java - 在实现另一个类接口(interface)的类中使用属​​性

Question

大家好，我正在尝试使用我的 Fish 类 中的属性，它在我的 Fisher 类 中实现了一个名为 Catchable 的接口(interface)，这可能吗，或者是否有我不理解的接口(interface)的某些部分。因为我认为我们被允许在一个由接口(interface)实现的类中使用属​​性，在另一个类中，但是我一直错误地说:

Error: cannot find symbol
  symbol:   variable weight
  location: variable item of type Catchable

Error: cannot find symbol
  symbol:   variable size
  location: variable item of type Catchable

Error: cannot find symbol
  symbol:   variable weight
  location: variable item of type Catchable .

如有任何帮助或建议，我们将不胜感激!

如果需要，这是我的 Catchable 界面:

public interface Catchable
{
  public float getWeight();
  public boolean isDesirableTo(Fisher f);
}

我的 Fish 类 实现了 Catchable 接口(interface)

public abstract class Fish implements Catchable
{
    // Any fish below this size must be thrown back into the lake
    public static int  THROW_BACK_SIZE = 18; 
    public static float WEIGHT_LIMIT = 10;

    protected float weight;
    protected int  size;

    public Fish(int aSize, float aWeight) 
    {
        size = aSize;
        weight = aWeight;
    }


    public boolean isDesirableTo(Fisher f) 
    {
        if(canKeep() && f.numThingsCaught < f.LIMIT && this.weight + f.sumOfWeight < WEIGHT_LIMIT)
        {
          return true;
        }
        else
        {
        return false;
        }
    }

    public abstract boolean canKeep(); 

    public int getSize() { return size; }
    public float getWeight() { return weight; }


    public String toString () 
    {
        return ("A " + size + "cm " + weight +  "kg " + this.getClass().getSimpleName());
    }

}

最后是我的Fisher 类

import java.util.*;

public class Fisher     
{
  private String name;
  private Catchable [] thingCaught;
  public int numThingsCaught; 
  private int keepSize;
  public float  sumOfWeight;
  public static int LIMIT = 10;

  public String getName() 
  {
    return this.name;
  }

  public int getNumThingsCaught()
  {
    return this.numThingsCaught;
  }

  public int getKeepSize()
  {
    return this.keepSize;
  }


  public Fisher(String n, int k)
  {
    name = n;
    keepSize = k;
  }

  public String toString()
  {
    return(this.name + " with " + this.numThingsCaught + " fish");
  }
  private ArrayList<Catchable> thingsCaught = new ArrayList<Catchable>();


  public void keep(Catchable item) 
  {
    if(this.numThingsCaught < LIMIT)
    {
      thingsCaught.add(item);
      numThingsCaught++;
      sumOfWeight += item.weight;
    }
  }

  public boolean likes(Catchable item)
  {
    if(item.size >= this.keepSize)
    {
      return true;
    }

    else 
    {
      return false;
    }
  }

  public void listThingsCaught() 
  {
    System.out.println(this.toString());

    for(Catchable item : thingsCaught)
    {
      System.out.println(item.toString());
    }
  }

  public void goFishingIn(Lake lake)
  {
    Catchable item = lake.catchSomething();

    if(likes(item))
    {
      this.keep(item);
    }
    else
    {
      lake.add(item);
    }
  }

  public void giveAwayFish(Fisher fisher, Lake lake)
  {
    for(Catchable item : thingsCaught)
    {
      if(fisher.likes(item))
      {
        fisher.keep(item);
      }
      else
      {
        lake.add(item);
      }
      sumOfWeight -= item.weight;
    }
    thingsCaught.clear();
    this.numThingsCaught = 0;

  }

}

Answer 1

问题是以下几行:

• 保持():

  sumOfWeight += item.weight;
  

• likes():

  if(item.size >= this.keepSize)
  

• giveAwayFish():

  sumOfWeight -= item.weight;
  

在每种情况下，item 都是 Catchable 类型，而 Catchable 没有 size 或 权重字段。您需要做的是调用 item.getWeight() 而不是 item.weight 并将 getSize() 方法添加到 Catchable ，并调用 item.getSize() 而不是 item.size:

• 可捕获:

  public interface Catchable
  {
    public float getWeight();
    public int getSize();
    public boolean isDesirableTo(Fisher f);
  }
  

• 保持():

  sumOfWeight += item.getWeight();
  

• likes():

  if(item.getSize() >= this.keepSize)
  

• giveAwayFish():

  sumOfWeight -= item.getWeight();
  

您不必修改 Fish，因为它已经实现了 getSize()。 而且您真的应该使用像 Eclipse 这样的 IDE，因为它可以实时显示您的错误位置。