Java final keyword

Java final keyword

Java final keyword: In this tutorial, we will find out about Java final variables, methods, and classes with examples.

In Java, the final catchphrase is used to denote constants. It very well may be used with variables, methods, and classes.

When any element (variable, method, or class) is proclaimed final, it very well may be doled out just a single time. That is,

• the final variable cannot be reinitialized with another value
• the final method cannot be overridden
• the final class cannot be extended

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1. Java final Variable

In Java, we cannot change the value of a final variable. For example,

class Main {
  public static void main(String[] args) {

    // create a final variable
    final int AGE = 32;

    // try to change the final variable
    AGE = 45;
    System.out.println("Age: " + AGE);
  }
}

In the above program, we have made a final variable named age. Also, we have attempted to change the value of the final variable.

At the point when we run the program, we will get a compilation error with the accompanying message.

cannot assign a value to final variable AGE
    AGE = 45;
    ^

Note: It is recommended to use uppercase to declare final variables in Java.

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2. Java final Method

Before you learn about final methods and final classes, make sure you know about the Java Inheritance.

In Java, the final method cannot be overridden by the child class. For example,

class FinalDemo {
    // create a final method
    public final void display() {
      System.out.println("This is a final method.");
    }
}

class Main extends FinalDemo {
  // try to override final method
  public final void display() {
    System.out.println("The final method is overridden.");
  }

  public static void main(String[] args) {
    Main obj = new Main();
    obj.display();
  }
}

In the above example, we have made a final method named show() inside the FinalDemo class. Here, the Main class acquires the FinalDemo class.

We have attempted to override the final method in the Main class. At the point when we run the program, we will get a compilation mistake with the accompanying message.

 display() in Main cannot override display() in FinalDemo
  public final void display() {
                    ^
  overridden method is final

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3. Java final Class

In Java, the final class cannot be inherited by another class. For example,

// create a final class
final class FinalClass {
  public void display() {
    System.out.println("This is a final method.");
  }
}

// try to extend the final class
class Main extends FinalClass {
  public  void display() {
    System.out.println("The final method is overridden.");
  }

  public static void main(String[] args) {
    Main obj = new Main();
    obj.display();
  }
}

In the above example, we have created a final class named FinalClass. Here, we have tried to inherit the final class by the Main class.

At the point when we run the program, we will get a compilation error with the accompanying message.

cannot inherit from final FinalClass
class Main extends FinalClass {
                   ^

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Java OOP (I)