Overriding

[renuka_renukut]

Hi !

I have questions on overriding and abstraction, encapsulation , If any one can tell me that


Q.1 How to prevent overriding?
Q.2 Example on abstraction !
Q.3 Example on encapsulation !


Thanks

[r035198x]

When you read the books and tutorials, what did they say were the answers to those questions?

[j2me64]

Hi !

I have questions on overriding and abstraction, encapsulation , If any one can tell me that


Q.1 How to prevent overriding?
Q.2 Example on abstraction !
Q.3 Example on encapsulation !


Thanks

Ok for Q.1: You can prevent overriding by declaring your method final. So when the class is extended by a subclass the subclass can't override the final method.

How much do you offer for Q.2 and Q.3 :)

[j2me64]

Q.2 Example on abstraction !

Here is an example of an abstract class with only two methods, one abstract and the other concrete.

// if one method in a class is abstract, then
// the whole class must be declared abstract.
// but the abstract class can have concrete methods.

public abstract class AbstractClass {
	public void method1() {
		System.out.println("concrete method1 from AbstractClass");
	}
	
	public abstract void method2();

}

here is the example that uses the AbstractClass

// abstract classes can't be instantiated, but only 
// extended, that's why the keyword extends
// is used. in order to work, all abstract methods 
// must be emplomented before they run correctly.

public class AbstractExample extends AbstractClass {
	
	// here method2 is implemented
	// the concrete method1 from AbstractClass is inherited
	
	public void method2() {
		System.out.println("implemented method2 from AbstractExample");
	}
	public static void main(String[] args) {
		AbstractExample example = new AbstractExample();
		example.method1();
		example.method2();
	}
}

Q.3 Example on encapsulation !

first, what is encapsulation? according to What Is an Object? (The Java™ Tutorials > Learning the Java Language > Object-Oriented Programming Concepts)

Hiding internal state and requiring all interaction to be performed through an object's methods is known as data encapsulation

simplifying, in java encapsulation is done by declaring your member variables as private, so that the can't be accessed directly from outside the class but only through public setters and getters. a small example is

public class Bycicle {
	private int speed = 0;
	private int gear = 1;

	public int getSpeed() {
		return speed;
	}

	public void setSpeed(int speed) {
		this.speed = speed;
	}

	public int getGear() {
		return gear;
	}

	public void setGear(int gear) {
		this.gear = gear;
	}
}

for details about abstraction see also Abstract Methods and Classes (The Java™ Tutorials > Learning the Java Language > Interfaces and Inheritance)