• Local scope if it is only accessible from the structure within which it is declared.
• Global scope if it is accessible from all parts of the program.

1. Only three program structures are used: sequence, selection and iteration
2. Designed from the top down
3. Modular

Problem decomposition: a large task is broken down into smaller subtasks until each subtask accomplishes one identifiable task.

1. Large programs can be split in modules that are easier to read, debug and maintain.
2. Several modules can be worked on at the same time.
3. Modules can be reused in other programs.
4. Each module can be individually tested.

1. Detailed program structures are not shown.
2. Selection and iteration not specified.

A blueprint for an object: specifying the attributes and methods which capture common characteristics and behaviours.

An abstract data type and one instance of a class.

Creating an object based on a class, using a constructor method.

The current values of one instance of a class' attributes.

All of an objects methods, procedures and data are wrapped into a single entity.

It uses the concept of information hiding, so that many developers may interact with an object as an abstract data type written by others without knowing how its methods are implemented.

Subclasses may share all the attributes and methods of the superclass, and then extend it with new attributes and methods.

1. Polymorphism describes the ability to process objects differently based on their class.
2. Overriding describes defining a method within a subclass with the same identifier as method in the superclass, but changing its implementation.
3. Polymorphism is achieved through overriding.

• Inheritance: x "is a" type of y
• Association: x "has a" y

Aggregation, Composition.

If the container object is destroyed, the constituent objects still exist independently.

If the container object is destroyed, then the constituent objects are also destroyed.

1. Favour composition over inheritance.
2. Encapsulate what varies.
3. Program to interfaces not implementation.

1. Constituent objects may not need all the methods and attributes of its parent object.
2. Composition results in a more flexible relationship.

Reduce maintenance and testing difficulty.

Methods and procedures should be called based on how a third party would like to interact with the abstract data type, not how the abstract data type would carry out its objectives.

Aggregation - weaker association - white diamond on the container object.

Composition - stronger association - black diamond on the container object.

1. Public.
2. Private.
3. Protected.

Can be accessed by methods within the defining class, via inheritance and via reference to object of a class (identifier for an instance).

Can only be accessed by methods within the defining class.

Can be accessed by methods within the defining class, via inheritance and only if it is in a subclass definition.

• public = +
• private = -
• protected = #

1. Rigidly enforced modular structure: makes it easier to maintain.
2. Simpler to extend and adapt programs using composition and inheritance.
3. Code can be reused in other programs without the other knowing how it works: encapsulation and modular structure.