Understanding significance of final in Java

Final modifier in Java spans its influence on

Key Take Aways

Type :

• A final class is one which can be not be inherited any further.
• A final class is a class which has all its method defined , there are no abstract methods in the class.
• A final class signifies the end of the inheritance chain .
• A final class is the opposite of abstract class.

Field

• Final modifier when applied to a field signifies the field cannot change its value once initialized.
• The initialization can be done via a initializer or constructor at time of object instantiation.
• Final modifier when applied to the field signifies that the value cannot be changed.
• If the final field is of primitive type the value of the variable cannot be changed.
• if the field field is of Class Type , then the reference is bound to the object for the lifetime.The Object can change its state though

Methods:

• Final modifier when applied to method means it cannot be overriden in any of the subclass.

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Code:

package com.big.data.java.modifiers;

import java.util.HashMap;
import java.util.Map;

final class ParentClass {
    int a;
};

// public class ChildClass extends ParentClass not possible as parentClass is final



public class FinalDemo {

    // value set as part of initialization
    final int a = 10;

    // value needs to be set in constructor
    final Map<String, String> mapReference;

    public FinalDemo() {

        //a = 20; not possible as 10 has been set in the intialization
        mapReference = new HashMap<>();
    }

    public void changeMap() {

        // mapReference = new HashMap<>(); not possible as mapReference is final and has been  initialized in constructor.


        // Object new HashMap<>() can change its state but reference needs to keep pointig at mapReference = new HashMap<>();
        mapReference.put("1", "1");


        //a = 20; primitive type cannot change its value as it is final
    }

}