平等对象比较：JAVA [英] Object comparison for equality : JAVA

问题描述

public ClassA
{
private String firstId;
private String secondId;

public void setFirstId(String firstId) {
           this.firstId = firstId;
   }


   public String getFirstId() {
           return id;
   }

   public void setSecondId(String secondId) {
           this.secondId = secondId;
   }


   public String getSecondId() {
           return secondId;
   }
}



public ClassB
{
private String firstId;
private String secondId;


   public void setFirstId(String firstId) {
           this.firstId = firstId;
   }


   public String getFirstId() {
           return id;
   }

   public void setSecondId(String secondId) {
           this.secondId = secondId;
   }

   public String getSecondId() {
           return secondId;
   }
}

我有以上2个类绝对相同（除了名称当然），我添加到两个数组列表：aListA和aListB。我需要比较两个对象是否相同。如果他们是相同的，我需要将它们添加到另一个列表（commonList），如果他们碰巧是不同的，我需要将它们添加到另一个列表（不同的列表）。我写了以下代码：

I have the above 2 classes(POJOs) which are absolutely the same (except for the name of course) which I am adding to two arraylists: aListA and aListB. I need to compare if the two objects are the same. If they are same I need to add them to another list(commonList) and if they happen to be the different, I need to add them to another list(differentList). I have written the following code:

ClassA clsA = null;
public ArrayList genCommonList(aList, bList)
{

for(int i = 1; i<aList.size(); i++)
{
clsA = new ClassA;
Object obj = aList.get(i);
clsA = (ClassA)obj;
if(bList.contains(clsA)
{
genCommonList.add(clsA);
}
}

public ArrayList genDifferentList(aList, bList)
{

for(int i = 1; i<aList.size(); i++)
{
clsA = new ClassA;
Object obj = aList.get(i);
clsA = (ClassA)obj;
if(!bList.contains(clsA)
{
 genDifferentList.add(clsA);
}
}

我的问题是，即使数据两个变量，firstId和secondID）在两个不同的POJO是相同的，他们被放在不同的列表。这意味着对象不是使用containsList（）方法的ArrayList类进行比较我不想得到是否有一种方法可以比较两个变量的POJO，并确定为等于或不等于？

My problem is that even when the data(both variables, firstId and secondID) in the 2 different POJOs are the same, they get put in the different list. That means the objects are not being compared for equality using the contains() method of the ArrayList class. I dont want to get the data from each variable inside the POJO and compare. Is there a way to compare the POJOs for both variables and be determined as either equal or unequal?

推荐答案

事件内容是相同的，它们是不同的对象，不satifsy等条件。你可能需要做显式的a.getfirstId（）。equals（b.getfirsId（））和a.getscondID （b.getSecondId（））。

Eventhough content is same they are different objects which doesn't satifsy equal condition. You may need to do explicit a.getfirstId().equals(b.getfirsId()) and a.getscondID().equals(b.getSecondId()) by iterating.

另一种可能性是在两个POJO类中覆盖equals和hashcode方法。请参阅此链接，了解 equals / hashcode合同。

The other possibility may be overriding equals and hashcode methods in both POJO classes. Refer this link for equals/hashcode contract.

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