[Java知识库]33.Java中的Collections类

一. Collections：针对集合操作工具类

1.提供静态功能：
public static void reverse(List<?> list)：对List集合顺序反转
public static void shuffle(List<?> list)：随机置换

2.?

public static <T extends Comparable<? super T>> void sort(List<T> list)：按照自然升序排序

（针对List集合排序）
public static <T> void sort(List<T> list,Comparator<? super T> c)：按照比较器排序针对List集合

List<Student>：针对List进行自然升序排序，
? ? ? ? ? ? ? ? ? ? ? ? ? ? ?主要条件：按照学生的年龄从小到大排
? ? ? ? ? ? ? ? ? ? ? ? ? ? ?次要条件：年龄相同，比较姓名内容是否相同

public class Student_1 implements Comparable<Student_1> {
    private String name;
    private int age;

    public Student_1() {
    }

    public Student_1(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 String toString() {
        return "Student_1{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @Override
    public int compareTo(Student_1 s) {
        int num = this.age-s.age;
        int num2 = (num==0)?(this.name.compareTo(s.name)):num;
        return num2;
    }
}

import java.util.List;

public class Collectionstest {
    public static void main(String[] args) {
        List<Student_1> list =new ArrayList<>();
        Student_1 s1 = new Student_1("make",20);
        Student_1 s2 = new Student_1("jone",20);
        Student_1 s3 = new Student_1("fanxi",27);
        list.add(s1);
        list.add(s2);
        list.add(s3);

        Collections.sort(list);
        for (Student_1 s:list) {
            System.out.println(s);
        }
    }
}