TreeSet排序

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TreeSet的排序可以通过两种方法来实现：

1.通过TreeSet(Comparator<? super E> comparator) 构造方法指定TreeSet的比较器进行排序；

2.使用TreeSet()构造方法，并对需要添加到set集合中的元素实现Comparable接口进行排序；

方法一例子：

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() {}@Overridepublic 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;}}

自己实现比较器：

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

测试数据：

@Testpublic void treeSet(){//所有元素总是根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：

方法二例子：

person类，需要实现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() {}@Overridepublic 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;}@Overridepublic int compareTo(Object obj) {if (obj instanceof Person2) {//instanceof判断内存中实际对象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;}}

测试数据：

@Testpublic 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); }

测试结果：

[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]]

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