List对象去重和按照某个字段排序的实现方法

List对象去重和按照某个字段排序的实现方法

1、List

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 list = new ArrayList();

People p1 = new PeoEeDJtVBuple();

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 set = new HashSet(list);

list.clear();

list.addAll(new ArrayList(set));

for(People p : list){

System.out.println(p);

}

}

2、List

自定义Comparator

public class MyComparator implements Comparator {

@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 list = new ArrayList();

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.seEeDJtVButName("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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