List对象去重和按照某个字段排序的实现方法

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; 
  } 
 
} 

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); 
    } 
  } 

public class mycomparator implements comparator<people> { 
 
  @override 
  public int compare(people p1, people p2) { 
    return p1.getcreatedate().compareto(p2.getcreatedate()); 
  } 
 
} 

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()); 
    } 
  }