Java · Theory

Inheritance in Java

Theory

33/270

Inheritance in Java

Inheritance lets a child reuse and extend a parent. Keyword: class Dog extends Animal. IS-A idea: Dog is an Animal, so Dog can use parent features.

Java allows one parent class only (single class inheritance). Write common code once in the parent. Special code goes in the child. The child can add new methods and override parent methods.

Deep inheritance trees become hard to change. Keep them shallow. Extra capabilities come from interfaces: one superclass + many interfaces.

Let's take this on the board with one tiny Main class — no extra files. Inheritance in Java — output: Eating then Bark. Dog did not rewrite eat — it inherited it from Animal. Start from main, go line by line, and stop at each print. That output is the proof for Inheritance.

Diagram

Animal
      sound()
        │ extends
        ▼
       Dog
      sound()  →  bark

Exam tip

IS-A + single class inheritance + interfaces for extra contracts.

Example

class Animal {
  void eat() { System.out.println("Eating"); }
}
class Dog extends Animal {
  void bark() { System.out.println("Bark"); }
}
public class Main {
  public static void main(String[] args) {
    Dog d = new Dog();
    d.eat();
    d.bark();
  }
}

Inheritance in Java — output: Eating then Bark. Dog did not rewrite eat — it inherited it from Animal.

Short notes

DefInheritance = child reuses and extends parent. Dog extends Animal.
RuleIS-A. Java allows one parent class only.
RememberCommon code in parent. Special code in child. Child can override.
UseOne superclass + many interfaces for extra contracts.

Java · Theory

Inheritance in Java

← All stacks

Theory

33/270

Inheritance in Java

Inheritance lets a child reuse and extend a parent. Keyword: class Dog extends Animal. IS-A idea: Dog is an Animal, so Dog can use parent features.

Java allows one parent class only (single class inheritance). Write common code once in the parent. Special code goes in the child. The child can add new methods and override parent methods.

Deep inheritance trees become hard to change. Keep them shallow. Extra capabilities come from interfaces: one superclass + many interfaces.

Diagram

Animal
      sound()
        │ extends
        ▼
       Dog
      sound()  →  bark

Exam tip

IS-A + single class inheritance + interfaces for extra contracts.

Example

class Animal {
  void eat() { System.out.println("Eating"); }
}
class Dog extends Animal {
  void bark() { System.out.println("Bark"); }
}
public class Main {
  public static void main(String[] args) {
    Dog d = new Dog();
    d.eat();
    d.bark();
  }
}

Inheritance in Java — output: Eating then Bark. Dog did not rewrite eat — it inherited it from Animal.

Short notes

DefInheritance = child reuses and extends parent. Dog extends Animal.
RuleIS-A. Java allows one parent class only.
RememberCommon code in parent. Special code in child. Child can override.
UseOne superclass + many interfaces for extra contracts.

Inheritance in Java

Example

Short notes

Questions

Inheritance in Java

Example

Short notes

Questions