Java Tutorial/Class Definition/static Member

Define the static member

1. You can use the keyword static in front of a field or method declaration.
2. The static keyword may come before or after the access modifier.

These two are correct:

   <source lang="java">

public static int a; static public int b;</source>

1. From inside a static method, you cannot call instance methods or instance fields because they only exist after you create an object.
2. You can access other static methods or fields from a static method.
3. You can only declare a static variable in a class level.
4. You cannot declare local static variables even if the method is static.

Demonstrates Static nested Classes

   <source lang="java">

/*

*     file: StaticNestedClassDemo.java
*  package: oreilly.hcj.nested
*
* This software is granted under the terms of the Common Public License,
* CPL, which may be found at the following URL:
* http://www-124.ibm.ru/developerworks/oss/CPLv1.0.htm
*
* Copyright(c) 2003-2005 by the authors indicated in the @author tags.
* All Rights are Reserved by the various authors.
*
########## DO NOT EDIT ABOVE THIS LINE ########## */

/**

* Demonstrates Static nested Classes.
* 
* @author 
  * @version $Revision: 1.5 $
  */
 private static class SomeOtherClass {
   /**
    * a demo method.
    */
   public void someMethod() {
     System.out.println("Protect me!");
   }
 }

} /* ########## End of File ########## */</source>

Demonstrate static variables, methods, and blocks.

   <source lang="java">

class UseStatic {

 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);
 }
  
 static {
   System.out.println("Static block initialized.");
   b = a * 4;
 }
  
 public static void main(String args[]) {
   meth(42);
 }

}</source>

Initializer for final static field

   <source lang="java">

public class ClassInitializer7 {

  final static int classField;
  static
  {
     classField = 29;
  }
  public static void main (String [] args)
  {
     System.out.println (classField);
  }

}</source>

Inside main( ), the static method callme( ) and the static variable b are accessed outside of their class.

   <source lang="java">

class StaticDemo {

 static int a = 42;
 static int b = 99;
 static void callme() {
   System.out.println("a = " + a);
 }

}

class StaticByName {

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

}</source>

Reference inner static class

   <source lang="java">

class MyClassesDemo {

 public static void main(String[] args) {
   MyClass tlc = new MyClass();
   MyClass.NestedMyClass ntlc;
   ntlc = new MyClass.NestedMyClass();
 }

} class MyClass {

 private int i;
 private static String name = "MyClass";
 {
   System.out.println("Assigning 1 to i");
   i = 1;
 }
 static class NestedMyClass {
   int j;
   {
     System.out.println("Assigning 2 to j");
     j = 2;
     System.out.println(name);
   }
 }

}</source>

reference static field after declaration

   <source lang="java">

public class ClassInitializer3 {

 static int classField1 = 1;
 static int classField2 = 1 + classField1;
 public static void main(String[] args) {
   System.out.println(classField1);
   System.out.println(classField2);
 }

}</source>

Static field, constructor and exception

   <source lang="java">

public class Main {

 static Bar bar;
 static {
   try {
     bar = new Bar();
   } catch (Exception e) {
     e.printStackTrace();
   }
 }
 public static void main(String[] argv) {
   System.out.println(bar);
 }

} class Bar {

 public Bar() throws Exception {
 }
 public String toString() {
   return "Bar";
 }

}</source>

Static Members

1. Static members are not tied to class instances.
2. Static members can be called without having an instance.

The out field in java.lang.System is static.

   <source lang="java">

public class MainClass {

 public static void main() {
   System.out.println("123");
 }

}</source>

the method main(the entry point to a class) is static because it must be called before any object is created.

static section Initializer and logic

   <source lang="java">

public class ClassInitializer6 {

 static int classField = 3;
 static {
   System.out.println(" : " + classField);
   classField = 1;
   for (int i = 2; i < 6; i++)
     classField *= i;
 }
 static {
   System.out.println(" = " + classField);
 }
 public static void main(String[] args) {
   System.out.println(classField);
 }

}</source>

static section of Initializer

   <source lang="java">

public class ClassInitializer5 {

 static String tz;
 static {
   java.util.Properties p = System.getProperties();
   p.list(System.out);
   tz = p.getProperty("user.timezone");
   if (tz.equals(""))
     tz = "Default";
 }
 public static void main(String[] args) {
   System.out.println("timezone = " + tz);
 }

}</source>