1、Collections

    • Collections概述和使用
      • 针对集合操作的工具类

    • Collections类的常用方法

      • public static > void sort(List 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

        1. /*
        2. ArrayList存储学生对象，使用Collections对ArrayList进行排序
        3. 要求：按照年龄从小到大排序，年龄相同时，按照姓名的字母顺序排序
        4. */
        5. public class CollectionsDemo {
        6. public static void main(String[] args) {
        7.    //创建对象
        8.    ArrayList<Student> arr = new ArrayList<>();
        9.    Student s1 = new Student("a", 18);
        10.    Student s2 = new Student("b", 20);
        11.    Student s3 = new Student("c", 19);
        12.    Student s4 = new Student("d", 19);
        14.    arr.add(s1);
        15.    arr.add(s2);
        16.    arr.add(s3);
        17.    arr.add(s4);
        19.    Collections.sort(arr, new Comparator<Student>() {
        20.        @Override
        21.        public int compare(Student o1, Student o2) {
        22.            int num = o1.getAge() - o2.getAge();
        23.            int num2 = num == 0 ? o1.getName().compareTo(o2.getName()) : num;
        24.            return num2;
        25.        }
        26.    });
        28.    for (Student s : arr) {
        29.        System.out.println(s.getName() + ", " + s.getAge());
        30.    }
        32. }
        33. }

    • 模拟斗地主

      • image.png ```java / 通过程序实现斗地主过程中的洗牌，发牌和看牌 / public class PokerDemo { public static void main(String[] args) { //创建牌盒 ArrayList arrayList = new ArrayList<>();

        //创建牌 //牌有四种花色，每种花色都有2-A的牌，大小王 //创建花色数组和数字数组，进行拼接得到需要的牌 String[] colors = {“♥”, “♦”, “♠”, “♣”}; String[] numbers = {“2”, “3”, “4”, “5”, “6”, “7”, “8”, “9”, “10”, “J”, “Q”, “K”, “A”}; for (String color : colors) {

        1.    for (String number : numbers) {
        2.        arrayList.add(color + number);
        3.    }

        } arrayList.add(“大王”); arrayList.add(“小王”);

        //洗牌 //使用Collections的shuffle方法 Collections.shuffle(arrayList);

        //发牌 //创建三个人的牌盒，以及底牌的牌盒并把牌分发给四个牌盒 ArrayList arrayList1 = new ArrayList<>(); ArrayList arrayList2 = new ArrayList<>(); ArrayList arrayList3 = new ArrayList<>(); ArrayList dpArrayList = new ArrayList<>(); for (int i = 0; i < arrayList.size(); i++) {

        1.    String poker = arrayList.get(i);
        2.    //如果是最后三张牌则放入底牌
        3.    if (i >= arrayList.size() - 3) {
        4.        dpArrayList.add(poker);
        5.    } else if (i % 3 == 0) {
        6.        arrayList1.add(poker);
        7.    } else if (i % 3 == 1) {
        8.        arrayList2.add(poker);
        9.    } else if (i % 3 == 2) {
        10.        arrayList3.add(poker);
        11.    }

        }

        System.out.println(“王小恒的牌是：” + arrayList1); System.out.println(“王中恒的牌是：” + arrayList2); System.out.println(“王大恒的牌是：” + arrayList3); System.out.println(“底牌是：” + dpArrayList);

    1. }

    }

    2. - **模拟斗地主升级版**
    3.    - ![image.png](https://cdn.nlark.com/yuque/0/2022/png/26723396/1652147795444-f2c9d8d5-ed40-4ab5-b288-7a59a5066bf2.png#clientId=u139c8eb2-e3d8-4&crop=0&crop=0&crop=1&crop=1&from=paste&height=322&id=u177ba762&margin=%5Bobject%20Object%5D&name=image.png&originHeight=643&originWidth=1219&originalType=binary&ratio=1&rotation=0&showTitle=false&size=171445&status=done&style=none&taskId=ue58ae32c-e8b5-4af8-a834-0e3d85d5657&title=&width=609.5)
    4. ```java
    5. /*
    6.     模拟斗地主升级版
    7.     通过程序实现斗地主过程中的洗牌，发牌和看牌
    8.     对牌进行排序
    9.  */
    10. public class PokerDemoPlus {
    11.     public static void main(String[] args) {
    12.         //创建索引和牌之间的映射
    13.         HashMap<Integer, String> hm = new HashMap<>();
    15.         //创建牌
    16.         StringBuilder sb = new StringBuilder();
    17.         String[] colors = {"♥", "♦", "♠", "♣"};
    18.         String[] numbers = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
    19.         for (String number : numbers) {
    20.             for (String color : colors) {
    21.                 sb.append(color + number);
    22.                 sb.append(" ");
    23.             }
    24.         }
    25.         sb.append("大王 ");
    26.         sb.append("小王");
    27.         String poker = sb.toString();
    28.         String[] pokers = poker.split(" "); //得到牌的一个String数组
    29.         //新建牌盒，牌盒中存储索引值即map中的键
    30.         ArrayList<Integer> arr = new ArrayList<>();
    31.         //将索引与牌对应，并把索引存入牌盒
    32.         for (int i = 0; i < pokers.length; i++) {
    33.             hm.put(i, pokers[i]);
    34.             arr.add(i);
    35.         }
    37.         //洗牌 将索引值打乱
    38.         Collections.shuffle(arr);
    40.         //发牌，需要创建牌盒
    41.         TreeSet<Integer> ts1 = new TreeSet<>();
    42.         TreeSet<Integer> ts2 = new TreeSet<>();
    43.         TreeSet<Integer> ts3 = new TreeSet<>();
    44.         TreeSet<Integer> dpTs = new TreeSet<>();
    46.         for (int i = 0; i < arr.size(); i++) {
    47.             int pokerIndex = arr.get(i);
    48.             //最后三张牌放入底牌盒
    49.             if (i >= arr.size() - 3) {
    50.                 dpTs.add(pokerIndex);
    51.             } else if (i % 3 == 0) {
    52.                 ts1.add(pokerIndex);
    53.             } else if (i % 3 == 1) {
    54.                 ts2.add(pokerIndex);
    55.             } else if (i % 3 == 2) {
    56.                 ts3.add(pokerIndex);
    57.             }
    58.         }
    60.         lookPoker("王小恒", ts1, hm);
    61.         lookPoker("王中恒", ts2, hm);
    62.         lookPoker("王大恒", ts3, hm);
    63.         lookPoker("底牌", dpTs, hm);
    66.         System.out.println("");
    67.     }
    69.     public static void lookPoker(String name, TreeSet<Integer> ts, HashMap<Integer, String> hm) {
    70.         System.out.print(name + "的牌是：");
    71.         for (int index : ts) {
    72.             System.out.print(hm.get(index) + " ");
    73.         }
    74.         System.out.println();
    75.     }
    76. }