Inheritance and Composition

Inheritance

Inheritance enables you to reuse code that has already been defined by a class.

Inheritance in Java is a concept that acquires the *properties from one class to other classes.

*properties are variables in a class.

For example:

public class Employee {
	private String name;
	private int salary;
	
	public getName() {
		return this.name
	}
}

In the class above, name and salary are properties of an instance of the class (object of the class) while getName() is a method.

// class child(subclass) extends parent(superclass) {}
class Parent {}
class Child extends Parent {}

A subclass inherites all the members (*fields, methods, and nested classes) from its superclass.

*A field is a class, interface, or enum with an associated value.

class Point {
	int x;
	int y;
}

// case 1.
class Point3D {
	int x;
	int y;
	int z;
}

// case 2.
class Point3D extends Point {
	int z;
}

*Both case 1 and case 2 have 3 members in the address being pointed to by the reference variable.

*reference variable is one that refers to the address of another variable. (참조변수)

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