Dezign Patterns

Inheritance

📦 Definition: One class (child/subclass) inherits the properties and behavior of another (parent/superclass).
🎯 Intent : Code reuse and logical hierarchy.


class Vehicle {
    void startEngine() {
        System.out.println("Engine started.");
    }
}

class Car extends Vehicle {
    void playMusic() {
        System.out.println("Playing music.");
    }
}

Java supports multiple inheritance


interface A {
    default void hello() {
        System.out.println("Hello from A");
    }
}

interface B {
    default void hello() {
        System.out.println("Hello from B");
    }
}

class MyClass implements A, B {
    // Must override hello() to resolve ambiguity
    public void hello() {
        A.super.hello();  // Or B.super.hello();
    }
}

Feature	Java 7	Java 8
Multiple class inheritance	❌	❌
Multiple interface inheritance	✅	✅
Multiple inheritance of behavior	❌	✅ (now with default methods!)
Multiple inheritance of state	❌	❌

Though they say the java supports multiple inheritance , but it doesn't support "Multiple inheritance of state"


class A {
    String test;
    public void display() {
        System.out.println(test);
    }
}

class B {
    String test;
    public void display() {
        System.out.println(test);
    }
}

// class can't extent multiple classes  -- compile time error
class C extends A , B {

    @Override
    public void display() {
        System.out.println(super.test);
    }
}