Using Initialization Blocks: static initialization block : Initialization Block « Class Definition « Java Tutorial

1. Java Tutorial
2. Class Definition
3. Initialization Block

1. A block defined using the keyword static.
2. Executed once when the class is loaded.
3. Can initialize only static data members of the class.

public class MainClass {
  static int[] values = new int[10];

  static {
    System.out.println("Running initialization block.");
    for (int i = 0; i < values.length; i++) {
      values[i] = (int) (100.0 * Math.random());
    }
  }

  void listValues() {
    for (int value : values) {
      System.out.println(value);
    }
  }

  public static void main(String[] args) {
    MainClass example = new MainClass();
    System.out.println("\nFirst object:");
    example.listValues();

    example = new MainClass();
    System.out.println("\nSecond object:");
    example.listValues();
  }
}

Running initialization block.

First object:
58
22
49
75
1
35
76
19
27
63

Second object:
58
22
49
75
1
35
76
19
27
63