Inheritance

Inheritance in Java
Inheritance is a compile-time mechanism in Java that allows you to extend a class (called the base
class or superclass) with another class (called the derived class or subclass).
In Java,inheritance is used for two purposes:
1. class inheritance - create a new class as an extension of another class, primarily for the purpose
of code reuse. That is, the derived class inherits the public methods and public data of the
base class. Java only allows a class to have one immediate base class, i.e., single class
inheritance.
2. interface inheritance - create a new class to implement the methods defined as part of an
interface for the purpose of subtyping. That is a class that implements an interface “conforms
to” (or is constrained by the type of) the interface. Java supports multiple interface inheritance.
In Java, these two kinds of inheritance are made distinct by using different language syntax. For
class inheritance, Java uses the keyword extends and for interface inheritance Java uses the
keyword implements.
public class derived-class-name extends base-class-name {
// derived class methods extend and possibly override
// those of the base class
}
public class class-name implements interface-name {
// class provides an implementation for
}

Example of class inhertiance
package MyPackage;
class Base {
private int x;
public int f() { ... }
protected int g() { ... }
}
class Derived extends Base {
private int y;
public int f() { /* new implementation for Base.f() */ }
public void h() { y = g(); ... }
}
In Java, the protected access qualifier means that the protected item (field or method) is visible to a
any derived class of the base class containing the protected item. It also means that the protected
item is visible to methods of other classes in the same package. This is different from C++.

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