Java Tutorial - Java static final

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Java static keyword

A static class member can be used independently of any object of that class.

A static member that can be used by itself, without reference to a specific instance.

Here shows how to declare static method and static variable.

static int intValue;

static void aStaticMethod(){
}

Restrictions

Methods declared as static have several restrictions:

• They can only call other static methods.
• They must only access static data.
• They cannot refer to this or super in any way.

All instances of the class share the same static variable. You can declare a static block to initialize your static variables. The static block gets only called once when the class is first loaded.

The following example shows a class that has a static method

 
public class Main {
  static int a = 3;
  static int b;
/*from ww  w. j  ava  2s .  c  om*/
  static void meth(int x) {
    System.out.println("x = " + x);
    System.out.println("a = " + a);
    System.out.println("b = " + b);

  }

  public static void main(String args[]) {
    Main.meth(42);
  }
}

The output:

Example

The following example shows a class that has the static variables.

 
public class Main { 
    static int a = 3; 
    static int b; 
}

We can reference the static variables defined above as follows:

Main.a

The following example shows a class that has a static initialization block.

public class Main {

  static int a = 3;

  static int b;

  static {
    System.out.println("Static block initialized.");
    b = a * 4;
  }
}

Java final keyword

A final variable cannot be modified. You must initialize a final variable when it is declared. A final variable is essentially a constant.

Final variables

 
public class Main {
  final int FILE_NEW = 1;
  final int FILE_OPEN = 2;
}

Prevent overriding

Methods declared as final cannot be overridden.

 
class Base {/*from w  w w  . ja  v a  2  s. c o m*/
  final void meth() {
    System.out.println("This is a final method.");
  }
}

class B extends A {
  void meth() { // ERROR! Can't override.

    System.out.println("Illegal!");

  }
}

If you try to compile the code above, the following error will be generated by the compiler.

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