Java - static keyword

Static Variables

The static keyword is used to create variables that will exist independently of any instances created for the class. Only one copy of the static variable exists regardless of the number of instances of the class.

Static variables are also known as class variables. Local variables cannot be declared static.

Static Methods

The static keyword is used to create methods that will exist independently of any instances created for the class.

Static methods do not use any instance variables of any object of the class they are defined in. Static methods take all the data from parameters and compute something from those parameters, with no reference to variables.

Class variables and methods can be accessed using the class name followed by a dot and the name of the variable or method.

The static modifier is used to create class methods and variables, as in the following example −

Example

public class InstanceCounter {

   private static int numInstances = 0;

   protected static int getCount() {
      return numInstances;
   }

   private static void addInstance() {
      numInstances++;
   }

   InstanceCounter() {
      InstanceCounter.addInstance();
   }

   public static void main(String[] arguments) {
      System.out.println("Starting with " + InstanceCounter.getCount() + " instances");

      for (int i = 0; i < 500; ++i) {
         new InstanceCounter();
      }
      System.out.println("Created " + InstanceCounter.getCount() + " instances");
   }
}

Output

Starting with 0 instances
Created 500 instances

Following is another example, where we're accessing static method using object instead of class −

Example

public class InstanceCounter {

   private static int numInstances = 0;

   protected static int getCount() {
      return numInstances;
   }

   private static void addInstance() {
      numInstances++;
   }

   InstanceCounter() {
      InstanceCounter.addInstance();
   }

   public static void main(String[] arguments) {
      System.out.println("Starting with " + InstanceCounter.getCount() + " instances");

      for (int i = 0; i < 499; ++i) {
         new InstanceCounter();
      }
      InstanceCounter ic = new InstanceCounter();
      System.out.println("Created " + ic.getCount() + " instances");
   }
}

Output

Starting with 0 instances
Created 500 instances