Java中集合的嵌套：嵌套集合、嵌套keySet遍历、嵌套entrySet遍历

一、嵌套集合

1、ArrayList嵌套 ArrayList

• • 
    
• ArrayList< ArrayList<String> >
• Collection< ArrayList<Integer> >
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2、Map嵌套 ArrayList

• • 
    
• HashMap<String, ArrayList<Person>>
• ArrayList< HashMap<String, String>>
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3、Map集合嵌套

• • 
    
• HashMap<String, HashMap<String,String>>
  
• HashMap<String, HashMap<Person,String>>
  
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4、代码实例

• Map 集合嵌套keySet遍历

public static void main(String[] args)
{
    /**
     * 在学生中有男孩和女孩，而男孩和女孩都有自己的编号和姓名
     * 这里将学生存储到Map集合中，把男孩和女孩也存储到Map集合中
     * 再将男孩和女孩集合嵌套进学生集合
     */
    Map<Integer,String> boys = new HashMap<>();
    Map<Integer,String> girls = new HashMap<>();
    boys.put(1,"小明");
    boys.put(2,"小强");
    boys.put(3,"小龙");
    girls.put(1,"小小");
    girls.put(2,"小花");
    girls.put(3,"小佳");
    Map<Integer,Map<Integer,String>> Student = new HashMap<>();
    Student.put(1,boys);
    Student.put(2,girls);
    System.out.println(Student);

    //调用Student集合方法keySet将键存储到Set集合
    Set<Integer> S1 = Student.keySet();
    //迭代Set集合
    Iterator<Integer> Stu_it = S1.iterator();
    while (Stu_it.hasNext()) {
        //it.next获取出来的是Set集合元素,Student集合的键
        Integer Stu_key = Stu_it.next();
        //Student集合的方法get获取值,值是一个Map集合
        Map<Integer, String> Stu_value = Student.get(Stu_key);
        Set<Integer> S2 = Stu_value.keySet();
        Iterator<Integer> it = S2.iterator();
        while (it.hasNext()) {
            Integer key = it.next();
            String value = Stu_value.get(key);
            System.out.println(key + "=" + value);
        }
    }
    System.out.println("==================================");

    //使用增强for进行遍历
    for(Integer Stu__key : Student.keySet())
    {
        Map<Integer,String> Stu__value = Student.get(Stu__key);
        for (Integer key : Stu__value.keySet())
        {
            String value = Stu__value.get(key);
            System.out.println(key + "=" +value);
        }
    }
}

• Map 集合嵌套entrySet遍历

public static void main(String[] args)
{
    /**
     * 在学生中有男孩和女孩，而男孩和女孩都有自己的编号和姓名
     * 这里将学生存储到Map集合中，把男孩和女孩也存储到Map集合中
     * 再将男孩和女孩集合嵌套进学生集合
     */
    Map<Integer,String> boys = new HashMap<>();
    Map<Integer,String> girls = new HashMap<>();
    boys.put(1,"小明");
    boys.put(2,"小强");
    boys.put(3,"小龙");
    girls.put(1,"小小");
    girls.put(2,"小花");
    girls.put(3,"小佳");
    Map<Integer,Map<Integer,String>> Student = new HashMap<>();
    Student.put(1,boys);
    Student.put(2,girls);
    System.out.println(Student);

    //调用Student集合方法entrySet方法,将Student集合的键值对关系对象,存储到Set集合
    Set<Map.Entry<Integer,Map<Integer,String>>> Stu = Student.entrySet();
    //迭代器迭代Set集合
    Iterator<Map.Entry<Integer,Map<Integer,String>>> Stu_it = Stu.iterator();
    while (Stu_it.hasNext())
    {
        //Stu_it.next方法,取出的是Student集合的键值对关系对象
        Map.Entry<Integer, Map<Integer, String>> Stu_entry = Stu_it.next();
        Integer Stu_key = Stu_entry.getKey();
        Map<Integer,String> Stu_value = Stu_entry.getValue();
        System.out.println(Stu_key + "=" + Stu_value);
        //调用Person集合entrySet方法,键值对关系对象存储Set集合
        Set<Map.Entry<Integer,String>> S = Stu_value.entrySet();
        //迭代Set集合
        Iterator<Map.Entry<Integer,String>> it = S.iterator();
        while (it.hasNext())
        {
            //获取boys和girls中键值对对象并将其取出
            Map.Entry<Integer,String> entry = it.next();
            Integer key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + "="+ value);
        }
    }
    //使用增强for进行遍历
    for(Map.Entry<Integer, Map<Integer, String>> Stud : Student.entrySet())
    {
        Integer Stu__key = Stud.getKey();
        Map<Integer,String> Stu__value = Stud.getValue();
        System.out.println(Stu__key + "=" + Stu__value);
        for(Map.Entry<Integer,String> M : Stu__value.entrySet())
        {
            Integer key_ = M.getKey();
            String value_ = M.getValue();
            System.out.println(key_ + "=" + value_);
        }
    }
}