关于Map表循环过程删除操作出现的java.util.ConcurrentModificationException 异常
使用Iterate
List list = new ArrayList();list.add("a");list.add("b");list.add("c");//for结构 自动生成for (Iterator iterator = list.iterator(); iterator.hasNext();) {String s = (String) iterator.next();if(s.equals("b")){iterator.remove();}}System.out.println(list.size());以下代码会抛出异常
package tristan;import java.util.HashMap;import java.util.Map;public class Test {public static void main(String[] args) {Map<String,String> map = new HashMap<String, String>();map.put("1", "a1");map.put("2", "a2");map.put("3", "a3");map.put("4", "a4");map.put("5", "a5");for(String key : map.keySet()){if("a2".equals(map.get(key))){map.remove(key);}}System.out.println(map.size());}}应该深拷贝一个tmpMap，在迭代的过程中，对tmpMap进行remove操作
之后将map 赋值为 tmpMap.
package tristan;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;import java.util.HashMap;import java.util.Map;public class Test {public static void main(String[] args) throws Exception {Map<String,String> map = new HashMap<String, String>();map.put("1", "a1");map.put("2", "a2");map.put("3", "a3");map.put("4", "a4");map.put("5", "a5");Map<String,String> tmpMap = (Map<String, String>) clone(map);for(String key : map.keySet()){if("a2".equals(map.get(key))){tmpMap.remove(key);}}map = tmpMap;System.out.println(map.size());}public static Object clone(Object obj) throws Exception {ByteArrayOutputStream byteOut = new ByteArrayOutputStream();ObjectOutputStream outStream = new ObjectOutputStream(byteOut);outStream.writeObject(obj);ByteArrayInputStream byteIn = new ByteArrayInputStream(byteOut.toByteArray());ObjectInputStream inStream = new ObjectInputStream(byteIn);return inStream.readObject();}}但是这种写法可能有未知的问题， 就像四国中 灭掉一家时出现的问题一样。
最好是用下列方法
package tristan;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class Test {public static void main(String[] args) throws Exception {Map<String,String> map = new HashMap<String, String>();map.put("1", "a1");map.put("2", "a2");map.put("3", "a3");map.put("4", "a4");map.put("5", "a5");List<String> delList = new ArrayList<String>();for(String key : map.keySet()){if("a2".equals(map.get(key))){delList.add(key);}}for(String key : delList){map.remove(key);}System.out.println(map.size());}}谢谢latent同学的建议，最好还是采用Iterate来做，List Set也适用
import java.util.ArrayList;import java.util.HashMap;import java.util.HashSet;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Map.Entry;import java.util.Set;public class Test {public static void main(String[] args) throws Exception {testMap();}public static void testSet() {Set<String> set = new HashSet<String>();set.add("a1");set.add("a2");set.add("a3");set.add("a4");set.add("a5");Iterator<String> it = set.iterator();while (it.hasNext()) {String v = it.next();if ("a2".equals(v)) {it.remove();}}for (String v : set) {System.out.println(v);}}public static void testList() {List<String> list = new ArrayList<String>();list.add("a1");list.add("a2");list.add("a3");list.add("a4");list.add("a5");Iterator<String> it = list.iterator();while (it.hasNext()) {String v = it.next();if ("a2".equals(v)) {it.remove();}}for (String v : list) {System.out.println(v);}}public static void testMap() {Map<String, String> map = new HashMap<String, String>();map.put("1", "a1");map.put("2", "a2");map.put("3", "a3");map.put("4", "a4");map.put("5", "a5");/*Set<Entry<String, String>> set = map.entrySet(); Iterator<Entry<String, String>> it = set.iterator(); while (it.hasNext()) { String v = it.next().getValue(); if (v.equals("a2")) { it.remove(); } } */ Set<String> set = map.keySet();Iterator<String> it = set.iterator();while (it.hasNext()) {String k = it.next();if (map.get(k).equals("a2")) {it.remove();}}for (Map.Entry<String, String> e : map.entrySet()) {System.out.println(e.getValue());}}} 1 楼 latent 2012-01-11 import java.util.Iterator;import java.util.Map;
import java.util.HashMap;
import java.util.Map.Entry;
import java.util.Set;
public class Test {
public static void main(String[] args) {
Map<String,String> map = new HashMap<String, String>();
map.put("1", "a1");
map.put("2", "a2");
map.put("3", "a3");
map.put("4", "a4");
map.put("5", "a5");
Set<Entry<String, String>> set = map.entrySet();
Iterator<Entry<String, String>> it = set.iterator();
while(it.hasNext()) {
String str = it.next().getValue();
if("a2".equals(str)){
it.remove();
}
}
System.out.println(map.size());
}
} 2 楼 latent 2012-01-11 貌似 比楼主的 方便吧 迭代输出 满足条件 直接 remove 指针 3 楼 Tristan_S 2012-01-14 谢谢 latent 同学的提醒。
很久没有用到Iterate了。
Iterate来处理这种场景的确方便的多， 代码结构也更加清晰。