Static Initialization Block in Java

Instance variables are initialized using initialization blocks. However, the static initialization blocks can only initialize the static instance variables. These blocks are only executed once when the class is loaded. There can be multiple static initialization blocks in a class that is called in the order they appear in the program.

A program that demonstrates a static initialization block in Java is given as follows:

Example

 Live Demo

public class Demo {
   static int[] numArray = new int[10];
   static {
      System.out.println("Running static initialization block.");
      for (int i = 0; i < numArray.length; i++) {
         numArray[i] = (int) (100.0 * Math.random());
      }
   }
   void printArray() {
      System.out.println("The initialized values are:");
      for (int i = 0; i < numArray.length; i++) {
         System.out.print(numArray[i] + " ");
      }
      System.out.println();
   }
   public static void main(String[] args) {
      Demo obj1 = new Demo();
      System.out.println("For obj1:");
      obj1.printArray();
      Demo obj2 = new Demo();
      System.out.println("\nFor obj2:");
      obj2.printArray();
   }
}

Output

Running static initialization block.
For obj1:
The initialized values are:
40 75 88 51 44 50 34 79 22 21

For obj2:
The initialized values are:
40 75 88 51 44 50 34 79 22 21