Java:扩展内部类

Question

我试图理解在Java中扩展内部类.我已经阅读过,但没有找到我的问题.所以这里......

我有...

public class Pie{
    protected Slice[] slices;

    // Pie constructor
    public Pie(int n){
         sliceGenerator(n)
    }

    private void sliceGenerator(int n){
         slices = new Slice[n];
         final float sweepAngle = 360.0f/(float)n;
         float startAngle = 0;
         for (int i=0;i<n;i++){ 
             slices[i] = new Slice(startAngle);
             startAngle += sweepAngle;
         }
    }

    @Override
    public String toString(){
         for (Slice s:slices){  
             s.toString();
         }
    }

    // Inner class...
    public class Slice{
        public Slice(float startAngle){
             //set some private fields based on startAngle and generic pie 
        }

        @Override
        public String toString(){
             return **string based on private fields**
        }
    }
}

然后我扩展这个......

public class ApplePie extends Pie{
    protected Slice[] slices;

    // Apple Pie constructor
    public ApplePie(int n){
         super(n);
    }

    // Inner class...
    public class Slice extends Pie.Slice{
        public Slice(float startAngle){
            super(startAngle);
            //set some **additional** private fields based on startAngle **specific to apple pie** appleness or something
        }

        @Override
        public String toString(){
             return **string based on apple pie specific private fields**
        }
    }
}

现在,当我制作一个Apple派并调用其toString方法时,就像这样......

ApplePie ap = new ApplePie(8);
System.out.println(ap.toString());

我没有获得有关苹果派切片的信息,但有关馅饼切片的信息.它忽略了我的toString覆盖,或者更可能忽略了我的苹果派Slice.如何安排苹果派切片参考ApplePie？

任何帮助非常感谢!对不起馅饼参考 - 这是我正在使用的实际课程......

Answer 1

我已经更改了您的代码以满足您的要求。

您的超类Pie即将创建 的新实例Slice，但子类 ApplePie 的 Slice 不会覆盖Slice其超类的方法。

我添加了下面的函数以使子类能够创建自己的Slice.

protected void newSliceArray(int n) {
    slices = new Slice[n];
}

protected Slice newSlice(float startAngle) {
    return new Slice(startAngle);
}

馅饼.java：

public class Pie {
  private int a = 1;
  protected Slice[] slices;

  // Pie constructor
  public Pie(int n) {
    sliceGenerator(n);
  }

  private void sliceGenerator(int n) {
    newSliceArray(n);
    final float sweepAngle = 360.0f / n;
    float startAngle = 0;
    for (int i = 0; i < n; i++) {
      slices[i] = newSlice(startAngle);
      startAngle += sweepAngle;
    }
  }

  protected void newSliceArray(int n) {
    slices = new Slice[n];
  }


  protected Slice newSlice(float startAngle) {
    return new Slice(startAngle);
  }

  @Override
  public String toString() {
    String t = "";
    for (Slice s : slices) {
      t += s.toString();
    }
    return t;
  }

  // Inner class...
  public class Slice {
    public Slice(float startAngle) {
      // set some private fields based on startAngle and generic pie
    }

    @Override
    public String toString() {
      return "" + a;
    }
  }
}

苹果派.java：

public class ApplePie extends Pie {
  private int b = 2;

  // protected Slice[] slices;

  // Apple Pie constructor
  public ApplePie(int n) {
    super(n);
  }

  protected void newSliceArray(int n) {
    slices = new Slice[n];
  }

  protected Slice newSlice(float startAngle) {
    return new Slice(startAngle);
  }

  // Inner class...
  public class Slice extends Pie.Slice {
    public Slice(float startAngle) {
      super(startAngle);
      // set some **additional** private fields based on startAngle **specific to apple pie**
      // appleness or something
    }

    @Override
    public String toString() {
      return b + "";
    }
  }
}

测试：

public static void main(String[] args) {
    ApplePie ap = new ApplePie(8);
    System.out.println(ap.toString());
}

代码将打印 22222222