无法调用HashSet的内类的方法

Question

我所试图做的是

类总结在危险的影响值，例如，它会经过乘客的名单，发现危险并获得影响从它的金额。然后总结所有危害的总体影响并将该价值返还给我。

下面我有洞穴类，危险级别和摘要乘员类。

向洞穴添加危险时，它成为HashSet中的占有者。 当试图通过getImpact（）方法获取能量级别时，该方法无法访问，因为它处于危险中而不是占用。

我有两个其他职业也延伸占用者。 玩家和商品。

添加到HashSet中时，我找不到一种方法将危险作为危险类别，以便可以使用getImpact（）方法。

当添加到HashSet时，这也需要迎合其他类Player和Item。

---

public class Cave { 

HashSet<Occupant> occupants; 
private double impact; 

/** 
* Creat a new Cave instance with no occupants. 
*/ 
public Cave() 
{ 
    occupants = new HashSet<Occupant>(); 
} 

/** 
* Adds an occupant to a Cave if the occupant is not already there and 
* if cave currently has fewer than the maximum number of occupants. 
* @param occupant, the occupant to add 
* @return true if successfully added 
*/ 
public boolean addOccupant(Occupant occupant) { 
    boolean validNewOccupant = occupant != null; 
    boolean enoughRoom = occupants.size() < MAX_OCCUPANTS; 
    if (validNewOccupant && enoughRoom) { 
     validNewOccupant = occupants.add(occupant); 
    } 

    return validNewOccupant && enoughRoom; 
} 

/** 
* Gets the sum of the impact from all hazards in the cave 
* @returns hazardEnergyImpact 
*/ 
public double getHazardEnergyImpacts(){ 
    double energyImpact = 0.0; 
    for(Occupant occupant : occupants){ 
     if(occupant.toString() == "!"){ 
      energyImpact += occupant.getImpact(); 
     } 
    } 
    return energyImpact; 
} 
} 

---

public abstract class Occupant { 

private Address address; 
private String name; 

/** 
* Construct an occupant for a known address & name. 
* @ param row, row of address 
* @ param column, row of address. 
* @ param name, occupant's name 
*/ 
public Occupant(Address address, String name) { 
    this.address = address; 
    this.name = name; 
} 

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

---

public class Hazard extends Occupant { 

private String longDescription; 
private double impact; 

/** 
* Construct a hazard with know attributes 
* @param row 
* @param column 
* @param name 
* @param longDescription 
* @param impact 
*/ 
public Hazard(Address address, String name, String longDescription, double impact) { 
    super(address, name); 
    this.longDescription = longDescription; 
    this.impact = impact; 
} 

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

/** 
* gets impact amount 
* @returns impact 
*/ 
public double getImpact(){ 
    return this.impact; 
} 
} 

Answer 1

当遍历您occupants你可以检查，看看是否每个项目是Hazard像这样：

for(Occupant occupant : occupants){ 
    if(occupant instanceof Hazard){ 
     Hazard hazard = (Hazard) occupant; // now it's safe to cast 
     double impact = hazard.getImpact(); 
     // do what you want with impact 
    } 
} 

Answer 2

杰里米打败了我。

但是，instanceof并不总是最好的解决方案。但在这种情况下，这是一个解决方案。

我实际上建议在这里使用接口来代替使用抽象类的行为。但是，如果您必须使用抽象类，则更有效的方法是简单地创建要在子类中使用的抽象方法。您必须在每个孩子中都覆盖他们，但是您无需在每种情况下都实施它们。

Answer 3

我会在这里使用Visitor pattern。

public interface Occupant { 
    void interact(Player p); 
} 

public class Player { 
    public void handleInteraction(Hazard hazard) { 
    // add code here 
    } 
    public void handleInteraction(Person person) { 
    // add code here 
    } 
} 

public class Hazard implements Occupant { 
    public void interact(Player p) { 
    p.handleInteraction(this); 
    } 

    public double getImpact(){ 
    return this.impact; 
    } 
} 

Answer 4

另一种选择是将getImpact()方法添加到乘员，例如，

public double getImpact() { 
    return 0.0; 
} 

而Hazard的@Override实施getImpact()将只返回其impact实例变量，你已经拥有了它成立。然后，你的循环被简化为：

public double getHazardEnergyImpacts() { 
    double energyImpact = 0.0; 
    for(Occupant occupant : occupants) { 
     energyImpact += occupant.getImpact(); 
    } 
    return energyImpact; 
} 

如果您需要后解压到一个适当的抽象接口，这是一件好事现代IDE使其轻而易举。