Java 等于方法

Question

我正在编写一个程序来销售和购买游戏。我有 3 个 classes：Main、Person 和 Game。我想要它做什么：检查 (Game g) 是否已经在 (ArrayList games) 中，基本上检查相同的值。如果是，那么它应该 return 为真。如果为假，则应 return 为假。我怎样才能做到这一点？

我的问题：对于 p1.koop(g3) 它仍然说它成功了。但是，g2 和 g3 是相同的。因此应该不会成功。

我的主要：

package week3.practicum;

import java.time.LocalDate;  
public class Practicum2 {   
    public static void main(String[] args) {     
    int releaseJaar1 = LocalDate.now().getYear() - 1; // 1 jaar geleden     
    int releaseJaar2 = LocalDate.now().getYear() - 2; // 2 jaar geleden  

    Game g1 = new Game("Just Cause 3", releaseJaar1, 49.98);     
    Game g2 = new Game("Need for Speed: Rivals", releaseJaar2, 45.99);     
    Game g3 = new Game("Need for Speed: Rivals", releaseJaar2, 45.99);  
    Persoon p1 = new Persoon("Eric", 200.0);     
    Persoon p2 = new Persoon("Hans", 55.0);     
    Persoon p3 = new Persoon("Arno", 185.0);  
    System.out.println("p1 koopt g1:" + (p1.koop(g1) ? "" : " niet") + " gelukt");  
    System.out.println("p1 koopt g2:" + (p1.koop(g2) ? "" : " niet") + " gelukt");     
    System.out.println("p1 koopt g3:" + (p1.koop(g3) ? "" : " niet") + " gelukt");     
    System.out.println("p2 koopt g2:" + (p2.koop(g2) ? "" : " niet") + " gelukt");     
    System.out.println("p2 koopt g1:" + (p2.koop(g1) ? "" : " niet") + " gelukt");     
    System.out.println("p3 koopt g3:" + (p3.koop(g3) ? "" : " niet") + " gelukt");     
    System.out.println("\np1: " +p1+ "\n\np2: " +p2+ "\n\np3: " +p3+ "\n");  

    System.out.println("p1 verkoopt g1 aan p3:"+(p1.verkoop(g1, p3) ? "" : " niet")+" gelukt");     
    System.out.println("p2 verkoopt g2 aan p3:"+(p2.verkoop(g2, p3) ? "" : " niet")+" gelukt");     
    System.out.println("p2 verkoopt g1 aan p1:"+(p2.verkoop(g1, p1) ? "" : " niet")+" gelukt");     
    System.out.println("\np1: " +p1+ "\n\np2: " +p2+ "\n\np3: " +p3+ "\n");   } }

这是我的人class:

package week3.practicum;
import java.util.ArrayList;

public class Persoon {
    private String naam;
    private Double budget;
    private ArrayList<Game> games;
    private Game gameObj;

    public Persoon(String nm, Double bud){
        naam = nm;
        budget = bud;
        games = new ArrayList<Game>();
    }

    public boolean koop(Game g){
        Double huidW = g.huidigeWaarde();
        if (budget > huidW && games.equals(g) == false){
            games.add(g);
            budget = budget - huidW;
            return true;
        }
        else{return false;}
    }

    public boolean verkoop(Game g, Persoon koper){
        Double huidW = g.huidigeWaarde();

        if (koper.budget > huidW){
            koper.budget = koper.budget = huidW;
            budget = budget + huidW;
            koper.games.add(g);
            games.remove(g);
            return true;
        }
        else{
            return false;
        }
    }

    public String toString(){
        String s = naam + " heeft een budget van " +  budget + " en bezit de volgende games:\n";
        for (Game gam: games){
            s += gam;
        }
        return s;
    }
}

这是我在游戏中的 equals 方法 class。

package week3.practicum;

public class Game {
    private String naam;
    private Integer releaseJaar;
    private Double nieuwprijs;

    public Game(String nm, Integer rJ, Double nwpr){
        naam = nm;
        releaseJaar = rJ;
        nieuwprijs = nwpr;
    }

    public String getNaam(){
        return naam;
    }

    public Double huidigeWaarde(){
        Double huidigeprijs = 0.0;
        if (releaseJaar == 2016){
            huidigeprijs = nieuwprijs * 0.7;
        }
        else if (releaseJaar == 2015){
            huidigeprijs = nieuwprijs * 0.7 * 0.7;
        }
        else{
            huidigeprijs = nieuwprijs;
        }

        return huidigeprijs;
    }

  public boolean equals(Object andereObject) {     
      boolean gelijkeObjecten = false; // blijft false tenzij:  

    if (andereObject instanceof Game) {       
        Game andereGame = (Game) andereObject;  

      if (this.naam.equals(andereGame.naam)){ 
        gelijkeObjecten = true;       
        }
      }     

    return gelijkeObjecten;   }

    public String toString(){
        String s = naam + ", uitgegeven in " + releaseJaar + "; nieuwprijs: " + nieuwprijs + " nu voor: " + huidigeWaarde() + "\n";
        return s;
    }

}

Answer 1

您没有以任何方式调用 equals 方法。
满足您的初始需求：
1- 创建一个采用 2 个参数的私有方法：1- 游戏 ArrayList 和 2 您要检查的游戏。稍后 for 循环并检查游戏是否存在 return false.

private boolean doesGameExist(ArrayList gameList, Game gameToAdd){
    for (int i=0; i<gameList.size(); i++){
          if (gameList.get(i).equals(gameToAdd)){
               return true; //the game already exists
          }
    }
   return false; ///the game does not exist
 }

而不是在将新游戏添加到数组列表之前调用此函数。

Answer 2

games.equals(g) == false 除了不需要将 boolean 与 boolean 进行比较以将 boolean 转换为 boolean 这一事实之外，您正在比较 List 到 Game，永远不可能是 true.

Java 等于方法

Java Equals Method

java

equals