Java 值无法解析或不是字段

如果

this

和

moving

平铺具有相同的值，则方法

public boolean mergesWith（平铺移动）

返回

true

。但当我通过以下操作检查它们是否相同时：

if(this.value == temp.value){
    return true;
}

然后它显示了

温度值

上的错误，表示值无法解析或不是字段

我怎样才能解决这个问题

类TwoNTile：

package Game2048;

// Concrete implementation of a Tile. TwoNTiles merge with each other
// but only if they have the same value.

public class TwoNTile extends Tile {

    private int value;

    // Create a tile with the given value of n; should be a power of 2
    // though no error checking is done
    public TwoNTile(int n){
        value = n;
    }

    // Returns true if this tile merges with the given tile. "this"
    // (calling tile) is assumed to be the stationary tile while moving
    // is presumed to be the moving tile. TwoNTiles only merge with
    // other TwoNTiles with the same internal value.
    public boolean mergesWith(Tile moving){
        Tile temp = moving;
        if(this.value == temp.value){
            return true;
        }
        else{
            return false;
        }
    }

    // Produce a new tile which is the result of merging this tile with
    // the other. For TwoNTiles, the new Tile will be another TwoNTile
    // and will have the sum of the two merged tiles for its value.
    // Throw a runtime exception with a useful error message if this
    // tile and other cannot be merged.
    public Tile merge(Tile moving){

        return null;
    }

    // Get the score for this tile. The score for TwoNTiles are its face
    // value.
    public int getScore(){

        return -1;
    }

    // Return a string representation of the tile
    public String toString(){

        return "";
    }
}

package Game2048;

// Abstract notion of a game tile.
public abstract class Tile{
  // Returns true if this tile merges with the given tile. 
  public abstract boolean mergesWith(Tile other);

  // Produce a new tile which is the result of merging this tile with
  // the other. May throw an exception if merging is illegal
  public abstract Tile merge(Tile other);

  // Get the score for this tile.
  public abstract int getScore();

  // Return a string representation of the tile
  public abstract String toString();

}

类平铺：

package Game2048;

// Concrete implementation of a Tile. TwoNTiles merge with each other
// but only if they have the same value.

public class TwoNTile extends Tile {

    private int value;

    // Create a tile with the given value of n; should be a power of 2
    // though no error checking is done
    public TwoNTile(int n){
        value = n;
    }

    // Returns true if this tile merges with the given tile. "this"
    // (calling tile) is assumed to be the stationary tile while moving
    // is presumed to be the moving tile. TwoNTiles only merge with
    // other TwoNTiles with the same internal value.
    public boolean mergesWith(Tile moving){
        Tile temp = moving;
        if(this.value == temp.value){
            return true;
        }
        else{
            return false;
        }
    }

    // Produce a new tile which is the result of merging this tile with
    // the other. For TwoNTiles, the new Tile will be another TwoNTile
    // and will have the sum of the two merged tiles for its value.
    // Throw a runtime exception with a useful error message if this
    // tile and other cannot be merged.
    public Tile merge(Tile moving){

        return null;
    }

    // Get the score for this tile. The score for TwoNTiles are its face
    // value.
    public int getScore(){

        return -1;
    }

    // Return a string representation of the tile
    public String toString(){

        return "";
    }
}

package Game2048;

// Abstract notion of a game tile.
public abstract class Tile{
  // Returns true if this tile merges with the given tile. 
  public abstract boolean mergesWith(Tile other);

  // Produce a new tile which is the result of merging this tile with
  // the other. May throw an exception if merging is illegal
  public abstract Tile merge(Tile other);

  // Get the score for this tile.
  public abstract int getScore();

  // Return a string representation of the tile
  public abstract String toString();

}

---

在

平铺

类中，需要添加类变量

值

，如下所示：

package Game2048;

// Abstract notion of a game tile.
public abstract class Tile{

   //need to add instance variable
   int value; 

  // Returns true if this tile merges with the given tile. 
  public abstract boolean mergesWith(Tile other);

  // Produce a new tile which is the result of merging this tile with
  // the other. May throw an exception if merging is illegal
  public abstract Tile merge(Tile other);

  // Get the score for this tile.
  public abstract int getScore();

  // Return a string representation of the tile
  public abstract String toString();

}

---

首先：您可以执行以下操作：

public boolean mergesWith(Tile moving){
    return this.value == temp.value;
}

以获得更优雅的解决方案

Second：您需要将

值

变量添加到

平铺

类中

public abstract class Tile{
   // ...
   // add a value to Tile
   protected int value; 
   // ...
}

您已经扩展了

平铺
并添加了新字段。该字段不是
平铺
的字段，
平铺
不包含（看不到）它

基于以下评论：

package Game2048;

// Concrete implementation of a Tile. TwoNTiles merge with each other
// but only if they have the same value.

public class TwoNTile extends Tile {

    private int value;

    // Create a tile with the given value of n; should be a power of 2
    // though no error checking is done
    public TwoNTile(int n){
        value = n;
    }

    // Returns true if this tile merges with the given tile. "this"
    // (calling tile) is assumed to be the stationary tile while moving
    // is presumed to be the moving tile. TwoNTiles only merge with
    // other TwoNTiles with the same internal value.
    public boolean mergesWith(Tile moving){
        Tile temp = moving;
        if(this.value == temp.value){
            return true;
        }
        else{
            return false;
        }
    }

    // Produce a new tile which is the result of merging this tile with
    // the other. For TwoNTiles, the new Tile will be another TwoNTile
    // and will have the sum of the two merged tiles for its value.
    // Throw a runtime exception with a useful error message if this
    // tile and other cannot be merged.
    public Tile merge(Tile moving){

        return null;
    }

    // Get the score for this tile. The score for TwoNTiles are its face
    // value.
    public int getScore(){

        return -1;
    }

    // Return a string representation of the tile
    public String toString(){

        return "";
    }
}

package Game2048;

// Abstract notion of a game tile.
public abstract class Tile{
  // Returns true if this tile merges with the given tile. 
  public abstract boolean mergesWith(Tile other);

  // Produce a new tile which is the result of merging this tile with
  // the other. May throw an exception if merging is illegal
  public abstract Tile merge(Tile other);

  // Get the score for this tile.
  public abstract int getScore();

  // Return a string representation of the tile
  public abstract String toString();

}

在
Tile
中声明值时，无需再次在
TwoNTile
中声明。
您可以生成平铺对象，但不能使用构造函数

Tile t = new TwoNTile(...);

是有效的
平铺
对象。这样，您就可以实现已经尝试使用的逻辑

看看Java中的SO，或者。
您试图从没有属性的抽象类访问属性

你需要在更高的层次上进行切割

TwoNTile temp = (TwoNTile) moving;

我意识到这个抽象类可能有不止一个扩展，但是您需要将它切割到类层次结构中的最高级别，这样被铸造的类或它的后代就可以回答这个问题

更新的方法：

public boolean mergesWith(Tile moving){
    TwoNTile temp = (TwoNTile) moving;
    if(this.value == temp.value){
        return true;
    }
    else{
        return false;
    }
}

在类
Tile
中没有名为
value
的字段，您将
Tile
传递给方法，而不是
TwoNTile
，但是如果
Tile
类是
抽象的
并且无法创建对象，那么这是唯一的方法，即在
Tile
类中声明
int-value
@XP500您仍然可以从子类调用抽象类的构造函数。因此，您可以将
value
字段移动到抽象类，然后
TwoNTile
构造函数可以调用
super（value）
，但是如果
TwoNTile
扩展了
Tile
，为什么我必须这样做呢？还有别的办法吗@BlackHatSamuraibut如果我不能从
value
类中创建对象，我怎么知道
value
的值是什么@Aleksandar根据您编辑的评论，@Aleksandar，我是否应该只在
Tile
类中声明
protected int value
，就这样？@John Yes。试试看。：）您可以在TwoNTile中为该字段赋值（以及扩展平铺的其他字段），但声明是在平铺类中。