3 keywords to avoid override method

Java provide 3 keyword to avoid override method at sub-class are :

• private
• static
• final

 Private keyword

private keyword is putted in frond of method  to hide the access from out class even sub-class. so sub-class cannot override it but can create a new method the same charactor as super class.

class A {
	 
	void show(){
		System.out.println("Show Class A");
	}
	private void display(){
		System.out.println("Class A");
	}
}

class B extends A{
	// it work properly 
	@Override
	void show(){
		System.out.println("Show Class B");
	}
//	 Error because method display() in class A is private(hidden)
//	cannot find any method to override 
//	but it will  not error if delete annotation @Override
	@Override
	public void display(){
		System.out.println("Class B");
	}
}

class Main{
	public static void main(String [] args){
		B b = new B();
		b.show();
		b.display();
	}
}

Method display if class A hide (private keyword)  so cannot be override.

static keyword

Following are some important points for method overriding and static methods in Java.
1) For class (or static) methods, the method according to the type of reference is called, not according to the abject being referred, which means method call is decided at compile time.

2) For instance (or non-static) methods, the method is called according to the type of object being referred, not according to the type of reference, which means method calls is decided at run time.

3) An instance method cannot override a static method, and a static method cannot hide an instance method.

class A {
	 
	void show(){
		System.out.println("Show Class A");
	}
	private void display(){
		System.out.println("Class A");
	}
	
	public static void testStatic(){
		System.out.println("test Static in Class A");
	}
}

class B extends A{
	// it work properly 
	@Override
	void show(){
		System.out.println("Show Class B");
	}
//	 Error because method display() in class A is private(hidden)
//	cannot find any method to override 
//	but it will  not error if delete annotation @Override
//	@Override
	public void display(){
		System.out.println("Class B");
	}
	@Override
	public static void testStatic(){
		System.out.println("test Static in Class b");
	}
}

public class Main{
	public static void main(String [] args){
		B b = new B();
		b.show();
		b.display();
		B.testStatic();
	}
}

final keyword 

final keyword used to make class, data member, or method as Constance which cannot be change.

• final data member is a constance
• final member method cannot be overridden
• final call cannot extend

// error cannot extend (inheritance )
// remove keyword final to fix
 final class A {
	 
	 final int x = 10;
	 A(){
//		  error cannot modified
//		 remove keyword final or delete a line below to fix
		 this.x = 20;
	 }
 
	
	public final void testFinal(){
		System.out.println("test Static in Class A");
	}
}

class B extends A{
	// it work properly 
 
//	 error cannot override 
//	remove this method or remove keyword final in super-class testFinal() 
	@Override
	public  void testFinal(){
		System.out.println("test Static in Class b");
	}
}

public class Main{
	public static void main(String [] args){
		B b = new B();
		 
		B.testFinal();
	}
}