Home » Java Book » Class » Class Creation »

Understanding static

A static method can be used by itself. Here shows how to declare static method.


static void aStaticMethod(){
}

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;

  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:


x = 42
a = 3
b = 0

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

 
public class Main { 

    static int a = 3; 
    static int b; 

}

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;
  }
}

To call a static method from outside its class, use the following general form:


ClassName.method( )

Here is an example. The static method callme( ) and the static variable b are accessed outside of their class.

 
class StaticDemo {
  static int a = 4;
  static int b = 9;

  static void callme() {
    System.out.println("a = " + a);
  }
}
public class Main {
  public static void main(String args[]) {
    StaticDemo.callme();
    System.out.println("b = " + StaticDemo.b);
  }
}

Here is the output of this program:


a = 4
b = 9

« The Person class: another demo

finalize Method »

java2s.com | Contact Us | Privacy Policy

All other trademarks are property of their respective owners.