如何在Java中迭代地图或者HashMap
时间：2020-02-23 14:34:21 来源:igfitidea点击:
在本教程中，我们将看到我们如何在Java中迭代地图。
有四种方法可以迭代地图，HashMap或者Treemap。
如果在迭代时删除元素，则第1和第3个选项将抛出java.util.concurrentmodificationException。
如果我们了解HashMap的内部工作，那么我们可能更容易迭代HashMap
让我们举个例子：
- iteratemapmain.java.
package org.igi.theitroad;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
public class IterateMapMain {
public static void main(String args[])
{
//HashMap with Country as key and capital as value
HashMap<String,String> countryCapitalMap=new HashMap<String,String>();
countryCapitalMap.put("Netherlands","Delhi");
countryCapitalMap.put("Japan","Tokyo");
countryCapitalMap.put("France","Paris");
countryCapitalMap.put("Russia","Moscow");
//Iterating Using keySet() and for each loop
System.out.println("Iterating Using keySet() and for each loop");
for (String countryKey:countryCapitalMap.keySet()) {
System.out.println("Country:"+ countryKey +" and Capital:"+countryCapitalMap.get(countryKey));
}
System.out.println("-----------------------------");
//Iterating Using keySet() and java iterator
System.out.println("Iterating Using keySet() and java Iterator");
Iterator countryKeySetIterator=countryCapitalMap.keySet().iterator();
while(countryKeySetIterator.hasNext()){
String countryKey=countryKeySetIterator.next();
System.out.println("Country:"+ countryKey +" and Capital:"+countryCapitalMap.get(countryKey));
}
System.out.println("-----------------------------");
//Iterating Using entrySet() and for each loop
System.out.println("Iterating Using entrySet() and for each loop");
for (Entry<String,String> entry:countryCapitalMap.entrySet()) {
System.out.println("Country:"+ entry.getKey() +" and Capital:"+entry.getValue());
}
System.out.println("-----------------------------");
//Iterating Using entrySet() and java iterator
System.out.println("Iterating Using entrySet() and and java Iterator");
Iterator<Entry<String,String>> entryIterator=countryCapitalMap.entrySet().iterator();
while(entryIterator.hasNext())
{
Entry<String,String> entry=entryIterator.next();
System.out.println("Country:"+ entry.getKey() +" and Capital:"+entry.getValue());
}
System.out.println("-----------------------------");
}
}
运行它，我们将获取以下输出：
Iterating Using keySet() and for each loop Country:France and Capital:Paris Country:Russia and Capital:Moscow Country:Japan and Capital:Tokyo Country:Netherlands and Capital:Delhi ---------------------------- Iterating Using keySet() and java Iterator Country:France and Capital:Paris Country:Russia and Capital:Moscow Country:Japan and Capital:Tokyo Country:Netherlands and Capital:Delhi ---------------------------- Iterating Using entrySet() and for each loop Country:France and Capital:Paris Country:Russia and Capital:Moscow Country:Japan and Capital:Tokyo Country:Netherlands and Capital:Delhi ---------------------------- Iterating Using entrySet() and and java Iterator Country:France and Capital:Paris Country:Russia and Capital:Moscow Country:Japan and Capital:Tokyo Country:Netherlands and Capital:Delhi ----------------------------
