Java

Front 1

What is a fundamental way to handle complexity?

Back 1

Use abstractions: it denotes the essential properties and behaviors of an object to differentiate it from other objects. The hard part is to find the right abstraction.

Front 2

What is a class?

Back 2

It's a blueprint for creating objects (or abstractions of the real world)

Front 3

What is the process of creating objects from a class?

Back 3

Instantiation / an object is an instance of a class

Front 4

What is an object reference?

Back 4

A variable that can store a reference value to an instantiated object

Front 5

What's the only way to manipulate an object in java?

Back 5

Through its reference value

Front 6

Can you refer to an object with multiple references?

Back 6

Yes, they are called aliases (CharStack a=new CharStack; CharStack b=a;)

Front 7

What happens when there are no more references to an object?

Back 7

The automatic garbage collector can run, so the memory can be reclaimed and reallocated

Front 8

Does each created object get its own copies of fields?

Back 8

Yes. They are called instance variables and they comprise the object's state.

Front 9

What defines an object's state?

Back 9

The values of its instance variables (if two objects have the same values, they have the same state)

Front 10

What defines an object's behavior?

Back 10

Its methods

Front 11

How do objects communicate?

Back 11

By message passing (i.e., invoking each other's methods)

Front 12

What is the "dot" in a method call called?

Back 12

The "binary infix dot" operator, but the "dot" operator can also be used to reference fields of an object

Front 13

What is an "instance member"

Back 13

They are both instance variables and instance methods of an object. They can only be accessed or invoked through an object reference.

Front 14

What is an "instance variable"

Back 14

A field that is allocated when the class if instantiated (i.e., when an object of the class is created). It's also called a non-static field.

Front 15

What is an "instance method"?

Back 15

A method that belongs to an instance of the class. Objects of the same class share its implementation.

Front 16

What is a "static member"? How can they be accessed?

Back 16

These are both static variables and static methods of a class. They can be accessed or invoked either by using the class name or through an object reference.

Front 17

What is a "static variable"? When is it allocated?

Back 17

A field that is allocated when the class is loaded. It belongs to the class and not to any specific object of the class. It's also called a static field or a class variable?

Front 18

What is a "static method"?

Back 18

A method that belongs to the class, and not to any object of the class. It's also called a class method.

Front 19

What are the two funadamental mechanisms to build a new class from an existing one?

Back 19

(1) Inheritance and (2) aggregation (i.e., a composite object)

Front 20

When does it make sense to model a new class with inheritance?

Back 20

When the new class will inherit all the properties of the parent class. In other words, the child class is going to be a more SPECIALIZED version of the parent class.

Front 21

When does it make sense to model a new class with aggregation?

Back 21

When the new class is comprised of multiple different classes

Front 22

What are the key terms in inheritance?

Back 22

The child class is called the subclass, and the parent class is the superclass. The subclass EXTENDS the superclass.

Front 23

How does Java support aggregate objects?

Back 23

By reference. I.e., you have to create reference variables to the constituent objects

Front 24

What are the two different types of values in Java?

Back 24

There are (1) reference variables that hold references to instances of classes and there are (2) atomic values of primitive data types.

Front 25

Can objects in Java contain other objects?

Back 25

Only by holding references to other values (i.e., reference values)

Front 26

How many objects can you have in a .java file?

Back 26

As many as you want except that each public class must have its own .java file

Front 27

What is a lexical token?

Back 27

The low-level language elements that form the building blocks for more complex constructs. Identifiers, numbers, operators, and special characters are examples of tokens that can be used to contract high-level constructs like expressions, statements, methods, and classes.

Front 28

What is an identifier?

Back 28

A name in a program: identifiers can be used to denote classes, methods, variables, and labels. In Java, an identifier is composed of a sequence of characters, where each character can be either a letter or digit. The first character has to be a letter.

Front 29

Can you use a currency symbol or underscore as the first letter of an identifier in Java?

Back 29

Sure, but you should probably avoid it

Front 30

Can use an @ symbol in an identifier?

Back 30

No

Front 31

What is a keyword?

Back 31

It's a reserved word that's already predefined in the language and you can't use it to denote other entities.

Front 32

What is a literal?

Back 32

It denotes a constant value (i.e., a value that remains unchanged in the program). Examples are 2000, 0, -7, 3.14, 'a', true, "abba", and null

Front 33

What's the default data type of a literal?

Back 33

It's going to be an int unless you specify it as a different type (like a long by using L as a suffix)

Front 34

What's the default data type of a floating point?

Back 34

Double unless you tell it to be a float with "F"

Front 35

What are the three categories of primitive data types in java?

Back 35

Integrals: signed integers (byte, short, int, long) and unsigned character values; floating point types: float, double; and boolean types

Front 36

Is a primitive data type an object?

Back 36

No, but there are wrapper classes that you can use

Front 37

How wide is the float and the double?

Back 37

The float is 32 bits wide, the double is 64 bits wide

Front 38

What's the difference between default values in fields and methods?

Back 38

The values of fields are set automatically and you don't need to initialize them. They values for local fields of local methods are not, however. The compiler reports an error if you try to compile them without initialized values.

Front 39

Discuss the lifetime of a variable

Back 39

Its lifetime depends on the context in which it was declared. It's also referred to as its scope. I.e., if it's an instance of an object, or a static variable, or local to a method, construct, or block.

Front 40

What was the idea behind the JavaBeans standard?

Back 40

It would like reusable software components be modelled in Java. Especially with builder tools that could take advantage of the components.

Front 41

What are some of the key naming patterns in JavaBeans?

Back 41

The properties of the object should be private, and they should start with a lower case letter. You should wrap them with getter and setter methods.