Detailed explanation on the use of HashMap traversal in Java

This article mainly introduces the use of HashMap and traversal related information in Java development. Here is a simple example of HashMap combined with List. Friends in need can refer to it

Java Development The use and traversal of HashMap

1: A simple example of using HashMap

package com.pb.collection; 
 
import java.util.HashMap; 
import java.util.Iterator; 
import java.util.Set; 
import java.util.Map.Entry; 
 
public class HashMapDemo { 
 
  public static void main(String[] args) { 
     
    HashMap<String, String> hashMap = new HashMap<String, String>(); 
    hashMap.put("cn", "中国"); 
    hashMap.put("jp", "日本"); 
    hashMap.put("fr", "法国"); 
     
    System.out.println(hashMap); 
    System.out.println("cn:" + hashMap.get("cn")); 
    System.out.println(hashMap.containsKey("cn")); 
    System.out.println(hashMap.keySet()); 
    System.out.println(hashMap.isEmpty()); 
     
    hashMap.remove("cn"); 
    System.out.println(hashMap.containsKey("cn")); 
     
    //采用Iterator遍历HashMap 
    Iterator it = hashMap.keySet().iterator(); 
    while(it.hasNext()) { 
      String key = (String)it.next(); 
      System.out.println("key:" + key); 
      System.out.println("value:" + hashMap.get(key)); 
    } 
     
    //遍历HashMap的另一个方法 
    Set<Entry<String, String>> sets = hashMap.entrySet(); 
    for(Entry<String, String> entry : sets) { 
      System.out.print(entry.getKey() + ", "); 
      System.out.println(entry.getValue()); 
    } 
  } 
}

2: An example of combining List and HashMap implementation

import java.util.Iterator; 
import java.util.List; 
import java.util.HashMap; 
import java.util.ArrayList; 
import java.util.Map; 
import java.util.Scanner; 
import java.util.Set; 
import java.util.Map.Entry; 
/** 
 * 在不创建学生类的情况下，从键盘输入n个学生信息(学号，姓名，年龄）， 
 * 输入完成后，打印出各个学生信息 
 * @author ccna_zhang 
 * 
 */ 
public class Assignment { 
   
  public static void main(String[] args) { 
     
    //定义保存学生信息的List，元素类型为HashMap 
    List<HashMap<String, Object>> list = new ArrayList<HashMap<String, Object>>(); 
    Scanner input = new Scanner(System.in); 
     
    System.out.println("请输入学生的信息,y表示继续，n表示退出"); 
    while("y".equals(input.next())) { 
      HashMap<String, Object> map = new HashMap<String, Object>(); 
      System.out.println("请输入学号"); 
      map.put("studentno", input.next()); 
      System.out.println("请输入姓名"); 
      map.put("name", input.next()); 
      System.out.println("请输入年龄"); 
      map.put("age", input.nextInt()); 
      list.add(map); 
      System.out.println("请继续输入学生的信息,y表示继续，n表示退出"); 
    } 
     
    System.out.println("输入的学生信息为:"); 
    System.out.println("学生数量为:" + list.size()); 
     
    Iterator<HashMap<String, Object>> it = list.iterator(); 
    int i = 1; 
    while(it.hasNext()) { 
      HashMap<String, Object> stuMap = it.next(); 
      System.out.print("第" + i + "个学生的信息为"); 
      System.out.println("学号:" + stuMap.get("studentno") + " ,姓名:" + stuMap.get("name") + " ,年龄:" + stuMap.get("age")); 
    } 
  } 
}

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