java增强for循环遍历Map集合问题

package Day01;

import java.util.HashMap;import java.util.Iterator;import java.util.LinkedHashMap;import java.util.Map;import java.util.Set;import java.util.Map.Entry;import org.junit.Test;public class Day01 {@Testpublic void test1() {// 使用HashMap()存入与取出顺序不一定一致。Map m = new HashMap();m.put("1", "aaa");m.put("2", "bbb");m.put("3", "ccc");// 传统方式1取出Map集合数据，用keySet()封装只包含key的Set集合，然后用iterator迭代Set集合即可取出key。Set keys = m.keySet();Iterator it = keys.iterator();while (it.hasNext()) {String key = (String) it.next();String value = (String) m.get(key);System.out.println(key + "=" + value);}}@Testpublic void test2() {// 使用HashMap()存入与取出顺序不一定一致。Map m = new HashMap();m.put("1", "aaa");m.put("2", "bbb");m.put("3", "ccc");// 增强for循环1取出Map集合数据。for(Object obj:m.keySet()){String key=(String) obj;String value=(String) m.get(key);System.out.println(key + "=" + value);}}@Testpublic void test3() {// 使用LinkedHashMap()存入与取出顺序一致。Map m = new LinkedHashMap();m.put("1", "aaa");m.put("2", "bbb");m.put("3", "ccc");// 传统方式2取出Map集合数据，用entrySet()封装成键值对的Set集合，然后用iterator取出Map.Entry。然后在通过getKey()和getValue()方法取值Set keys = m.entrySet();Iterator iterator = keys.iterator();while (iterator.hasNext()) {Map.Entry entry = (Entry) iterator.next();String key = (String) entry.getKey();String value = (String) entry.getValue();System.out.println(key + "=" + value);}}@Testpublic void test4() {Map m = new LinkedHashMap();m.put("1", "aaa");m.put("2", "bbb");m.put("3", "ccc");// 增强for循环2取出Map集合数据，for(Object obj:m.entrySet()){Map.Entry entry=(Entry) obj;String key=(String) entry.getKey();String value=(String) entry.getValue();System.out.println(key + "=" + value);}}@Testpublic void test5() {//增强for循环只适合取数据。如果想改变数据用传统方式。int arr[]={1,2,3};for(int i:arr){i=10;}System.out.println(arr[0]);//输出仍未1for(int i=0;i