Question

所以，我们有一个自行车超级课程，有节奏0和3子类。我想要＆＃34; trotineta＆＃34; sbuclass有cadence 5而其他2个子类cadence仍为0。为什么这不起作用？

    class Trotineta extends Bicycle{   
        Bicycle.cadence = 5;
    }

Answer 1

您还没有显示Bicycle.cadence的定义，但根据语法，我假设它是静态成员。如果更改基类的静态成员，则此更改将影响所有子类的所有实例，因为静态成员对于该类的所有实例都具有单个值。

现在，如果cadence不是静态的，你可以在Trotineta的构造函数中给它一个不同的值（假设子类可以访问该成员）。

public Trotineta ()
{
    cadence = 5;
}

但这会有点浪费，因为Bicycle的每个实例都有自己的cadence成员。

Answer 2

您可以创建getter和setter，也可以只使用word super

public class TestONE extends TestTWO {
    {
        super.gg = 4;
    }
    public static void main(String[] args) {
        System.err.println(new TestONE().gg);
    }
}
class TestTWO {
    static int gg = 0;
}

或

public class TestONE extends TestTWO {
        public static void main(String[] args) {
            TestONE.setGg(5);
            System.err.println(new TestTWO().gg);
        }
    }
class TestTWO {
        protected static int gg = 0;

        public static int getGg() {
            return gg;
        }

        public static void setGg(int gg) {
            TestTWO.gg = gg;
        }   
    }

Answer 3

    class Bicycle{ 
                  int cadence = 0;
                  /* since no access modifier is mentioned, by default cadence becomes 
                  package private ie; it cannot be accessed outside the package 
                  in which it is defined now*/  
                 }

    class Trotineta extends Bicycle{
                                    Bicycle.cadence = 5; 
                                    /* you cannot do this as cadence is not a static 
                                    attribute of class Bicycle*/
                                    }

//以下是可能的解决方案之一

   class Trotineta extends Bicycle{
             /*below code can also be written in a method but not outside as you have
               written in your example code*/
                                    { 
                                     this.cadence = 5; 
                                    //here 'this' is the current instance of Trotineta 
                                    } 
                                  }

为什么我无法更改子类值

3 个答案: