Map集合嵌套 4种遍历方式

一、俗称集合嵌套就是集合套集合 

二、分析 Map集合的嵌套

自定义一个类：

public class Person {
    private String name;
    private int age;
    public Person() {                         //有参和无参构造
        super();
    }
    public Person(String name, int age) {
        super();
        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;
    }
    
    @Override
    public int hashCode() {                                          //这个地方写hashcode是为了不让重复元素存入
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Person other = (Person) obj;
        if (age != other.age)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }
    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }
}

//注意事项：①导包时注意

                    ②正确使用 entryset和keyset关键字

                    ③使用迭代器遍历时 注意先创建集合，增强for正常遍历即可（因map无下标  不可以使用普通for进行遍历）

package com.oracle.demo01;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class Demo7 {

    public static void main(String[] args) {
        // 大map
        HashMap<String, HashMap<Person, String>> oracle = new HashMap<String, HashMap<Person, String>>();
        // 小map
        HashMap<Person, String> java1018 = new HashMap<Person, String>();
        HashMap<Person, String> java1227 = new HashMap<Person, String>();
        // 封装集合                                                //给小map赋值 用put关键字
        java1018.put(new Person("C罗", 34), "踢足球");  
        java1018.put(new Person("詹姆斯", 35), "打篮球");
        java1227.put(new Person("张继科", 28), "打乒乓球");
        java1227.put(new Person("朱婷", 22), "打排球");
        oracle.put("java1018", java1018);                     //给大map赋值 同样用put关键字
        oracle.put("java1227", java1227);
        // entryset +iterator遍历
        // 1.获取大的Map的大结婚猪呢个对象Set集合
        Set<Map.Entry<String, HashMap<Person, String>>> bigentrys = oracle.entrySet();//上面大map里面写的泛型是什么这里就写什么
        Iterator<Map.Entry<String, HashMap<Person, String>>> it = bigentrys.iterator();
        while (it.hasNext()) {
            Map.Entry<String, HashMap<Person, String>> bigentry = it.next();
            String bigkey = bigentry.getKey();                               //获取大对象key值
            HashMap<Person, String> smallMap = bigentry.getValue();          //获取大对象value值
            Set<Entry<Person, String>> entrySet = smallMap.entrySet();　　　　　//创建小对象集合
            Iterator<Entry<Person, String>> sit = entrySet.iterator();
            while (sit.hasNext()) {
                Entry<Person, String> e = sit.next();
                System.out.println(bigkey + "..." + e.getKey() + "..." + e.getValue());
            }
        }
        System.out.println("=========================");
        // 2. entryset 增强for遍历
        Set<Entry<String, HashMap<Person, String>>> entrySet = oracle.entrySet();
        for (Entry<String, HashMap<Person, String>> e : entrySet) {
            String bigKey = e.getKey();
            HashMap<Person, String> hashMap = e.getValue();
            Set<Entry<Person, String>> entrySet2 = hashMap.entrySet();
            for (Entry<Person, String> e5 : entrySet2) {
                System.out.println(bigKey + "..." + e5.getKey() + "..." + e5.getValue());
            }
        }
        System.out.println("3.增强for=========================");
        // 3.增强for+keyset方法
        Set<String> keySet = oracle.keySet();
        for (String s : keySet) {
            HashMap<Person, String> h = oracle.get(s);
            Set<Person> h2 = h.keySet();
            for (Person p : h2) {
                System.out.println(s + "..." + p + "..." + h.get(p));
            }
        }
        System.out.println("4.迭代器=========================");
　　　　//4. 迭代器+keyset方法
        Set<String> keySet2 = oracle.keySet();
        Iterator<String> ite = keySet2.iterator();
        while (ite.hasNext()) {
            String s = ite.next();
            HashMap<Person, String> hashMap = oracle.get(s);
            Set<Person> keySet3 = hashMap.keySet();
            Iterator<Person> it8 = keySet3.iterator();
            while (it8.hasNext()) {
                Person p1 = it8.next();
                System.out.println(s + "..." + p1 + "..." + hashMap.get(p1));
            }
        }
    }
}

欢迎各位大神指点和评论；