Computer Science - Option D: Key terms and definitions

Class

an extensible program-code-template for creating initial values for states (variables) and implementations of behaviours (functions/procedures/methods)

Identifier

a named pointer that explicitly identifies an object, class, method, or variable

Primitive

the most basic data type available within the Java language

The 8 primitive data types:

boolean, byte, char, short, int, long, float, double

Variable

a value that a program can manipulate in a named storage location, but must be declared before they can be used

Instance variables

• Non-static variable

• Declared in a class outside any method, constructor or block

• Use access modifiers (private, public, protected)

• Example: int engMarks, int mathsMarks

Parameter variables

• the passing of information/instructions into functions or procedures

• Example: (int x, int y)

Arguments

the values that are passed into parameters

Local variable

• a variable defined within a block, method, or constructor

• Example: int age = 0;

Method

a set of code that can be called at any point in a program by utilising the name

Accessor

returns the value of a private instance (class) variable, also known as a getter method

Mutator

control changes to an encapsulated instance (class) variable/state, also known as a setter method

Constructor method

an instance method that is invoked when an object of that class is created

Object creation rule in Java

When an object is created, one of the constructor method in the class must be invoked (to initialise the instance variables in the object)

The difference between method and constructor

Method	Constructor
Method can be any user-defined name	Constructor must be class name
Should have return type	It shouldn’t have any return type (even void)
Method should be called explicitly either with object reference or class reference	Be called automatically whenever object is created
Method is not provided by compiler in any case	Java Compiler provides a default constructor if there isn’t one

Method signature

Combination of the method name and the parameter list

Return value

Used to exit from a method, with or without a value.

Method procedures

don’t return any value (void)

Method functions

return a value

The 3 Java access modifiers

public, protected, private

Public

can be accessed from any other class

Private

• can only be accessed within the declared class itself

• classes can’t be private but methods and variables can

• if public getter methods are present in the class, private variables can be accessed outside the class

Protected

accessed only by the subclasses

Summary of access

Modifier	Class	Package	Subclass	World
Public	Y	Y	Y	Y
Protected	Y	Y	Y	N
No modifier	Y	Y	N	N
Private	Y	N	N	N

extends

used in a sub class to inherit the properties of a super class

Static

• a non-access modifier that is applicable for the following: blocks, variables, methods, nested classes

• precede its declaration with the keyword static

Encapsulation

hiding methods or variables so other classes cannot manipulate them without going through

The 4 OOP Fundamentals

Abstraction, Polymorphism, Inheritance, Encapsulation

Inheritance

the mechanism by which one class is allowed to inherit the features (states and behaviors) of another class

includes Super Class and Sub Class

Advantages of inheritance

• minimises the amount of duplicate code in an application by sharing common code amongst several subclasses

• better organisation of code

• code is more flexible to change

Super Class

The class whose features are inherited is known as a super class (or base class or parent class) 

Sub Class

The class that inherits the other class is known as subclass. The subclass can add is own states and behaviors in addition to the superclass states and behavior

Types of loops

While, do-while, count-controlled

Static arrays

do not change

Features of modern programming languages that enable internationalisation

• Common character sets (e.g. Unicode, ASCII)

• Platform independent high level languages let code run on many platforms5

Open source movement

supports the use of open-source licences….