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();}}}