使用Collections.sort（）時，它排序並打印散列碼

Question

我正在使用一個使用ArrayList包含新實例並使用Collections.sort（）方法使用可比接口的示例。我不知道它爲什麼打印出散列碼，當它排序和我的代碼中的錯誤。任何人都可以找出錯誤並詳細解釋我。

SortFruitObject.java

import java.util.*; 
public class SortFruitObject{ 
    public static void main(String[] args){ 
     ArrayList<Fruit> frui = new ArrayList<Fruit>(); 

     frui.add(new Fruit("Pine", "PineDesc", 500)); 
     frui.add(new Fruit("Apple", "AppleDesc", 400)); 
     frui.add(new Fruit("Banana", "BananaDesc", 450)); 
     frui.add(new Fruit("JackFruit", "JackFruitDesc", 300)); 

     Collections.sort(frui); 
     System.out.println(frui); 
    } 
} 

Fruit.java

import java.io.*; 
import java.util.*; 
public class Fruit implements Comparable<Fruit>{ 
    private String fruitName; 
    private String fruitDesc; 
    private int fruitQuantity; 

    public int compareTo(Fruit f){ 
     return fruitName.compareTo(f.getFruitName()); 
    } 

    public Fruit(String fruitName, String fruitDesc, int fruitQuantity){ 
     this.fruitName = fruitName; 
     this.fruitDesc = fruitDesc; 
     this.fruitQuantity = fruitQuantity; 
    } 
    public void setFruitName(String fruitName){ 
     this.fruitName = fruitName; 
    } 
    public void setFruitDesc(String fruitDesc){ 
     this.fruitDesc = fruitDesc; 
    } 
    public void setFruitQuantity(int fruitQuantity){ 
     this.fruitQuantity = fruitQuantity; 
    } 
    public String getFruitName(){ 
     return fruitName; 
    } 
    public String getFruitDesc(){ 
     return fruitDesc; 
    } 
    public int getFruitQuantity(){ 
     return fruitQuantity; 
    } 
} 

輸出：

[Fruit@36422510, Fruit@308f5944, Fruit@132d9844, Fruit@1667a232] 

Answer 1

你需要ŧ O強制toString()方法來打印輸出漂亮的，默認情況下它認爲對象的toString（），這是實現像

public String toString() { 
     return getClass().getName() + "@" + Integer.toHexString(hashCode()); 
    } 

等輸出