集合的练习

1. 案例一：自动选择器：

    

    

    

    

2. 案例一代码实现：

   import java.util.*;
   
   public class text {
       public static void main(String[] args) {
           //第一种实现方式
           List<String> list=new ArrayList<>();
           Collections.addAll(list,"张三","李四","王五","赵六","前妻");
           Random random=new Random();
           int i = random.nextInt(list.size());
           String s=list.get(i);
           System.out.println(s);
           //第二种实现方式
           Collections.shuffle(list);
           System.out.println(list.get(0));
   
       }
   }

3. 案例2：

    

    

4. 案例二代码实现：

   import java.util.ArrayList;
   import java.util.Collections;
   import java.util.Random;
   
   public class text2 {
       public static void main(String[] args) {
           //创建集合
           ArrayList<Integer> arrayList=new ArrayList<>();
           //添加数据
           Collections.addAll(arrayList,1,1,1,1,1,1,1);
           Collections.addAll(arrayList,0,0,0);
           //打乱集合中的数据
           Collections.shuffle(arrayList);
           //从集合中随机抽取0或1
           Random random=new Random();
           int index = random.nextInt(arrayList.size());
           int number=arrayList.get(index);
           //创建两个集合分别储存男生和女生的名字
           ArrayList<String> boyList=new ArrayList<>();
           ArrayList<String> girlList=new ArrayList<>();
           //添加数据
           Collections.addAll(boyList,"刘宇坚","李进","许德俊","周文杰","张宇坤");
           Collections.addAll(boyList,"邱静","张芊","熊伟仪");
           //根据0和1从集合中取值
           if (number==1){
               int bindex=random.nextInt(boyList.size());
               System.out.println(boyList.get(bindex));
           }else {
               int gindex=random.nextInt(boyList.size());
               System.out.println(boyList.get(gindex));
           }
       }
   }

5. 案例3：

    

    

6. 案例3代码实现;

    

    

7. 案例4：

    

    

8. 案例5：

   import java.util.*;
   
   public class text4 {
       public static void main(String[] args) {
           HashMap<String, ArrayList<String>> hashMap=new HashMap<>();
           ArrayList<String> list=new ArrayList<>();
           Collections.addAll(list,"万年","上饶");
           hashMap.put("江西",list);
           Set<Map.Entry<String, ArrayList<String>>> entries = hashMap.entrySet();
           for (Map.Entry<String, ArrayList<String>> entry : entries) {
               String key = entry.getKey();
               ArrayList<String> value = entry.getValue();
               StringBuilder stringBuilder=new StringBuilder();
               for (String s : value) {
                   System.out.println(s);
   stringBuilder.append(s);
               }
               System.out.println(key+stringBuilder.toString());
   
   
           }
   
       }
   }