Java final keyword tutorial

The final keyword is used to restrict some related member variable, method or class.

• final variables

  Once you initialize the final variable, you cannot modify it. There are 3 possible types of final variable initializations.

  
  

  • final variable can initiazile in a assignment statement

  • final variable can initiazile in a constructor

  • static final variable can initiazile in a static block

  public class StaticClass {
      private final String VAR_1 = "VAR_1";         //initiazile in a assignment statement
      private final static String VAR_2 = "VAR_2";  //initiazile in a assignment statement
  
      private final String VAR_3;
  
      private final static String VAR_4;
  
      static {
          VAR_4 = "VAR_4";                    //initiazile in a static block
      }
  
      public StaticClass() {
          VAR_3 = "VAR_3";                    //initiazile in a constructor
      }
  }





• final class

  A final class cannot be subclassed. You cannot extend a final class into another.





• final methods

  A final method cannot be overridden in a subclass. That class will be a concrete class for parent class and children both.

      public class Bird {
          private String name;
          public Bird(String name) {
              this.name = name;
          }
          protected final void sing() {
              System.out.println("Bird " + name + " is singing");
          }
      }

  We will get a similar error like below during the compilation if we try to override the final method in a child class.

  HummingBird.java:17: error: sing() in HummingBird cannot override sing() in Bird
          protected void sing() {
                         ^
        overridden method is final
      1 error
      

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