Collections集合操作的工具类

常用方法：

• public static < T> void sort(List list)：默认情况下是自然顺序，还可以设置比较排序
• public static < T> int binarySearch(List< ?> list,T key):二分查找
• public static < T> T max(Collection< ?> coll):最大值
• public static void reverse(List< ?> list):反转
• public static void shuffle(List< ?> list):随机置换

    package cn;

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

import cn.Student;


public class CollectionsTest {
    public static void main(String[] args) {


        List<Integer> list = new ArrayList<Integer>();
        // 添加元素
        list.add(11);
        list.add(12);
        list.add(14);
        list.add(13);
        list.add(15);
        System.out.println("------------add--------------");
        System.out.println(list);

        System.out.println("------------max--------------");
        System.out.println("max:"+Collections.max(list));

        System.out.println("------------自然sort--------------");
        Collections.sort(list);
        System.out.println(list);

        System.out.println("------------binarySearch--------------");
        System.out.println(Collections.binarySearch(list, 30));

        System.out.println("------------shuffle--------------");
        Collections.shuffle(list);
        System.out.println(list);

        System.out.println("------------reverse--------------");
        Collections.reverse(list);
        System.out.println(list);


        System.out.println("------------比较器sort--------------");

        List<Student> list2 = new ArrayList<Student>();
        // 创建元素
        Student s1 = new Student("abc", 27);
        Student s2 = new Student("abc", 29);
        Student s3 = new Student("bcd", 23);
        Student s4 = new Student("efd", 27);
        Student s5 = new Student("cfd", 22);
        Student s6 = new Student("cdf", 40);
        Student s7 = new Student("bed", 22);
        // 添加元素
        list2.add(s1);
        list2.add(s2);
        list2.add(s3);
        list2.add(s4);
        list2.add(s5);
        list2.add(s6);
        list2.add(s7);
        //如果排序既有自然排序(student 实现 Comparator接口),又有比较器排序(Collections.sort(集合，实现比较接口Comparator))，以比较器排序为主
        //比较器排序需要Collections.sort(集合，实现比较接口Comparator);
        Collections.sort(list2, new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {
                return s1.getName().compareTo(s2.getName());
            }
        });
        // 遍历
        for (Student s : list2) {
            System.out.println(s.getName() + "---" + s.getAge());
        }
    }
}

输出：
------------add--------------
[11, 12, 14, 13, 15]
------------max--------------
max:15
------------自然sort--------------
[11, 12, 13, 14, 15]
------------binarySearch--------------
-6
------------shuffle--------------
[11, 12, 14, 13, 15]
------------reverse--------------
[15, 13, 14, 12, 11]
------------比较器sort--------------
abc---27
abc---29
bcd---23
bed---22
cdf---40
cfd---22
efd---27

package cn;

/*
 * 如果一个类的元素要想能够进行自然排序，就必须实现自然排序接口
 */
public class Student implements Comparable<Student> {
    private String name;
    private int age;

    public Student() {
        super();
    }

    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 int compareTo(Student s) {
        //按照年龄排序
        int num1= this.getAge()-s.getAge();
        ////如果年龄相同，按名字排序
        int num2=num1==0?(this.getName().compareTo(s.getName())):num1;
        return num2;
    }
}