List<对象>去重
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package ss;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
public class HashCodeTest {
public static class AlarmInfoDTO {
private String alarmsType;
private String timestamp;
private String numberPlate;
public AlarmInfoDTO(String alarmsType,String timestamp,String numberPlate) {
// TODO Auto-generated constructor stub
this.alarmsType = alarmsType;
this.numberPlate = numberPlate;
this.timestamp = timestamp;
}
@Override
public boolean equals(Object obj) {
if(this==obj){
return true ;
}
if(!(obj instanceof AlarmInfoDTO)){
return false ;
}
AlarmInfoDTO alarmInfo = (AlarmInfoDTO)obj ; // 向下转型
return this.alarmsType.equals(alarmInfo.alarmsType)&&
this.timestamp.equals(alarmInfo.timestamp)&&
this.numberPlate.equals(alarmInfo.numberPlate);//&&
}
@Override
public int hashCode() {
// TODO Auto-generated method stub
return this.numberPlate.hashCode()*Integer.parseInt(this.alarmsType);
}
private void print(){
System.out.println(this.alarmsType+","+this.numberPlate+","+this.timestamp);
}
}
public static void main(String[] args){
List<AlarmInfoDTO> rs = new ArrayList<HashCodeTest.AlarmInfoDTO>();
rs.add(new AlarmInfoDTO("1","2","20130303"));
rs.add(new AlarmInfoDTO("1","2","20130303"));
rs.add(new AlarmInfoDTO("2","2","20130303"));
rs.add(new AlarmInfoDTO("2","2","20130303"));
rs.add(new AlarmInfoDTO("3","3","20120202"));
rs.add(new AlarmInfoDTO("3","3","20120202"));
rs.add(new AlarmInfoDTO("3","3","20120202"));
rs.add(new AlarmInfoDTO("1","3","20120202"));
rs.add(new AlarmInfoDTO("4","4","20120202"));
HashSet<AlarmInfoDTO> set = new HashSet<AlarmInfoDTO>();
for (int i = 0; i < rs.size(); i++) {
set.add(rs.get(i));
}
List<AlarmInfoDTO> result = new ArrayList<HashCodeTest.AlarmInfoDTO>();
result.addAll(set);
for (int i = 0; i < result.size(); i++) {
result.get(i).print();
}
}
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
public class HashCodeTest {
public static class AlarmInfoDTO {
private String alarmsType;
private String timestamp;
private String numberPlate;
public AlarmInfoDTO(String alarmsType,String timestamp,String numberPlate) {
// TODO Auto-generated constructor stub
this.alarmsType = alarmsType;
this.numberPlate = numberPlate;
this.timestamp = timestamp;
}
@Override
public boolean equals(Object obj) {
if(this==obj){
return true ;
}
if(!(obj instanceof AlarmInfoDTO)){
return false ;
}
AlarmInfoDTO alarmInfo = (AlarmInfoDTO)obj ; // 向下转型
return this.alarmsType.equals(alarmInfo.alarmsType)&&
this.timestamp.equals(alarmInfo.timestamp)&&
this.numberPlate.equals(alarmInfo.numberPlate);//&&
}
@Override
public int hashCode() {
// TODO Auto-generated method stub
return this.numberPlate.hashCode()*Integer.parseInt(this.alarmsType);
}
private void print(){
System.out.println(this.alarmsType+","+this.numberPlate+","+this.timestamp);
}
}
public static void main(String[] args){
List<AlarmInfoDTO> rs = new ArrayList<HashCodeTest.AlarmInfoDTO>();
rs.add(new AlarmInfoDTO("1","2","20130303"));
rs.add(new AlarmInfoDTO("1","2","20130303"));
rs.add(new AlarmInfoDTO("2","2","20130303"));
rs.add(new AlarmInfoDTO("2","2","20130303"));
rs.add(new AlarmInfoDTO("3","3","20120202"));
rs.add(new AlarmInfoDTO("3","3","20120202"));
rs.add(new AlarmInfoDTO("3","3","20120202"));
rs.add(new AlarmInfoDTO("1","3","20120202"));
rs.add(new AlarmInfoDTO("4","4","20120202"));
HashSet<AlarmInfoDTO> set = new HashSet<AlarmInfoDTO>();
for (int i = 0; i < rs.size(); i++) {
set.add(rs.get(i));
}
List<AlarmInfoDTO> result = new ArrayList<HashCodeTest.AlarmInfoDTO>();
result.addAll(set);
for (int i = 0; i < result.size(); i++) {
result.get(i).print();
}
}
}
对于List对象存储去重最重要的就是要重写equals和hashCode这两个方法,缺一不可。
转自:http://blog.csdn.net/kaypro/article/details/10145991
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