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：

[java]
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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();
}
}
}

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();
}
}
}