Study College Course - Software Design Patterns - OOP and UML Class Diagrams OOP and Java (lec1)

Lecture 1：OOP and UML Class DiagramsOOP with Java

OOP and UML Class Diagrams OOP and Java

Object-Oriented Programming Object-Oriented Programming

Superclass and subclass
Superclasses and subclasses

Abstraction
– Modelling attributes and behaviors of real objects, in specific contexts
Abstraction - modeling the properties and behavior of real objects, specifically

At the top level
overhead
– public, or package-private (no explicit modifier)
Public or package private (no explicit modifier)
At the member level
At the membership level
– public, private, protected, or package-private (no explicit modifier)
public, private, protected or package-private (no explicit modifiers)

Classes can be derived from other classes, inheriting fields and methods
Classes can be derived from other classes, inheriting fields and methods
Definitions
define
– Subclass (derived class/extended class/child class)
– Superclass (base class/parent class)
- Subclasses (derived classes/extended classes/subclasses)
- Superclass (base class/parent class)
Every class has one and only one direct superclass (single inheritance)
Each class has one and only one direct superclass (single inheritance)
– Excepting Object, which has no superclass
It has no superclasses except Object
A subclass inherits all the members (fields, methods, and nested classes) from its superclass
Subclasses inherit all members of their superclasses (fields, methods, and nested classes)

Use the inherited members as is, replace them, hide them, or supplement them
Use inherited members as is, replace them, hide them, or supplement them

Declare a field in the subclass with the same name as the one in the superclass, thus hiding it (NOT recommended)
- Hide a field in a subclass by declaring it with the same name as the field in the superclass (not recommended)
Write a new instance method in the subclass that has the same signature as the one in the superclass, thus overriding it
- Override it by writing a new instance method in the subclass with the same signature as the field in the superclass
Write a new static method in the subclass that has the same signature as the one in the superclass, thus hiding it
-Write a new static method in a subclass that has the same signature as the static method in the superclass, thus hiding it
Write a subclass constructor that invokes the constructor of the superclass
- Write a subclass constructor that calls the superclass constructor

How about private members in a superclass?

An abstract class is a class declared abstract: it may or may not include abstract methods
An abstract class is a class declared to be abstract: it may or may not contain abstract methods
An abstract method is a method declared without an implementation
Abstract methods are methods that are declared but not implemented
Final methods and classes
Final Methods and Classes
Methods called from constructors should generally be declared final
- Methods called from a constructor should normally be declared final.

Interfaces are contracts
The interface is the contract.
A reference type, containing only constants, method signatures,default methods, static methods, and nested types
Reference types, containing only constants, method signatures, default methods, static methods, and nested types
Cannot be instantiated
Cannot be instantiated
– They can only be implemented by classes or extended by other interfaces
- They can only be implemented by classes or extended by other interfaces
Consisting of modifiers, keyword, interface name, a comma-separated list of parent interfaces (if any), and the interface body
Consists of modifiers, keywords, the interface name, a comma-separated list of parent interfaces (if any), and the interface body
Interface body can contain abstract methods, default methods,and static methods
Interface bodies can contain abstract methods, default methods, and static methods

Include an implements clause in the class declaration
Include the implements clause in the class declaration
– Your class can implement more than one interface
- Your class can implement multiple interfaces
If you define a reference variable whose type is an interface,any object you assign to it must be an instance of a class that implements the interface
If a reference variable of type interface is defined, any object assigned to it must be an instance of a class that implements the interface