Java Tutorial - Java static final

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;
/*fromwww.java2s.com*/
 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 {/*fromwww.java2s.com*/
 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.