用Java集合中的Collections.sort方法对list排序的两种方法
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第一种是list中的对象实现Comparable接口,如下:
/*** 根据order对User排序*/public class User implements Comparable<USER> { private String name; private Integer order; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getOrder() { return order; } public void setOrder(Integer order) { this.order = order; } public int compareTo(User arg0) { return this.getOrder().compareTo(arg0.getOrder()); }} 测试一下:
public class Test{ public static void main(String[] args) { User user1 = new User(); user1.setName("a"); user1.setOrder(1); User user2 = new User(); user2.setName("b"); user2.setOrder(2); List <USER> list = new ArrayList <USER> (); //此处add user2再add user1 list.add(user2); list.add(user1); Collections.sort(list); for(User u : list){ System.out.println(u.getName()); } }}
第二种方法是根据Collections.sort重载方法来实现,例如:
/*** 根据order对User排序*/public class User { //此处无需实现Comparable接口 private String name; private Integer order; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getOrder() { return order; } public void setOrder(Integer order) { this.order = order; }}
主类中这样写即可:
public class Test{ public static void main(String[] args) { User user1 = new User(); user1.setName("a"); user1.setOrder(1); User user2 = new User(); user2.setName("b"); user2.setOrder(2); List<USER> list = new ArrayList <USER> (); list.add(user2); list.add(user1); Collections.sort(list,new Comparator <USER>(){ public int compare(User arg0, User arg1) { return arg0.getOrder().compareTo(arg1.getOrder()); } }); for(User u : list){ System.out.println(u.getName()); } }}输出结果如下 ab 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 <USER> (){ 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; } });