List对象去重和按照某个字段排序的实现方法
程序员文章站
2024-02-17 14:34:34
1、list
1、list<object>去重
people类
public class people { private int id; private string name; private date createdate; public int getid() { return id; } public void setid(int id) { this.id = id; } public string getname() { return name; } public void setname(string name) { this.name = name; } public date getcreatedate() { return createdate; } public void setcreatedate(date createdate) { this.createdate = createdate; } }
main方法
public static void main(string[] args) throws exception{ list<people> list = new arraylist<people>(); people p1 = new people(); p1.setid(1); p1.setname("赵"); list.add(p1); people p2 = new people(); p2.setid(2); p2.setname("钱"); list.add(p2); people p3 = new people(); p3.setid(3); p3.setname("孙"); list.add(p3); people p4 = new people(); p4.setid(4); p4.setname("李"); list.add(p4); people p5 = new people(); p5.setid(5); p5.setname("周"); list.add(p5); list.add(p1); for(people p : list){ system.out.println(p); } system.out.println("=========================="); set<people> set = new hashset<people>(list); list.clear(); list.addall(new arraylist<people>(set)); for(people p : list){ system.out.println(p); } }
2、list<object>按照日期字段排序
自定义comparator
public class mycomparator implements comparator<people> { @override public int compare(people p1, people p2) { return p1.getcreatedate().compareto(p2.getcreatedate()); } }
main方法
public static void main(string[] args) throws exception{ list<people> list = new arraylist<people>(); people p1 = new people(); p1.setid(1); p1.setname("赵"); p1.setcreatedate(new date(new date().gettime() + 1000)); list.add(p1); people p2 = new people(); p2.setid(2); p2.setname("钱"); p2.setcreatedate(new date(new date().gettime() + 8000)); list.add(p2); people p3 = new people(); p3.setid(3); p3.setname("孙"); p3.setcreatedate(new date(new date().gettime() + 7000)); list.add(p3); people p4 = new people(); p4.setid(4); p4.setname("李"); p4.setcreatedate(new date(new date().gettime() + 5000)); list.add(p4); people p5 = new people(); p5.setid(5); p5.setname("周"); p5.setcreatedate(new date(new date().gettime() + 6000)); list.add(p5); for(people p : list){ system.out.println(p.getid()); } //1,2,3,4,5 system.out.println("======================="); collections.sort(list, new mycomparator()); //1,4,5,3,2 for(people p : list){ system.out.println(p.getid()); } }
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