奇怪的Java语法--内部类的继承

因为内部内的构造器必须连接到指向外围类对象的引用，所以在继承内部类的时候，事情会变得有点复杂。问题在于，那个指向外国类对象的“秘密的”引用必须被初始化，而在导出类中不再存在可连接的默认对象。要解决这个问题，必须使用特殊的语法来明确说清它们之间的关联：(摘抄自Thinking In Java Fourth Edition)

package edu.dlut.zxf.test;

class OutClass {
    public class InnerClass {
        public InnerClass() { }
    }
}

class InheritInnerClass extends OutClass.InnerClass {
    //public InheritInnerClass() { } //不能通过编译

    public InheritInnerClass(OutClass out) {        
        out.super();
    }
}

public class Test {
    public static void main(String[] args) {
        OutClass out = new OutClass();
        InheritInnerClass inherit = new InheritInnerClass(out);
        System.out.println(inherit);
    }
}

再看一例：

package edu.dlut.zxf.test;

class OutClass {
    public class InnerClass {
        private String s;
        public InnerClass(String s) {
            this.s = s;
        }
        
        public String toString() {
            return s;
        }
    }
}

class InheritInnerClass extends OutClass.InnerClass {
    //public InheritInnerClass() { } //不能通过编译
   
    public InheritInnerClass(OutClass out) {        
        out.super("hello, world");
        System.out.println(this);
    }
}

public class Test {
    public static void main(String[] args) {
        OutClass out = new OutClass();
        InheritInnerClass inherit = new InheritInnerClass(out);
        System.out.println(inherit);
    }
}