Java中遍历Map的几种方法

方法分为两类:

一类是基于map的Entry;map.entrySet();

一类是基于map的key;map.keySet()

而每一类都有两种遍历方式:

a.利用迭代器 iterator;

b.利用for-each循环;

代码举例如下

package cn.wzb;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry; //循环遍历map的方法
public class TestMap {
public static void main(String[] args) {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("a", 1);
map.put("b", 2);
map.put("c", 3); // JDK1.4中
// 遍历方法一 hashMap.entrySet() 遍历
System.out.println("方法一");
Iterator<Entry<String, Integer>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<String, Integer> entry = it.next();
String key = entry.getKey();
Integer value = entry.getValue();
System.out.println("key = " + key + "; value = " + value);
} System.out.println(""); // JDK1.5中,应用新特性For-Each循环 // 遍历方法二
System.out.println("方法二");
for (Map.Entry<String, Integer> entry : map.entrySet()) {
String key = entry.getKey();
String value = entry.getValue().toString();
System.out.println("key =" + key + " value = " + value);
}
System.out.println(""); // 遍历方法三 hashMap.keySet().iterator() 遍历
System.out.println("方法三");
for (Iterator<String> i = map.keySet().iterator(); i.hasNext(); ) {
String key = i.next();
System.out.println(" key = " + key + "; value = " + map.get(key));
} /*
for (Iterator<Integer> i = map.values().iterator(); i.hasNext(); ) {
Integer value = i.next();
System.out.println(value));// 循环输出value
}
*/
/*
for(Integer value : map.values() ) {
System.out.println("value = " + value);
}
*/ System.out.println("");
// 遍历方法四 Hashmap.keySet()遍历
System.out.println("方法四");
for (String key : map.keySet()) {
System.out.println("key = " + key + "; value = " + map.get(key));
}
System.out.println(); // java如何遍历Map <String, ArrayList> map = new HashMap <String, ArrayList<Integer> >();
System.out.println("java 遍历Map <String, ArrayList<Integer> map = new HashMap <String, ArrayList<Integer>>();");
System.out.println("方法一:");
Map<String, List<Integer> > mapList = new HashMap <String, List<Integer> >();
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(5);
mapList.put("aaa", list);
mapList.put("bbb", list); Set<String> keys = mapList.keySet();
Iterator<String> iterator = keys.iterator();
while (iterator.hasNext()) {
String key = iterator.next();
System.out.println(key + " : "); List<Integer> arrayList = mapList.get(key);
for (Integer i : arrayList) {
System.out.print(i + ", ");
}
System.out.println();
} System.out.println("方法二:"); for (Map.Entry<String, List<Integer> > entry : mapList.entrySet()) {
String key = entry.getKey();
System.out.println(key + " : "); List<Integer> values = (List<Integer>) entry.getValue();
for (Integer value : values) {
System.out.print(value + ", ");
}
System.out.println();
}
}
}

  

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