Inheritance in Java

Inheritance is a mechanism through which a class can inherit properties(fields and methods) of another class. This allows to resuse the fields and methods of the parent class.

Inheritance also represents the IS-A relationship which describes the parent-child relationships between the classes.

Types of Inheritance

Java allows 5 types of Inheritance:

types-of-inheritance-1 types-of-inheritance-2

Single - One class inherits another class.

class A {
  public void method() {
    // Do Something
  }
}

class B extends A {
  public void anotherMethod() {
    // Do Something
  }
}

Multilevel - A chain of inheritance.

class A {
  public void method() {
    // Do Something
  }
}

class B extends A {
  public void anotherMethod() {
    // Do Something
  }
}

class C extends B {
  public void yetAnotherMethod() {
    // Do Something
  }
}

Hierarchical - Two or more classes inherit a class.

class A {
  public void method() {
    // Do Something
  }
}

class B extends A {
  public void anotherMethod() {
    // Do Something
  }
}

class C extends A {
  public void yetAnotherMethod() {
    // Do Something
  }
}

Multiple - A class inherits multiple interfaces. Java does not allow inheriting multiple classes as if the two parent classes have same name properties then there will be a conflict.

interface A {
  public void interfaceMethod();
}

interface B {
  public void interfaceMethod();
  public void anotherInterfaceMethod();
}

class C implements A, B {
  public void interfaceMethod() {
    // Implementation of interfaceMethod
  }
  public void anotherInterfaceMethod() {
    // Implementation of anotherInterfaceMethod
  }
}

Hybrid - Mix of Multiple and Hierarchical inheritance.

interface A {
  public void interfaceMethod();
}

interface B extends A {
  public void anotherInterfaceMethod();
}
interface C extends A {
  public void yetAnotherInterfaceMethod();
}

class D implements B, C {
  public void interfaceMethod() {
    // Implementation of interfaceMethod
  }
  public void anotherInterfaceMethod() {
    // Implementation of anotherInterfaceMethod
  }

  public void yetAnotherInterfaceMethod() {
    // Implementation of yetAnotherInterfaceMethod
  }
}

Types of Inheritance#

Types of Inheritance