java List对象排序
java List 排序 Collections.sort() 对 List 排序
1 //一个POJO例子 2 3 class User { 4 String name; 5 String age; 6 7 public User(String name,String age){ 8 this.name=name; 9 this.age=age; 10 } 11 public String getAge() { 12 return age; 13 } 14 public void setAge(String age) { 15 this.age = age; 16 } 17 public String getName() { 18 return name; 19 } 20 public void setName(String name) { 21 this.name = name; 22 } 23 } 24 25 26 //具体的比较类，实现Comparator接口 27 28 import java.util.Comparator; 29 import java.util.List; 30 import java.util.ArrayList; 31 import java.util.Collections; 32 33 public class ComparatorUser implements Comparator{ 34 35 public int compare(Object arg0, Object arg1) { 36 User user0=(User)arg0; 37 User user1=(User)arg1; 38 39 //首先比较年龄，如果年龄相同，则比较名字 40 41 int flag=user0.getAge().compareTo(user1.getAge()); 42 if(flag==0){ 43 return user0.getName().compareTo(user1.getName()); 44 }else{ 45 return flag; 46 } 47 } 48 49 } 50 51 52 53 54 //测试类 55 public class SortTest { 56 57 58 public static void main(String[] args){ 59 List userlist=new ArrayList(); 60 userlist.add(new User("dd","4")); 61 userlist.add(new User("aa","1")); 62 userlist.add(new User("ee","5")); 63 userlist.add(new User("bb","2")); 64 userlist.add(new User("ff","5")); 65 userlist.add(new User("cc","3")); 66 userlist.add(new User("gg","6")); 67 68 ComparatorUser comparator=new ComparatorUser(); 69 Collections.sort(userlist, comparator); 70 71 for (int i=0;i<userlist.size();i++){ 72 User user_temp=(User)userlist.get(i); 73 System.out.println(user_temp.getAge()+","+user_temp.getName()); 74 } 75 76 } 77 } 78 79 //首先年龄排序，如果年龄相同，则按名字排序 80 81 结果: 82 1, aa 83 2, bb 84 3, cc 85 4, dd 86 5, ee //注意:同样是5岁的人，则比较名字(ee,ff)，然后排序 87 5, ff 88 6, gg
再举一个例子：
1.现有对象
1 List<Map<String, Object>> loanPayList= new ArrayList<Map<String, Object>>(loanPayList.size());
2.实现Comparator接口
1 class LoanPayComparator implements Comparator<Object>{ 2 @SuppressWarnings("unchecked") 3 public int compare(Object obj1, Object obj2) { 4 Date d1 = (Date) ((Map<String, ?>) obj1).get(OTS_LOAN_PAY_BY_DATE); 5 Date d2 = (Date) ((Map<String, ?>) obj2).get(OTS_LOAN_PAY_BY_DATE); 6 if (d1 == null || d2 == null) { 7 LOG.warn("[loanPayComparator:compare()] sorted date is null."); 8 return 0; 9 } else { 10 if ((d1.getTime()) < d2.getTime()) { 11 return 1; 12 } else if ((d1.getTime()) > d2.getTime()) { 13 return -1; 14 } else { 15 return 0; 16 } 17 } 18 } 19 }
3.排序
1 Collections.sort(loanPayList, new LoanPayComparator());
