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