Collections

操作Set、List和Map等集合的工具类

排序操作：

• reverse(List):反转List集合中元素的顺序
• shuffle(List):对List集合元素进行随机排序
• sort：根据List元素的自然排序对集合元素进行升序排序
• sort(List,Comparator):根据指定的Comparator产生的顺序对List进行排序
• swap(List,int.int):将指定list集合中的元素进行交换

package exception.eee;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Coll {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("4");
        list.add("a");
        list.add("ab");
        list.add("A");

        System.out.println(list);
        Collections.reverse(list);//反转
        System.out.println(list);
        Collections.shuffle(list);
        System.out.println(list);//随机
        Collections.sort(list);
        System.out.println(list);
        Collections.swap(list, 1, 2);//根据索引交换位置
        System.out.println(list);
        System.out.println(Collections.frequency(list, "a"));//出现次数
        Collections.replaceAll(list, "a", "5");//替换
        System.out.println(list);

        System.out.println(Collections.max(list));//返回集合中最大
        System.out.println(Collections.min(list));//返回集合中最小

        Student as = new Student(44,"hsh");
        Student as1 = new Student(54,"hsh");
        Student as2 = new Student(64,"hsh");
        Student as3 = new Student(414,"hsh");

        List<Student> ob = new ArrayList<>();
        ob.add(as);
        ob.add(as1);
        ob.add(as2);
        ob.add(as3);
        System.out.println("===============");
        Student s =Collections.max(ob, new Student());
        System.out.println(s.age+s.name);

        Student s1 =Collections.min(ob, new Student());
        System.out.println(s1.age+s1.name);
        System.out.println("-----------");
        for (Student o: ob){
            System.out.println(o.age+o.name);
        }
       /* System.out.println("-------------------");
        Collections.sort(ob, new Student());
        for (Student o: ob){
            System.out.println(o.age+o.name);//升序
        }*/
    }
}

class Student implements Comparator<Student> {
int age;
String name;

    public Student(int age, String name) {
        this.age = age;
        this.name = name;
    }

    public Student() {
    }

    @Override
    public int compare(Student o1, Student o2) {
        if (o1.age> o2.age){
            return 1;
        }else if (o1.age< o2.age){
            return -1;
        }else {
            return 0;
        }
    }
}

同步控制

synchronizedXxx()方法