 'getter method'

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Actual argument

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An actual argument is a value used in a message that is copied to a formal argument for use inside the corresponding method. Actual arguments must be of a compatible responding formal arguments.

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Assignment

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

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Assignment operator

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

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Assignment statement

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A statement that assigns a particular value to a variable (see assignment)

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Attribute

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Some property or characteristic that can be accessed using a getter method. Attributes are generally implemented by instance variables. examples of such attributes are 'position' and c'olour' for 'frog' objects and 'balance' and 'holder' for 'account' objects

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Attribute value

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

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Automatic type conversion

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Where the java compiler converts a value of some type to another type without the need for any explicit conversion of type on the part of the programmer. Automatic type conversion occurs in certain contexts, such as in an assignment statement when a compatible type on the right-hand side of the assignment is converted to the type of the variable on the left-hand side of the assignment.

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Behaviour

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A term used to describe the way in which an object behaves in response to the message in it's protocol

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Binary digit

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

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Binary operator

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An operator that has two operands

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Bit

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An abbreviation of a binary digit.

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Statement Block

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A statement or sequence of statements 'bundle together' for use in a particular context. Any sequence of statements can be turned into a block by closing it in braces (curly brackets)

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Body

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

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Boolean condition

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A boolean expression used to control the conditional execution of a statement block.

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Boolean expression

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An expression that evaluates to either 'true' or 'false'.

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Boolean operator

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An operator used to combine a simple boolean expressions to form more complex boolean expressions, which in turn can be combined with other boolean expressions. They are also known as 'logical operators'.

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Bytecode

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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 file 'Frog. Java'. The bytecode file is portable because each computer that can run Java programs has a Java virtual machine that understands bytecode and converts it into the machine code required for that particular computer. Bytecode is so called because it's instructions are a byte in size

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Casting

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

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Class

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A class is like a blueprint for the creation of objects and ensures that all its instances have the same instance variables and behave in response to messages in an identical manner

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Class header

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The line of code in a class definition that provides information about the class such as it's name and access modifier. A class header must include the keyword 'class'. Example simple usage: 'public class marionette'

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Class method

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Classes, as well as defining instance methods, can also define class methods. These are methods that can be executed irrespective of whether any instances of a class of been created. A class method is executed as a result of an invocation (not by sending a message to an instance of a class). Class methods in Java are specified by including the 'static' keyword in a method header.

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Comment

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A comment is a piece of text in program code to assist human readers in understanding the code, and which the compiler ignores. In Java mult-iline comments are delimited by /* and */. End of line comments beginning with two for slashes (//) and continue to the end of the line of which they begin. Javadoc comments are placed between the symbols /** and */ and must appear immediately before a method, constructor or class header.

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Comparison operators

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

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Compiler

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A program that first checks that source code written in a high-level language is syntactically correct. If the check is successful the compiler translates the source code into bytecode or machine code. The java compiler translates source code into bytecode.

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Software component

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

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Compound expression

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

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Concatenation

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