TreeSet排序

TreeSet的排序能够通过两种方法来实现：

1.通过TreeSet(Comparator<?
super E> comparator) 构造方法指定TreeSet的比較器进行排序。

2.使用TreeSet()构造方法。并对须要加入到set集合中的元素实现Comparable接口进行排序；

方法一样例：

person类：

public class Person {
private String name;
private int age;
private String date;

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getDate() {
return date;
}
public void setDate(String date) {
this.date = date;
}
public Person(String name) {
this.name=name;
}
public Person() {
}

@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + ", date=" + date + "]";
}
public Person(String name, int age, String date) {
super();
this.name = name;
this.age = age;
this.date = date;
}

}

自己实现比較器：

import java.util.Comparator;
public class MyComparator implements Comparator<Person>{
@Override
public int compare(Person p1, Person p2) {
if(p1.getAge()>p2.getAge()){
return 1;
}else if(p1.getAge()==p2.getAge()){
return 0;
}else{
return -1;
}
}

}

測试数据：

@Test
public void treeSet(){//全部元素总是依据指定排序规则保持有序状态。

Set<Person> set = new TreeSet<Person>(new MyComparator());
set.add(new Person("aaa", 67, "254"));
set.add(new Person("bbb", 16, "254"));
set.add(new Person("ccc", 1, "254"));
set.add(new Person("ddd", 675, "254"));
System.out.println(set);
}

结果：


方法二样例：

person类，须要实现Comparable接口，并重写compareTo()方法。compareTo方法中定义排序的方式

public class Person2 implements Comparable {
private String name;
private int age;
private String date;

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public String getDate() {
return date;
}

public void setDate(String date) {
this.date = date;
}

public Person2(String name) {
this.name = name;
}

public Person2() {
}

@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + ", date=" + date + "]";
}

public Person2(String name, int age, String date) {
super();
this.name = name;
this.age = age;
this.date = date;
}

@Override
public int compareTo(Object obj) {
if (obj instanceof Person2) {//instanceof推断内存中实际对象obj是不是Person2类型
Person2 p = (Person2) obj;
if (this.age > p.getAge()) {
return 1;
} else if (this.age == p.getAge()) {
return 0;
} else {
return -1;
}
}
return 0;
}

}

測试数据：

@Test
public void treeSet2(){
Set<Person2> set = new TreeSet<Person2>();
set.add(new Person2("aaa", 67, "254"));
set.add(new Person2("bbb", 16, "254"));
set.add(new Person2("ccc", 1, "254"));
set.add(new Person2("ddd", 675, "254"));
System.out.println(set);
}

測试结果：

[Person [name=ccc, age=10, date=254], Person [name=eee, age=12, date=254], Person [name=bbb, age=16, date=254], Person [name=aaa, age=67,
date=254], Person [name=ddd, age=675, date=254]]