在前端和后端交互的过程中,对于列表类的数据,有时候服务器发来的数据是重复的,这种列表类的数据大多和单元Bean类有联系,而且每个Bean一般都有id,所以,我们可以根据id来进行判断去重,然而怎么根据id来去重呢?这就需要我们重写Bean的equals和hashCode方法来比较了,上代码吧: 首先我们定义一个User的Bean类:

public class User extends Bean{    public String id;    public String name;    public int age;    //去重关键,重写equals方法    @Override    public boolean equals(Object o) {        User user = (User) o;        return user.id.equals(id);    }    //去重关键,把User的id当做对象的哈希表值返回    @Override    public int hashCode() {        return id.hashCode();    }    }

测试代码:

import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.util.Log;import com.example.administrator.test.R;import com.example.administrator.test.bean.User;import java.util.ArrayList;import java.util.HashSet;import java.util.Iterator;import java.util.List;import java.util.Set;public class RemoveDepulicateDataActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_remove_depulicate_data);        User user1 = new User();        user1.id = "12";        user1.name = "aaa";        user1.age = 10;        User user2 = new User();        user2.id = "13";        user2.name = "aaa";        user2.age = 11;        User user3 = new User();        user3.id = "14";        user3.name = "aaa";        user3.age = 11;        User user4 = new User();        user4.id = "15";        user4.name = "aaa";        user4.age = 11;        User user5 = new User();        user5.id = "15";        user5.name = "aaa";        user5.age = 11;        List
    
      list = new ArrayList<>();        list.add(user1);        list.add(user2);        list.add(user3);        list.add(user4);        list.add(user5);        remove(list);        Log.e("after del depulicate",list.size()+"");    }    //去Bean类重    public void remove(List
     
       list){        Log.e("before del depulicate",list.size()+"");        Set
      
        set = new HashSet<>();        List
       
         listaaa = new ArrayList<>();        for (Iterator
        
          ite = list.iterator();ite.hasNext();){            User aaa = ite.next();            if (set.add(aaa)){                listaaa.add(aaa);            }        }        list.clear();        list.addAll(listaaa);    }}
        
       
      
     
    

通过以上代码我们可以知道,HashSet的判重是根据元素的hashCode方法和equals方法共同决定的.送大家一片文章来温习下,hashCode和equals的原理.

新增

另一种的去重方式:```public void removeDepulicate(List list) {    for  ( int  i  =   0 ; i  <  list.size()  -   1 ; i ++ )   {        for  ( int  j  =  list.size()  -   1 ; j  >  i; j -- )   {            if  (((DialogueBean) list.get(j)).getId().equals(((DialogueBean) list.get(i)).getId()))   {                list.remove(j);            }        }    }}```