Java类变量的初始化顺序是什么?

在Java中,类变量在 following order

2. 该类的所有静态变量都设置为 default values
3. 静态变量和静态初始化块,按声明顺序。
4. 超类的实例变量
5. 该类的所有实例变量都设置为 默认值
6. 实例变量和实例级初始化块,按声明顺序

因此,考虑到以下代码:

class Test
  extends TestSuper
{
  final int ti1;
  final int ti2 = counter ++;
  { ti1 = counter ++; }
  static final int ts1;
  static final int ts2 = counter ++;
  static { ts1 = counter ++; }

  public static void main(String[] argv) {
    Test test1 = new Test();
    printTest(test1);
    Test test2 = new Test();
    printTest(test2);
  }
  private static void printTest(Test test) {
    System.out.print("ss2 = " + test.ss2);
    System.out.print(", ss1 = " + test.ss1);
    System.out.print(", ts2 = " + test.ts2);
    System.out.println(", ts1 = " + test.ts1);
    System.out.print("si2 = " + test.si2);
    System.out.print(", si1 = " + test.si1);
    System.out.print(", ti2 = " + test.ti2);
    System.out.println(", ti1 = " + test.ti1);
    System.out.println("counter = " + test.counter);
  }
}

class TestSuper
{
  static int counter = 0;
  final int si1;
  final int si2 = counter ++;
  { si1 = counter ++; }
  static final int ss1;
  static final int ss2 = counter ++;
  static { ss1 = counter ++; }
}

然后我们得到以下输出:

ss2 = 0, ss1 = 1, ts2 = 2, ts1 = 3
si2 = 4, si1 = 5, ti2 = 6, ti1 = 7
counter = 8
ss2 = 0, ss1 = 1, ts2 = 2, ts1 = 3
si2 = 8, si1 = 9, ti2 = 10, ti1 = 11
counter = 12

现在,关于第二个问题,字段的重新排序是否会改变类的行为。是的,通过对字段重新排序,可以更改字段的初始化顺序。现在,在所有字段都是独立的特定情况下,这不会影响观察到的行为,但是只要字段不是独立的,例如在上面的代码中,那么对字段重新排序可能会更改其初始值。

例如,如果三行:

  static final int ss1;
  static final int ss2 = counter ++;
  static { ss1 = counter ++; }

  static final int ss1;
  static { ss1 = counter ++; }
  static final int ss2 = counter ++;

然后输出将更改为:

ss2 = 1, ss1 = 0, ts2 = 2, ts1 = 3
si2 = 4, si1 = 5, ti2 = 6, ti1 = 7
counter = 8

ss2 ,及 ss1

原因是该行为在 Java Language Specification