java使用類之前的準備工作

package com.test.testtypeinfo;
import java.util.*;


class Initable {
  static final int staticFinal = 47;
  static final int staticFinal2 =
    ClassInitialization.rand.nextInt(1000);
  static {
    System.out.println("Initializing Initable");
  }
}


class Initable2 {
  static int staticNonFinal = 147;
  static {
    System.out.println("Initializing Initable2");
  }
}


class Initable3 {
  static int staticNonFinal = 74;
  static {
    System.out.println("Initializing Initable3");
  }
}


public class ClassInitialization {
  public static Random rand = new Random(47);
  public static void main(String[] args) throws Exception {
    Class initable = Initable.class;
    System.out.println("After creating Initable ref");
    // Does not trigger initialization:
    System.out.println(Initable.staticFinal);
    System.out.println("-----------------------");
    // Does trigger initialization:
    System.out.println(Initable.staticFinal2);
    System.out.println("-----------------------");
    // Does trigger initialization:
    System.out.println(Initable2.staticNonFinal);
    System.out.println("-----------------------");
    Class initable3 = Class.forName("com.test.testtypeinfo.Initable3");
    System.out.println("After creating Initable3 ref");
    System.out.println(Initable3.staticNonFinal);
  }
} /* Output:
After creating Initable ref
47
-----------------------
Initializing Initable
258
-----------------------
Initializing Initable2
147
-----------------------
Initializing Initable3
After creating Initable3 ref
74
*///:~