【java】TreeSet、Comparable、Comparator、内部类、匿名类

 package com.tn.treeSet;

 public class Student {
     private String name;
     private int age;
     public Student(){}
     public Student(String name, int age) {
         super();
         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;
     }
     @Override
     public String toString() {
         return "Student [name=" + name + "]";
     }
 }

Student

 package com.tn.treeSet;

 import java.util.TreeSet;

 public class TreeSetDemo {
     public static void main(String[] args){
         TreeSet<Student> students=new TreeSet<>();//后一个尖括号内可以省略类型
         Student student1=new Student("武松",30);
         Student student2=new Student("林冲",31);
         Student student3=new Student("鲁智深",29);
         students.add(student1);
         students.add(student2);
         students.add(student3);
         System.out.println(students);
     }
 }

TreeSetDemo

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

 package com.tn.treeSet;

 public class Student implements Comparable<Student> {
     private String name;
     private int age;
     public Student(){}
     public Student(String name, int age) {
         super();
         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;
     }
     @Override
     public String toString() {
         return "Student [name=" + name + "]";
     }
     @Override
     public int compareTo(Student o) {
         if(!this.equals(o)){
 //            return this.name.compareTo(o.name);
             return o.name.compareTo(this.name);//和上面语句打印顺序颠倒。
         }
         return 0;
     }
 }

Student

 package com.tn.treeSet;

 import java.util.TreeSet;

 public class TreeSetDemo {
     public static void main(String[] args){
         TreeSet<Student> students=new TreeSet<>();//后一个尖括号内可以省略类型
         Student student1=new Student("武松",30);
         Student student2=new Student("林冲",31);
         Student student3=new Student("鲁智深",29);
         students.add(student1);
         students.add(student2);
         students.add(student3);
         System.out.println(students);
     };//方法体结结尾大括号后有;不会报错
 };//类体最后一个大括号后有;不会报错

TreeSetDemo

---

改造二：用内部类实现Comparator接口

 package com.tn.treeSet;

 public class Student{
     private String name;
     private int age;
     public Student(){}
     public Student(String name, int age) {
         super();
         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;
     }
     @Override
     public String toString() {
         return "Student [name=" + name + "]";
     }
 }

Student

 package com.tn.treeSet;

 import java.util.Comparator;
 import java.util.TreeSet;

 public class TreeSetDemo {
     public static void main(String[] args){
         Student student1=new Student("武松",30);
         Student student2=new Student("林冲",31);
         Student student3=new Student("鲁智深",29);
         //TreeSet构造时用Comparator作为构造函数参数
         TreeSet<Student> students=new TreeSet<Student>(new ComparatorDemo());
         students.add(student1);
         students.add(student2);
         students.add(student3);
         System.out.println(students);
     }
     static class ComparatorDemo implements Comparator<Student>{
 //        内部类要写在类体里，但不能写进类中方法体内。
         @Override
         public int compare(Student o1, Student o2) {
             return o1.getName().compareTo(o2.getName());
         }
     }
 }

TreeSetDemo

---

改造三：用匿名类实现Comparator接口

 package com.tn.treeSet;

 public class Student{
     private String name;
     private int age;
     public Student(){}
     public Student(String name, int age) {
         super();
         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;
     }
     @Override
     public String toString() {
         return "Student [name=" + name + "]";
     }
 }

Student

 package com.tn.treeSet;

 import java.util.Comparator;
 import java.util.TreeSet;

 public class TreeSetDemo {
     public static void main(String[] args) {
         Student student1 = new Student("武松", 30);
         Student student2 = new Student("林冲", 31);
         Student student3 = new Student("鲁智深", 29);

         TreeSet<Student> students = new TreeSet<Student>(
                 new Comparator<Student>() {
                     @Override
                     public int compare(Student o1, Student o2) {
                         return o1.getName().compareTo(o2.getName());
                     }
                 });
         students.add(student1);
         students.add(student2);
         students.add(student3);
         System.out.println(students);
     }
 }

TreeSetDemo

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