Java final keyword

Final Keyword is used to stop user accessing the java variable or class or method. We can use final keyword in following three manner -

1. Making Final Variable
2. Making Final Method
3. Making Final Class

Way 1 : Final Variable

If we make the variable final then the value of that variable cannot be changed once assigned. Consider the following example -

package com.c4learn.inheritance;
public class ShapeClass {
    final int SHAPE_SIDES = 3;
    void setShape() {
    	SHAPE_SIDES = 4;   	
    }
    public static void main(String[] args) {
    	ShapeClass c1 = new  ShapeClass();
    	c1.setShape();
    }
}

Output :

Compile Time Error

We cannot modify the value of the final variable, we will get following error message -

Way 2 : Final Method

We cannot Override the final method as we cannot change the method once they are declared final. Consider the following example -

package com.c4learn.inheritance;
public class ShapeClass {
    int SHAPE_SIDES = 3;
    final void setShape() {
    	SHAPE_SIDES = 4;   	
    }
    public static void main(String[] args) {
    	ShapeClass c1 = new  ShapeClass();
    	c1.setShape();
    }
}
class Circle extends ShapeClass {
    void setShape() {    // Error Here
    	SHAPE_SIDES = 4;   	
    }	
}

Output :

Compile Time Error

In this example we have declared method as final so we cannot override the final method, otherwise we will get compile time error -

Way 3 : Final Class

We cannot inherit the final class.

package com.c4learn.inheritance;
public final class ShapeClass {
    int SHAPE_SIDES = 3;
    final void setShape() {
    	SHAPE_SIDES = 4;   	
    }
    public static void main(String[] args) {
    	ShapeClass c1 = new  ShapeClass();
    	c1.setShape();
    }
}
class Circle extends ShapeClass { // Error Here
}

Output :

Compile Time Error

In this example we have declared class as final so we cannot inherit the final class

Some Important Points : Final Keyword

1. Final Keyword can be applied only on Method,Class and Variable

2. Final Variable must be initialized at the time of declaration or inside constructor
3. Re-Assigning Value is not allowed for final member variable
4. Local Final Variable should be initialized during the time of declaration
5. Final and Finally both are different. Finally keyword is used on Exception handling in Java