MyClass不能转换为java.lang.Comparable：java.lang.ClassCastException [英] MyClass cannot be cast to java.lang.Comparable: java.lang.ClassCastException

问题描述

我的项目中的类（简化）：

我正在做一个java项目，我遇到这个问题，不知道如何解决它。 p>

  public class Item {
 
 private String itemID; 
私人整数价格; 
 
 public Integer getPrice（）{
 
 return this.price; 
 
} 
 
} 
 
 public class Store {
 
 private String storeID; 
 private String address; 
 
} 
 
 public class Stock {
 
 private Item item; 
私人店铺; 
 private整数itemCount; 
 
 public Integer getInventoryValue（）{
 
 return this.item.getPrice（）* this.itemCount; 
 
} 
} 
  

然后我尝试排序一个 ArrayList 的股票，所以我创建另一个类叫$ code> CompareByValue

  public class CompareByValue implements Comparator< Stock> {
 
 @Override 
 public int compare（stock stock1，stock stock2）{
 
 return（stock1.getInventoryValue（） -  stock2.getInventoryValue（））; 
 
} 
  

}

当我尝试运行程序时，会出现错误：

线程main中的异常java.lang.ClassCastException任何人都知道有什么问题？/ b>

=h2_lin>解决方案

这是因为库存不实现可比较的。实现它：

  public class库存实现可比较&库存> {
 public int compareTo（Stock o）{
 // ... 
} 
} 
  

...或将 CompareByValue 的实例作为参数传递给 sort（） 方法：

  Collections.sort（list，new CompareByValue（））; 
  

I am doing a java project and I got this problem and don't know how to fix it.

The classes in my project (simplified):

public class Item {

    private String itemID;
    private Integer price;

    public Integer getPrice() {

        return this.price;

    }

}

public class Store {

    private String storeID;
    private String address;

}

public class Stock {

    private Item item;
    private Store store;
    private Integer itemCount;

    public Integer getInventoryValue() {

        return this.item.getPrice() * this.itemCount;

    }  
}

Then I try to sort an ArrayList of Stock so I create another class called CompareByValue

public class CompareByValue implements Comparator<Stock> {

    @Override
    public int compare(Stock stock1, Stock stock2) {

        return (stock1.getInventoryValue() - stock2.getInventoryValue());

    }

}

When I try to run the program, it gives the error:

Exception in thread "main" java.lang.ClassCastException: Stock cannot be cast to java.lang.Comparable

Anyone know what's wrong?

解决方案

It's because Stock isn't implementing Comparable. Either implement it:

public class Stock implements Comparable<Stock> {
    public int compareTo(Stock o) {
        // ...
    }
}

... Or pass an instance of CompareByValue as parameter to the sort() method:

Collections.sort(list, new CompareByValue());

这篇关于MyClass不能转换为java.lang.Comparable：java.lang.ClassCastException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！