IB computer science

Constructor

In OOP a special type of method which has the same name as the class and is used to create objects. This creation process is known as instantiation.

Instantiate

The creation of an instance or particular realisation of an abstraction or template such as a class. The product of this is an object of the class type. In OOP this is done by using a particular method called a constructor.

Object/Instance

When a class is instantiated the product is one of these. In OOP it is normally what is returned from the constructor.

Class

An extensible program-code-template for creating objects, providing initial values for state (member variables) and implementations of behavior (member functions or methods).

Method/Subroutine

A procedure associated with an object class. These procedures should be logical in terms of scope and function and written to encourage re-use.

Variable

A storage location paired with an associated symbolic name (an identifier), which contains some known or unknown data referred to as a value. In many computer languages the data type is defined and fixed.

Static

A Java keyword. It can be applied to a variable, a method or an inner class. The variables, methods or classes defined by this keyword have a single instance for the whole class and all it's associated objects. It can be accessed when no Object has been instantiated.

Final

A Java keyword. It can be applied to a variable, a method or class and indicates that it cannot be changed , derived from over ridden or extended.

Public

An access modifier. A class, method, constructor or interface that is declared like this can be accessed from any other class.

All methods, and variables declared like this are inherited by subclasses.

Private

An access modifier. Variables, methods and constructors that are declared like this can only be accessed from within the class.

It is the most restrictive access level. Classes cannot be declared like this.

It is the main way that an object encapsulates itself and hides data from outside the class.

Protected

An access modifier. Variables, methods and constructors that are declared like this can only be accessed by subclasses in other packages or from other classes within the same package.

Cast

A reference to one object or data type can be changed to a reference to another object or data type by this process. The objects in the class need to be related by inheritance or in the case of primitives have a defined way of changing available.

Inheritance

In this coding construct a class that is derived from another class is called a subclass (also a derived class, extended class, or child class). The class from which the subclass is derived is called a superclass (also a base class or a parent class).

Subclasses gain access to the public and protected members and methods of the superclass directly but not the private members and methods. Hence the Objects of the subclass become hybrids of the super and sub classes.

Polymorphism

In simple terms it is the ability to define a method of the same name that operates differently depending on the class in which it is defined not the data type of the object from which it is referenced.

Encapsulation

This is used to refer to one of two related but distinct notions, and sometimes to the combination thereof:

A language mechanism for restricting access to some of the object's components.

A language construct that facilitates the bundling of data with the methods (or other functions) operating on that data.

Extensibility

Something, such as a program, programming language, or protocol, that is designed so that users or developers can expand or add to its capabilities

Getter/Accessor

A method that returns a member variable and helps to maintain it's encapsulation.

Setter/Mutator

A method that can be used to limit or restrict the changes allowed for a member variable. This can maintain a limited amount of encapsulation.

Exception

An event, which occurs during the execution of a program, that disrupts the normal flow of the program's instructions. When an error occurs within a method, the method creates an object and hands it off to the runtime system.

Primitive

Datatypes that are not derived from the Object class and are directly contained values. Java has 8 of these:

byte

short

int

long

char

float

double

boolean

Data Type

In Java, every variable has a type declared in the source code. There are two kinds of types: reference types and primitive types. Reference types are references to objects.

Object Oriented Programming

It provides a clear modular structure for programs which makes it good for defining classes and their associated objects. These classes can be implemented so as to keep details of the algorithms and data hidden through a clearly defined interface. This encourages encapsulation.

The classes may inherit from one another to promote reusability of code and methods can be over ridden in class hierarchies giving rise to the benefits of polymorphism.

Procedural Program

Code that has a traditional start to finish flow and does not support classes, inheritance, polymorphism or encapsulation.

Algorithm

A process or set of rules to be followed in calculations or other problem-solving operations, especially by a computer.

Initialization

A special kind of assignment: the first, before, objects have null value and primitive types have default values such as 0 or false. Can be done in conjunction with declaration.

Association

A relationship between two objects which may be either a dependency (uses) or aggregation (is made up of).

UML

A way of defining the interface, methods, member variables of a class and how they relate to other classes in the system in a graphical form.

Aggregation

A relationship between two objects which indicates that one is made up of the other. For example a car has a relationship with it's wheels.

Decomposition

The breaking down of a complex problem into smaller parts that are easier to understand. In the case of OOP systems are broken down into smaller classes or objects.

Abstraction

The process of identifying the properties and behaviours of real things or ideas that need to be represented in code.

Dependancy

A relationship between two objects where one requires, but does not instantiate another

Arguments/Parameters

Objects or primitives passed into a method for use by it's internal algorithms.

Return

The output of a Function and a keyword in Java.

Procedure

A type of method that performs a task and does not return a value

Function

A type of method that may performs a task but will always return a value

Overloading

Methods within a class that have the same name and return the same data type but take different arguments.

Over riding

Methods within an inheritance hierarchy that have the same signature ( return, name and arguments) but different implementations depending on the class they are defined in. This is the basis of polymorphism.

Maintainability

The ease with which changes and fixes can be made to a program.

Libraries

Collections of related code that can be imported into a program to allow the developer to perform standard actions in a re-usable and easy way.

Instance Variable

A variable defined in a class (i.e. a member variable), for which each instantiated object of the class has a separate copy, similar to a class variable. Static variable are not included in this definition.

Local Variable

Variables that are only visible within the block of code within which they are declared. These blocks may be method wide, or within a loop or if for example. The area of it's visibility is known as it's scope.

Signature

The method declaration. It is the combination of the method name, return type and the parameter list.

Extends

A keyword used to indicate that one class inherits from another.

Algorithm

A series of steps designed to solve a mathematical or other problem

Pseudocode

A method of describing an algorithm using structured English close to programming langauge

Flow chart

A diagrammatic method of showing the structure and data flow to define a problem and its solution

Flowchart Symbol: Rectangle

A process to be completed

Flowchart Symbol: Rhombus

A decision

Flowchart Symbol: Oval

Start or End to an algorithm

Machine code

Instructions in binary used by the CPU

Assembly Language

A low-level programming language that uses more memorable mnemonic codes and labels to represent machine-level code. Each instruction corresponds to just one machine operation

Assembler

A program to convert assembly-level commands into machine code

Low-level Language

a programming language that requires little or no translation to produce machine code.

High-level language

A programming language that resembles natural language. Each instruction translates to many machine instructions. It is problem based rather than machine based

Fundamental Operation

A task that can be performed natively by a CPU

Compound Operation

A task that requires a combination of many fundamental operations for a CPU to complete

Source Code

The program written by the end user in a high-level language before it is converted to machine code

Compiler

Translation software that converts high level source code into machine code by analysing whole blocks of source code

Interpreter

Translation software that converts source code into machine code by analysing only one source code instruction at a time.

Selection

Using a condition to decide on what instructions to execute next

Iteration (loop)

A group of instructions is executed repeatedly until a condition is met

Integer

Whole number, positive or negative, with no decimal or fractional part

Boolean

A value that can only be true or false

Character

A single letter, number, or symbol

String

A series of letters, numbers, and/or symbols

Primitive Variable

A label referring to a location in memory containing a value that can be accessed or changed by a program

Constant

A label referring to a location in memory containing a value that can be accessed but not changed by a program

Declaration

Identifying a variable or constant or array to a program so that memory space can be aollocated

Assignment

Setting the value of a variable

Operator

A logical, arithmetic or comparison symbol

Comparison

Comparing the values of two items and returning TRUE of FALSE depending on the results

Syntax error

The rules of a language are broken by the program

Logic error

The program produces results that are different to what the programmer expected

run-time error

The program encountered a value, condition, or state that was not executable.

Validating data

Data used in testing that represents normal data that could be expected

Bubble Sort

A simple algorithm that repeatedly steps through the list to be sorted, compares each pair of adjacent items and swaps them if they are in the wrong order. The pass through the list is repeated until no swaps are needed, which indicates that the list is sorted

Selection Sort

Repeatedly finds the next largest (or smallest) element in the array and moves it to its final position in the sorted array.

Binary Search

Start examining values of an array in the center and narrow down your search, halving the search area each time.

Linear Search

Examine the values of each element in an array one by one

Method

A re-usable unit of code. When called, execution returns to the source of the call when the unit is complete

Procedure

A method that does not return a value

Function

A method that returns a value

Parameter

a value passed to a method

Array

A data structure containing a fixed-size list of values/objects of the same type

Index

an integer that refers to the position of data in an Array