转-Cannot refer to an instance field arg while explicitly invoking a constructor

编译失败：

Cannot refer to an instance field arg while explicitly invoking a constructor  调用方法是不能引用一个实例变量

 1 package arkblue.lang.javapuzzler.n53;
 2
 3 class Thing {
 4     public Thing(int i) {
 5
 6     }
 7 }
 8
 9 public class MyThing extends Thing {
10     private final int arg;
11
12     public MyThing() {
13         super(arg = Math.round(12L)); //编译失败
14     }
15
16 }

解决办法:使用了交替构造器调用机制（alternate constructor invocation）

在这个私有构造器中，表达式SomeOtherClass.func()的值已经被捕获到了变量i中，并且它可以在超类构造器返回之后存储到final类型的域arg中

 1 class SomeOtherClass {
 2     static int func() {
 3         return Math.round(12L);
 4     }
 5 }
 6
 7 public class MyThing extends Thing {
 8     private final int arg;
 9
10     public MyThing() {
11         this(SomeOtherClass.func());
12     }
13
14     private MyThing(int i) {
15         super(i);
16         arg = i;
17     }
18 }