用Collections.sort方法对list排序有两种方法
第一种是list中的对象实现Comparable接口，如下：
User.java
1 public class User implements Comparable<User>{ 2 //这个地方的Comparable接口后面一定要跟泛型.否则经常编译错误. 3 private String name; 4 private Integer order; 5 public String getName() { 6 return name; 7 } 8 public void setName(String name) { 9 this.name = name; 10 } 11 public Integer getOrder() { 12 return order; 13 } 14 public void setOrder(Integer order) { 15 this.order = order; 16 } 17 18 public int compareTo(User user) { 19 return this.getOrder().compareTo(user.getOrder()); 20 } 21 }
对应的测试类
Test.java
1 import java.util.ArrayList; 2 import java.util.Collections; 3 import java.util.List; 4 5 public class Test{ 6 public static void main(String[] args) { 7 User user1 = new User(); 8 user1.setName("a"); 9 user1.setOrder(1); 10 User user2 = new User(); 11 user2.setName("b"); 12 user2.setOrder(2); 13 List<User> list = new ArrayList<User>(); 14 //此处add user2再add user1 15 list.add(user2); 16 list.add(user1); 17 Collections.sort(list); 18 for(User u : list){ 19 System.out.println(u.getName()); 20 } 21 } 22 }
输出结果
a
b
第二种方法是根据Collections.sort重载方法来实现，例如：
User.java
1 /** 2 * 根据order对User排序 3 */ 4 public class User { //此处无需实现Comparable接口 5 private String name; 6 private Integer order; 7 public String getName() { 8 return name; 9 } 10 public void setName(String name) { 11 this.name = name; 12 } 13 public Integer getOrder() { 14 return order; 15 } 16 public void setOrder(Integer order) { 17 this.order = order; 18 } 19 }
主类中这样写即可：
Test.java
1 import java.util.ArrayList; 2 import java.util.Collections; 3 import java.util.Comparator; 4 import java.util.List; 5 6 public class Test2{ 7 public static void main(String[] args) { 8 User user1 = new User(); 9 user1.setName("a"); 10 user1.setOrder(1); 11 User user2 = new User(); 12 user2.setName("b"); 13 user2.setOrder(2); 14 List<User> list = new ArrayList<User>(); 15 list.add(user2); 16 list.add(user1); 17 18 Collections.sort(list,new Comparator<User>(){ 19 public int compare(User user1, User user2) { 20 return user1.getOrder().compareTo(user2.getOrder()); 21 } 22 }); 23 for(User u : list){ 24 System.out.println(u.getName()); 25 } 26 } 27 }
输出结果
a
b
前者代码结构简单，但是只能根据固定的属性排序，后者灵活，可以临时指定排序项，但是代码不够简洁
多字段的场合：
Collections.sort(list,new Comparator(){ public int compare(User arg0, User arg1) { // 第一次比较专业 int i = arg0.getOrder().compareTo(arg1.getOrder()); // 如果专业相同则进行第二次比较 if(i==0){ // 第二次比较 int j=arg0.getXXX().compareTo(arg1.getXXX()); // 如果学制相同则返回按年龄排序 if(j==0){ return arg0.getCCC().compareTo(arg1.getCCC()); } return j; } return i; } });
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
例子二:
1 import java.util.ArrayList; 2 import java.util.Collections; 3 import java.util.Comparator; 4 import java.util.List; 5 6 public class CollectionSortTest { 7 public static void main(String[] args) { 8 List<String> lists = new ArrayList<String>(); 9 lists.add("5"); 10 lists.add("2"); 11 lists.add("9"); 12 // lists中的对象String 本身含有compareTo方法，所以可以直接调用sort方法，按自然顺序排序，即升序排序 13 Collections.sort(lists); 14 System.out.println(lists); 15 16 List<A> list = new ArrayList<A>(); 17 A aa = new A(); 18 aa.setName("aa"); 19 aa.setOrder(1); 20 A bb = new A(); 21 bb.setName("bb"); 22 bb.setOrder(2); 23 list.add(bb); 24 list.add(aa); 25 // list中的对象A实现Comparable接口 26 Collections.sort(list); 27 System.out.println(list); 28 29 List<B> listB = new ArrayList<B>(); 30 B ab = new B(); 31 ab.setName("ab"); 32 ab.setOrder("1"); 33 B ba = new B(); 34 ba.setName("ba"); 35 ba.setOrder("2"); 36 listB.add(ba); 37 listB.add(ab); 38 // 根据Collections.sort重载方法来实现 39 Collections.sort(listB, new Comparator<B>() { 40 @Override 41 public int compare(B b1, B b2) { 42 return b1.getOrder().compareTo(b2.getOrder()); 43 } 44 }); 45 46 System.out.println(listB); 47 } 48 } 49 50 class A implements Comparable<A> { 51 private String name; 52 private Integer order; 53 public String getName() { 54 return name; 55 } 56 public void setName(String name) { 57 this.name = name; 58 } 59 public Integer getOrder() { 60 return order; 61 } 62 public void setOrder(Integer order) { 63 this.order = order; 64 } 65 @Override 66 public String toString() { 67 return "name is " + name + " order is " + order; 68 } 69 @Override 70 public int compareTo(A a) { 71 return this.order.compareTo(a.getOrder()); 72 } 73 } 74 class B { 75 private String name; 76 private String order; 77 public String getName() { 78 return name; 79 } 80 public void setName(String name) { 81 this.name = name; 82 } 83 public String getOrder() { 84 return order; 85 } 86 public void setOrder(String order) { 87 this.order = order; 88 } 89 @Override 90 public String toString() { 91 return "name is " + name + " order is " + order; 92 } 93 }
打印结果:
[2, 5, 9] [name is aa order is 1, name is bb order is 2] [name is ab order is 1, name is ba order is 2]
本文转自SummerChill博客园博客，原文链接：http://www.cnblogs.com/DreamDrive/p/4284865.html，如需转载请自行联系原作者
