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()); 
    } 
  }