TreeSet、Comparable、Comparator、内部类、匿名类

1 package com.tn.treeSet;
2
3 public class Student {
4     private String name;
5     private int age;
6     public Student(){}
7     public Student(String name, int age) {
8         super();
9         this.name = name;
10         this.age = age;
11     }
12     public String getName() {
13         return name;
14     }
15     public void setName(String name) {
16         this.name = name;
17     }
18     public int getAge() {
19         return age;
20     }
21     public void setAge(int age) {
22         this.age = age;
23     }
24     @Override
25     public String toString() {
26         return "Student [name=" + name + "]";
27     }
28 }



 1 package com.tn.treeSet;
2
3 import java.util.TreeSet;
4
5 public class TreeSetDemo {
6     public static void main(String[] args){
7         TreeSet<Student> students=new TreeSet<>();//后一个尖括号内可以省略类型
8         Student student1=new Student("武松",30);
9         Student student2=new Student("林冲",31);
10         Student student3=new Student("鲁智深",29);
11         students.add(student1);
12         students.add(student2);
13         students.add(student3);
14         System.out.println(students);
15     }
16 }


 运行结果：



原因:TreeSet中加入的对象需要能进行比较，即实现Comparable接口

 改造一：在Student类中实现Comparable接口



1 package com.tn.treeSet;
2
3 public class Student implements Comparable<Student> {
4     private String name;
5     private int age;
6     public Student(){}
7     public Student(String name, int age) {
8         super();
9         this.name = name;
10         this.age = age;
11     }
12     public String getName() {
13         return name;
14     }
15     public void setName(String name) {
16         this.name = name;
17     }
18     public int getAge() {
19         return age;
20     }
21     public void setAge(int age) {
22         this.age = age;
23     }
24     @Override
25     public String toString() {
26         return "Student [name=" + name + "]";
27     }
28     @Override
29     public int compareTo(Student o) {
30         if(!this.equals(o)){
31 //            return this.name.compareTo(o.name);
32             return o.name.compareTo(this.name);//和上面语句打印顺序颠倒。
33         }
34         return 0;
35     }
36 }




1 package com.tn.treeSet;
2
3 import java.util.TreeSet;
4
5 public class TreeSetDemo {
6     public static void main(String[] args){
7         TreeSet<Student> students=new TreeSet<>();//后一个尖括号内可以省略类型
8         Student student1=new Student("武松",30);
9         Student student2=new Student("林冲",31);
10         Student student3=new Student("鲁智深",29);
11         students.add(student1);
12         students.add(student2);
13         students.add(student3);
14         System.out.println(students);
15     };//方法体结结尾大括号后有;不会报错
16 };//类体最后一个大括号后有;不会报错


改造二：用内部类实现Comparator接口



1 package com.tn.treeSet;
2
3 public class Student{
4     private String name;
5     private int age;
6     public Student(){}
7     public Student(String name, int age) {
8         super();
9         this.name = name;
10         this.age = age;
11     }
12     public String getName() {
13         return name;
14     }
15     public void setName(String name) {
16         this.name = name;
17     }
18     public int getAge() {
19         return age;
20     }
21     public void setAge(int age) {
22         this.age = age;
23     }
24     @Override
25     public String toString() {
26         return "Student [name=" + name + "]";
27     }
28 }




1 package com.tn.treeSet;
2
3 import java.util.Comparator;
4 import java.util.TreeSet;
5
6 public class TreeSetDemo {
7     public static void main(String[] args){
8         Student student1=new Student("武松",30);
9         Student student2=new Student("林冲",31);
10         Student student3=new Student("鲁智深",29);
11         //TreeSet构造时用Comparator作为构造函数参数
12         TreeSet<Student> students=new TreeSet<Student>(new ComparatorDemo());
13         students.add(student1);
14         students.add(student2);
15         students.add(student3);
16         System.out.println(students);
17     }
18     static class ComparatorDemo implements Comparator<Student>{
19 //        内部类要写在类体里，但不能写进类中方法体内。
20         @Override
21         public int compare(Student o1, Student o2) {
22             return o1.getName().compareTo(o2.getName());
23         }
24     }
25 }


 改造三：用匿名类实现Comparator接口



1 package com.tn.treeSet;
2
3 public class Student{
4     private String name;
5     private int age;
6     public Student(){}
7     public Student(String name, int age) {
8         super();
9         this.name = name;
10         this.age = age;
11     }
12     public String getName() {
13         return name;
14     }
15     public void setName(String name) {
16         this.name = name;
17     }
18     public int getAge() {
19         return age;
20     }
21     public void setAge(int age) {
22         this.age = age;
23     }
24     @Override
25     public String toString() {
26         return "Student [name=" + name + "]";
27     }
28 }




1 package com.tn.treeSet;
2
3 import java.util.Comparator;
4 import java.util.TreeSet;
5
6 public class TreeSetDemo {
7     public static void main(String[] args) {
8         Student student1 = new Student("武松", 30);
9         Student student2 = new Student("林冲", 31);
10         Student student3 = new Student("鲁智深", 29);
11
12         TreeSet<Student> students = new TreeSet<Student>(
13                 new Comparator<Student>() {
14                     @Override
15                     public int compare(Student o1, Student o2) {
16                         return o1.getName().compareTo(o2.getName());
17                     }
18                 });
19         students.add(student1);
20         students.add(student2);
21         students.add(student3);
22         System.out.println(students);
23     }
24 }


 总结：

TreeSet容器中的对象要能排序，两种实现排序方法：

1.TreeSet使用无参构造函数，容器中的对象实现Comparable接口，见改造一；

2.TreeSet构造时使用Comparator作为构造函数参数；

　　比较方法如果返回0，则对象不能重复加入。

TreeSet底层是TreeMap

转载自：http://www.cnblogs.com/xiongjiawei/p/6623063.html