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  调用方法时不能引用一个实例变量

 

package arkblue.lang.javapuzzler.n53;

class Thing {
    public Thing(int i) {

    }
}

public class MyThing extends Thing {
    private final int arg;

    public MyThing() {
        super(arg = Math.round(12L)); //编译失败
    }

}

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

class SomeOtherClass {
    static int func() {
        return Math.round(12L);
    }
}

public class MyThing extends Thing {
    private final int arg;

    public MyThing() {
        this(SomeOtherClass.func());
    }

    private MyThing(int i) {
        super(i);
        arg = i;
    }
}