Collections集合

概述

• 是针对集合操作的工具类

常用方法

public static <T extends Comparable<? super T>> void sort(List<T> list):将指定的列表按升序排序
public static void reverse(List<?> list):反转指定列表中元素的顺序。
public static void shuffle(List<?> list):使用默认的随机源随机排列指定的列表。

package com.jihe.collections;

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

public class CollectionDemo001 {
    public static void main(String[] args){
        //创建集合对象
        List<Integer> list = new ArrayList<Integer>();

        //添加元素
        list.add(30);
        list.add(20);
        list.add(50);
        list.add(10);
        list.add(40);

        //public static <T extends Comparable<? super T>> void sort(List<T> list):将指定的列表按升序排序
//        Collections.sort(list);

        //public static void reverse(List<?> list):反转指定列表中元素的顺序。
//        Collections.reverse(list);

        //public static void shuffle(List<?> list):使用默认的随机源随机排列指定的列表。
        Collections.shuffle(list);

        System.out.println(list);
    }
}

案例

package com.jihe.collections.collectiondemo002;

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

/*
    需求：ArrayList存储学生对象，使用Collections对ArrayList进行排序
    要求：按照年龄从小到大排列，年龄相同时，按照名字的字母顺序排序
 */
public class CollectionDemo002 {
    public static void main(String[] args) {
        //2.创建ArrayList集合对象
        ArrayList<Student> array = new ArrayList<Student>();

        //3.创建学生对象
        Student s1 = new Student("流年", 20);
        Student s2 = new Student("碎冰", 30);
        Student s3 = new Student("冰茶", 25);
        Student s4 = new Student("l冰茶", 25);

        //4.把学生添加到集合
        array.add(s1);
        array.add(s2);
        array.add(s3);
        array.add(s4);

        //5.使用Collections对ArrayList进行排序
        //public static <T> void sort(List<T> list,Comparator<? super T> c)
        Collections.sort(array, new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {
                //主要条件：按照年龄从小到大排列
                int num = s1.getAge() - s2.getAge();
                //次要条件：年龄相同时，按照名字的字母顺序排序
                int num2 = num == 0 ? s1.getName().compareTo(s2.getName()) : num;
                return num2;
            }
        });
        //遍历集合
        for (Student s : array) {
            System.out.println(s.getName() + "," + s.getAge());
        }
    }
}

package com.jihe.collections.collectiondemo002;

public class Student {

    //1.定义学生类

        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;
        }
}

案例2

package com.jihe.collections.pokerdemo;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.TreeSet;

/*
    需求：通过程序实现过程中的洗牌，发牌和看牌
    要求：对牌进行排序
 */
public class PokerDemo002 {
    public static void main(String[] args) {
        //1.创建HashMap集合，键是编号，值是牌
        HashMap<Integer, String> hm = new HashMap<Integer, String>();

        //2.创建ArrayList集合，存储编号
        ArrayList<Integer> array = new ArrayList<Integer>();

        //3.创建花色数组和点数数组
        //定义花色数组
        String[] colors = {"♦", "♣", "♥", "♠"};
        //定义点数数组
        String[] numbers = {"3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A","2"};

        //4.从0开始往HashMap里面存储编号，并存储对应的牌，同时往ArrayList里面存储编号
        int index = 0;

        for (String number :numbers){
            for (String color :colors){
                hm.put(index,color+number);
                array.add(index);
                index++;
            }
        }
        hm.put(index,"小王");
        array.add(index);
        index++;
        hm.put(index,"大王");
        array.add(index);

        //5.洗牌(洗得是编号)，用用Collections的shuffle()方法实现
        Collections.shuffle(array);

        //6.发牌(发的也是编号，为了保证编号是排序的，创建TreeSet集合接收)
        TreeSet<Integer> liunian = new TreeSet<Integer>();
        TreeSet<Integer> bingcha = new TreeSet<Integer>();
        TreeSet<Integer> suibing = new TreeSet<Integer>();
        TreeSet<Integer> dpArray = new TreeSet<Integer>();

        for (int i = 0; i < array.size(); i++) {
            int x = array.get(i);
            if (i >= array.size() - 3) {
                dpArray.add(x);
            } else if (i % 3 == 0) {
                liunian.add(x);
            } else if (i % 3 == 1) {
                bingcha.add(x);
            } else if (i % 3 == 2) {
                suibing.add(x);
            }
        }

        //8.调用看牌方法
        lookPoker("流年",liunian,hm);
        lookPoker("冰茶",bingcha,hm);
        lookPoker("碎冰",suibing,hm);
        lookPoker("底牌",dpArray,hm);
    }

    //7.定义方法看牌(遍历TreeSet集合，获取编号：到HashMap集合找对应的牌)
    public static void lookPoker(String name,TreeSet<Integer> ts,HashMap<Integer,String> hm){
        System.out.print(name+"的牌是：");
        for (Integer key : ts){
            String poker = hm.get(key);
            System.out.print(poker+" ");
        }
        System.out.println(" ");
    }
}