question_013-JAVA之Set之TreeSet

question_013-JAVA之Set之TreeSet

TreeSet

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TreeSet【唯一性和排序性】

强制对加入的元素进行排序【排序的方法：自然排序和比较器排序】

·········默认是自然排序，对于【基础类型，会默认自然排序】

·········实现Comparable<T>接口的compare()方法，比较器排序【自定义类型一般要自己使用比较器排序】

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1）
使用元素的自然顺序对元素进行排序

2）
或者根据创建 set 时提供的 Comparator进行排序具体取决于使用的构造方法。

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对于自定义对象的排序方式1

package com.lyTs;

/**

* 如果一个类的元素要实现自然排序，必须实现自然排序接口

*

* @author Jack

*

*/

public class Student implements Comparable<Student> {

private String name;

private int age;

public Student() {

}

public Student(String name, int age) {

this.name = name;

this.age = age;

}

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;

}

// 实现比较接口，自己定义比较器

@Override

public int compareTo(Student o) {

// return -1;

// 名称相同吗，不同则加入

// 名称相同，则比较name

int num = (this.age - o.age);
int num2 = num == 0 ? this.name.compareTo(o.name): num;

return num2;

}

}

·············································
package com.lyTs;

import java.util.TreeSet;

public class TreeSetDemo {

public static void main(String[] args) {

TreeSet<Student> ts = new TreeSet<Student>();

Student s1 = new Student("zhangsan",18);

Student s2 = new Student("lisi",21);

Student s3 = new Student("wangwu",33);

Student s4 = new Student("zhaoliu",45);

Student s5 = new Student("fengqi",6);

Student s6 = new Student("wangba.",33);

ts.add(s1);

ts.add(s2);

ts.add(s3);

ts.add(s4);

ts.add(s5);

ts.add(s6);

for(Student i : ts){

System.out.println(i.getName()+"----"+ i.getAge());

}

}

}

·····················结果···················

fengqi----6

zhangsan----18

lisi----21

wangba.----33

wangwu----33

zhaoliu----45

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对于自定义对象的排序方式2

·······学生类中没有比较方法···············

package com.lyTsComparator;

/**

* @author Jack

*/

public class Student{

private String name;

private int age;

public Student() {

}

public Student(String name, int age) {

this.name = name;

this.age = age;

}

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;

}

}

···············比较器··················
package com.lyTsComparator;

import java.util.Comparator;

public class MyComparator implements Comparator<Student> {

@Override

public int compare(Student o1, Student o2) {

// 姓名的长度相同

int num = o1.getName().length() - o2.getName().length();

// 姓名的长度相同，不代表内容相同

int num2 = num == 0? o1.getName().compareTo(o2.getName()):num;

int num3 = num2 == 0?o1.getAge() - o2.getAge():num2;

return num3;

}

}

···············测试··················

package com.lyTsComparator;

import java.util.TreeSet;

public class TreeSetDemo {

public static void main(String[] args) {

TreeSet<Student> ts = new TreeSet<Student>(new MyComparator());

Student s1 = new Student("zhangsan",18);

Student s2 = new Student("lisi",21);

Student s3 = new Student("wangwu",33);

Student s4 = new Student("zhaoliu",45);

Student s5 = new Student("fengqi",6);

Student s7 = new Student("fengqi",33);

Student s6 = new Student("wangba.",33);

ts.add(s1);

ts.add(s2);

ts.add(s3);

ts.add(s4);

ts.add(s5);

ts.add(s6);

for(Student i : ts){

System.out.println(i.getName()+"----"+ i.getAge());

}

}

}

```````````````j结果```````````````
lisi----21

fengqi----6

wangwu----33

wangba.----33

zhaoliu----45

zhangsan----18

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对于自定义对象的排序方式3

·······学生类中没有比较方法···············

package com.lyTsComparator;

/**

* @author Jack

*/

public class Student{

private String name;

private int age;

public Student() {

}

public Student(String name, int age) {

this.name = name;

this.age = age;

}

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;

}

}

···············测试··················

使用了匿名比较器

package com.lyTsComparator;

import java.util.TreeSet;

public class TreeSetDemo {

public static void main(String[] args) {

TreeSet<Student> ts = new TreeSet<Student>(new MyComparator());

// 使用匿名内部类，来实现

TreeSet<Student> ts = new TreeSet<Student>(new Comparator<Student>() {

@Override

public int compare(Student o1, Student o2) {

// 姓名的长度相同

int num = o1.getName().length() - o2.getName().length();

// 姓名的长度相同，不代表内容相同

int num2 = num == 0? o1.getName().compareTo(o2.getName()):num;

int num3 = num2 == 0?o1.getAge() - o2.getAge():num2;

return num3;

}

});

Student s1 = new Student("zhangsan",18);

Student s2 = new Student("lisi",21);

Student s3 = new Student("wangwu",33);

Student s4 = new Student("zhaoliu",45);

Student s5 = new Student("fengqi",6);

Student s7 = new Student("fengqi",33);

Student s6 = new Student("wangba.",33);

ts.add(s1);

ts.add(s2);

ts.add(s3);

ts.add(s4);

ts.add(s5);

ts.add(s6);

for(Student i : ts){

System.out.println(i.getName()+"----"+ i.getAge());

}

}

}

```````````````j结果```````````````
lisi----21

fengqi----6

wangwu----33

wangba.----33

zhaoliu----45

zhangsan----18

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