Java uses internal classes to implement multiple inheritance

Example 1

public class Father {
    public int strong() {   
        // 强壮指数
        return 9;
    }
}

public class Mother {
    public int kind() {    
        // 友好指数
        return 8;
    }
}

public class Son {
    // 内部类继承Father类
    class Father_1 extends Father {
        public int strong() {
            return super.strong() + 1;
        }
    }
    class Mother_1 extends Mother {
        public int kind() {
            return super.kind() - 2;
        }
    }
    public int getStrong() {
        return new Father_1().strong();
    }
    public int getKind() {
        return new Mother_1().kind();
    }
}

public class Test {
    public static void main(String[] args) {
        Son son = new Son();
        System.out.println("Son 的强壮指数：" + son.getStrong());
        System.out.println("Son 的友好指数：" + son.getKind());
    }
}

Son 的强壮指数：10
Son 的友好指数：6