1：输入字符串统计其中各个字符出现的次数

package java_practice;

import java.util.HashMap;
import java.util.Scanner;
import java.util.Set;

//实现一个统计输入字符串中出现某字符的个数
public class HashMapDemo2 {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入字符串");
        String line = sc.nextLine();
        //创建HashMap集合
        HashMap<Character, Integer> hm = new HashMap<>();
        for (int i = 0; i < line.length(); i++) {
            char key = line.charAt(i);
            Integer value = hm.get(key);
            if (value == null) {
                hm.put(key, 1);
            } else {
                value++;
                hm.put(key, value);
            }
        }
        StringBuilder sb = new StringBuilder();
        Set<Character> keyset = hm.keySet();
        for(Character  key:keyset)
        {
            Integer value = hm.get(key);
            sb.append(key).append("(").append(value).append(")");


        }
        String result = sb.toString();
        System.out.println(result);

    }
}

2：模拟斗地主发牌洗牌

–jgdabc(兰舟千帆)

版本一

package demo;

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

public class PokerDemo {
    public static void main(String[] args) {
        ArrayList<String> array = new ArrayList<>();
        //创建HashMap,键是编号，值是牌
        HashMap<Integer, String> hm = new HashMap<>();
        //创建ArrayList,存储编号

        //定义花色数组
        String[] colors = {"♦", "♥", "♣", "♠"};
        String[] numbers = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
        //
        for (String color : colors)
            for (String number : numbers) {
                array.add(color + number);
    }
        array.add("小王");
        array.add("大王");
        //System.out.println(array);
        //进行洗牌
        Collections.shuffle(array);
        // System.out.println(array);
        //创建三个玩家
        ArrayList<String> lqx = new ArrayList<String>();
        ArrayList<String> ly = new ArrayList<>();
        ArrayList<String> fqy = new ArrayList<>();
        //创建底牌
        ArrayList<String> dp = new ArrayList<>();
        //进行发牌
        for (int i = 0; i < array.size(); i++) {
            String s = array.get(i);
            if (i >= array.size() - 3) {
                dp.add(s);
            } else if (i % 3 == 0) {
                lqx.add(s);

            } else if (i % 3 == 1) {
                ly.add(s);
            } else if (i % 3 == 2) {
                fqy.add(s);
            }
        }
        lookPoker("林青霞",lqx);
        lookPoker("柳岩",ly);
        lookPoker("风清扬",fqy);
        lookPoker("底牌",dp);
    }

        //看牌的方法
        public static void lookPoker(String name,ArrayList<String> array)
        {
            System.out.print(name + "的牌是:");
            for(String poker:array)
            {
                System.out.print(poker+" ");
            }
            System.out.println();
        }
        //存储编号

      
    //
    }

版本二

package demo;

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

public class PokerDemo1 {
    public static void main(String args[]) {
        //创建HashMap,键是编号，值是牌
        HashMap<Integer, String> hm = new HashMap<Integer, String>();
        //创建ArrayList。存储编号
        ArrayList<Integer> array = new ArrayList<>();
        //创建花色数组和点数数组
        String[] colors = {"♦", "♥", "♣", "♠"};
        String[] numbers = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
        //从零开始往HashMap中存储编号，并存储对应的牌，同时在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);
        Collections.shuffle(array);
        //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> lqx = new TreeSet<Integer>();
        TreeSet<Integer> ly = new TreeSet<Integer>();
        TreeSet<Integer> fqy = new TreeSet<Integer>();
        TreeSet<Integer> dp = new TreeSet<Integer>();
        for (int i = 0; i < array.size(); i++) {
            int x = array.get(i);
            if (i >= array.size() - 3) {
                dp.add(x);
            } else if (i % 3 == 0) {
                lqx.add(x);
            } else if (i % 3 == 1) {
                ly.add(x);

            } else if (i % 3 == 2) {
                fqy.add(x);
            }
        }

        lookPoker("林青霞", lqx, hm);
        lookPoker("柳岩", ly, hm);
        lookPoker("风清扬",fqy,hm);
        lookPoker("底牌",dp,hm);
    }

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