java和继承构造函数

Question

我有一个名为 Item 的类通过以下方式完成

public class Item {


private static int nextId = 0;
private double xCoord, yCoord; //location
private double length, height; // define size of item
private String spriteImage;
private Tank tank;
private String id;


protected Item(double xCoord, double yCoord, String spriteImage, double length, double height,  Tank tank) throws ItemException {
    setId("I"+nextId); 
    nextId++;   
    setLocation(xCoord,yCoord);
    setSpriteImage(spriteImage);        
    setLength(length);
    setHeight(height);      
    setTank(tank);
}


/**
 * Set this item's location.
 * 
 * @param xCoord the column coordinate.
 * @param yCoord the row coordinate.
 */
public void setLocation(double xCoord, double yCoord) {
    this.xCoord = xCoord;
    this.yCoord = yCoord;
}

public double getXCoord() {
    return xCoord;
}

public double getYCoord() {
    return yCoord;
}

public double getLength() {
    return length;
}

public void setLength(double length) throws ItemException{
    if(length<=0) {
        throw new ItemException("MSG_ERR_LENGTH_VALUE");
    }
    this.length = length;
}

public double getHeight() {
    return height;
}

public void setHeight(double height) throws ItemException{
    if(height<=0) {
        throw new ItemException("MSG_ERR_HEIGHT_VALUE");
    }
    this.height = height;
}

public void setSpriteImage(String spriteImage) {

    this.spriteImage = spriteImage;
}

public String getSpriteImage() {        
    return spriteImage;
}

public String getId() {
    return id;
}

protected void setId(String id) {
    this.id = id;
}

public Tank getTank() {
    return tank;
}

public void setTank(Tank tank){
    if(tank!=null) {
        if(!tank.getItems().contains(this)) {
                tank.getItems().add(this);
        }
    }

    if(this.tank!=null) {
        try{
            this.tank.removeItem(this);
        }catch(Exception e) {
            //removeItem: El item no existe ya en el tanque
        }
    }

    this.tank = tank;
}


@Override
public String toString() {
    StringBuilder str = new StringBuilder("(" + getXCoord() +",  "+ getYCoord() +") ");

    str.append(getId() + " ");
    str.append(getLength() + " ");
    str.append(getHeight() + " ");
    str.append((getTank()!=null)?getTank().getName():"No tank");
    return str.toString();
}
}

我的问题是我必须实现两个类，其中一个继承自 Items，他们问我：这个类只有一个构造函数，它将与 参数。这些的顺序是：xCoord、yCoord、length、 高度，能量和坦克。 spriteImage 的值将始终是 相同：“./images/food/seed.png” 我实现如下

public class Food extends Item {

double speed=1;
boolean eaten;
int energy;


protected Food(double xCoord, double yCoord, String spriteImage,  double length, double height,int energy, Tank tank)
        throws Exception {
    super(xCoord, yCoord, spriteImage, length, height, tank);   
    setSpeed(speed);
    setEnergy(energy);
    setSpriteImage("./images/food/seed.png");
}

另一个类是一样的，他们问我这个类将有一个构造函数并且将是 带参数，其顺序为：xCoord, yCoord, 长度，高度和坦克。 spriteImage 的值将始终是 相同：“./images/submarine/submarine.png”

public class SubmarineToys extends Item{


double speed=1;
boolean facingRight=true;
double thresholdReverse=0.0003;

protected SubmarineToys(double xCoord, double yCoord, String spriteImage, double length, double height, Tank tank)
        throws ItemException {
    super(xCoord, yCoord, spriteImage, length, height, tank);
    setSpriteImage("./images/submarine/submarine.png");     
}

我的问题是我无法让构造函数在两个类中都要求我只拥有告诉我的参数。

根据超类的不同，构造函数总是在 Super() 中为我创建来自 Item 的参数，但他们要求我只有他们要求的参数，这意味着从超类的构造函数。

某种方式？

项目类不能是抽象的吗？

Answer 1

您可以简单地从孩子的 ctors 中省略 spriteImage。 结果应该是这样的：

public class Food extends Item {
   private static String foodSpriteImage = "./images/food/seed.png";
   private double speed=1;
   private boolean eaten;
   private int energy;

   // Child Ctor needs to be public.
   public Food(double xCoord, 
                  double yCoord, 
                  double length, 
                  double height,
                  int energy, 
                  Tank tank)
        throws Exception {
       super(xCoord, yCoord, foodSpriteImage , length, height, tank);   
       setEnergy(energy);
   }
}

Answer 2

您也可以忽略 spriteImage 参数并使用常量字符串调用 super()：

protected Food(double xCoord, double yCoord, String spriteImage, double length, double height, int energy, Tank tank) throws Exception {
    super(xCoord, yCoord, "./images/food/seed.png", length, height, tank);
    //                         ↑ here we put our default value instead of the spriteImage parameter
    setSpeed(speed);
    setEnergy(energy);
}

然后我们可能会删除spriteImage-参数：

protected Food(double xCoord, double yCoord, double length, double height, int energy, Tank tank) {...}