有序集合TreeSet
TreeSet<这里的类型要实现compatable接口>
模型里要实现方法compareTo（）；
如果
方法返回0，则只打印第一个
代码：
Student.java
package day20200819;
public class Student implements Comparable<Student>{
int id;
String name;
public Student(int id, String name) {
super();
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + "]";
}
@Override
public int compareTo(Student o) {
// TODO Auto-generated method stub
return 0;
}
}
Demo.java
package day20200819;
import java.util.Set;
import java.util.TreeSet;
public class Demo03 {
public static void main(String[] args) {
//TreeSet
TreeSet<String> set1 = new TreeSet<String>();
set1.add("apple");
set1.add("banana");
set1.add("orange");
System.out.println(set1);
TreeSet<Student> set2 = new TreeSet<Student>();
set2.add(new Student(1, "zhangsan"));
set2.add(new Student(2, "lisi"));
set2.add(new Student(3, "wangwu"));
System.out.println(set2);
}
}
控制台输出：
[apple, banana, orange]
[Student [id=1, name=zhangsan]]
方法返回1，则正序打印所有，
Student.java
package day20200819;
public class Student implements Comparable<Student>{
int id;
String name;
public Student(int id, String name) {
super();
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + "]";
}
@Override
public int compareTo(Student o) {
// TODO Auto-generated method stub
return 1;
}
}
控制台打印：
[apple, banana, orange]
[Student [id=1, name=zhangsan], Student [id=2, name=lisi], Student [id=3, name=wangwu]]
方法返回-1，则倒序打印，
Student.java
package day20200819;
public class Student implements Comparable<Student>{
int id;
String name;
public Student(int id, String name) {
super();
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + "]";
}
@Override
public int compareTo(Student o) {
// TODO Auto-generated method stub
return -1;
}
}
控制台打印：
[apple, banana, orange]
[Student [id=3, name=wangwu], Student [id=2, name=lisi], Student [id=1, name=zhangsan]]