java-排序，TreeSet

• TreeSet集合概述

  • 元素有序，可以按照一定的规则进行排序，具体排序方式取决于构造方法
    • TreeSet()：根据其元素的自然排序进行排序, 无参构造构造方法若排序的是对象，则对象实现Comparable接口，重写compareTo(T o)方法
    • TreeSet(Comparator comparator) ：根据指定的比较器进行排序（一般使用匿名内部类）
  • 没有带索引的方法，所以不能使用普通for循环遍历
  • 由于是Set集合，所以不包含重复元素的集合

  自然排序Comparable的使用
  学生类

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;
        }
    
        @Override
        public int compareTo(Student s) {
    //        return 0;
    //        return 1;
    //        return -1;
            //按照年龄从小到大排序
           int num = this.age - s.age;
    //        int num = s.age - this.age;
            //年龄相同时，按照姓名的字母顺序排序
           int num2 = num==0?this.name.compareTo(s.name):num;
            return num2;
        }
    }

测试类

 public class TreeSetDemo02 {
        public static void main(String[] args) {
            //创建集合对象
            TreeSet<Student> ts = new TreeSet<Student>();
    
            //创建学生对象
            Student s1 = new Student("xishi", 29);
            Student s2 = new Student("wangzhaojun", 28);
            Student s3 = new Student("diaochan", 30);
            Student s4 = new Student("yangyuhuan", 33);
    
            Student s5 = new Student("linqingxia",33);
            Student s6 = new Student("linqingxia",33);
    
            //把学生添加到集合
            ts.add(s1);
            ts.add(s2);
            ts.add(s3);
            ts.add(s4);
            ts.add(s5);
            ts.add(s6);
    
            //遍历集合
            for (Student s : ts) {
                System.out.println(s.getName() + "," + s.getAge());
            }
        }
    }

比较器排序Comparator的使用
学生类

    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;
        }
    }

测试类
public class TreeSetDemo {
public static void main(String[] args) {
//创建集合对象
TreeSet ts = new TreeSet(new Comparator() {
@Override
public int compare(Student s1, Student s2) {
//this.age - s.age
//s1,s2
int num = s1.getAge() - s2.getAge();
int num2 = num == 0 ? s1.getName().compareTo(s2.getName()) : num;
return num2;
}
});

        //创建学生对象
        Student s1 = new Student("xishi", 29);
        Student s2 = new Student("wangzhaojun", 28);
        Student s3 = new Student("diaochan", 30);
        Student s4 = new Student("yangyuhuan", 33);

        Student s5 = new Student("linqingxia",33);
        Student s6 = new Student("linqingxia",33);

        //把学生添加到集合
        ts.add(s1);
        ts.add(s2);
        ts.add(s3);
        ts.add(s4);
        ts.add(s5);
        ts.add(s6);

        //遍历集合
        for (Student s : ts) {
            System.out.println(s.getName() + "," + s.getAge());
        }
    }
}