ConcurrentModificationException产生原因的情况解析

来源：互联网发布：2017年优化设计答案编辑：程序博客网时间：2024/05/21 08:51

产生这个异常，归根结底的原因是因为，一个list或者集合在遍历的同时进行了写或者删除操作，改变了 list的大小：

private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;

public boolean hasNext() {
return cursor != size;
}

@SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
}

public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();

try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}

final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}

}

造成这个现象的原因：

1 简单直接的原因，遍历的时候进行了增删操作

for (String str : list) {

list.add(s);

list.remove(0);

}

2. 还有一种情况就是一个list 在多线程环境先，被不同的线程在遍历的同时，进行了增删操作

/**
* 中文转汉语拼音
* 支持多音字
*/
public class HanyuPinyinHelper {

private static StringBuffer buffer;
private static List<String> list;
private static Properties p;
private static boolean isSimple;

static{
buffer = new StringBuffer();
list = new ArrayList<String>();
p = new Properties();
isSimple=false;
try {
p.load(new BufferedInputStream(HanyuPinyinHelper.class
.getResourceAsStream("/hanyu_pinyin.txt")));
} catch (IOException e) {
e.printStackTrace();
}
}

public static String[] getHanyuPinyins(char c) {
int codePointOfChar = c;
String codepointHexStr = Integer.toHexString(codePointOfChar)
.toUpperCase();
String str = (String) p.get(codepointHexStr);
return str.split(",");
}

/**
* @param str 需要转换的字符串
* @param isSimple true简拼，false全拼
* @return 该字符串转换后的所有组合
*/
public static List<String> hanyuPinYinConvert(String str,boolean isSimpleFlag) {
if (str == null || "".equals(str))
return null;
isSimple=isSimpleFlag;
list.clear();
buffer.delete(0, buffer.length());
convert(0, str);
return list;
}

/**
* @param str 需要转换的字符串
* @return 该字符串转换后的所有组合，包含全拼和简拼
*/
public static List<String> hanyuAllPinYinConvert(String str) {
if (str == null || "".equals(str))
return null;
list.clear();
buffer.delete(0, buffer.length());
isSimple=true;
convert(0, str);
buffer.delete(0, buffer.length());
isSimple=false;
convert(0, str);
return list;
}

private static void convert(int n, String str) {
if (n == str.length()) {// 递归出口
String temp=buffer.toString();
if(!list.contains(temp)){
list.add(buffer.toString());
}
return;
} else {
char c = str.charAt(n);
if (0x3007 == c || (0x4E00 <= c && c <= 0x9FA5)) {// 如果该字符在中文UNICODE范围
String[] arrayStrings = getHanyuPinyins(c);
if (arrayStrings == null) {
buffer.append(c);
convert(n + 1, str);
} else if (arrayStrings.length == 0) {
buffer.append(c);
convert(n + 1, str);
} else if (arrayStrings.length == 1) {
if(isSimple){
if(!"".equals(arrayStrings[0])){
buffer.append(arrayStrings[0].charAt(0));
}
}else{
buffer.append(arrayStrings[0]);
}
convert(n + 1, str);
} else {
int len;
for (int i = 0; i < arrayStrings.length; i++) {
len = buffer.length();
if(isSimple){
if(!"".equals(arrayStrings[i])){
buffer.append(arrayStrings[i].charAt(0));
}
}else{
buffer.append(arrayStrings[i]);
}
convert(n + 1, str);
buffer.delete(len, buffer.length());
}
}
} else {// 非中文
buffer.append(c);
convert(n + 1, str);
}
}
}

public static void main(String[] args) {
List list1 = HanyuPinyinHelper.hanyuAllPinYinConvert("瞿乐底");
System.out.println(list1);

}

}

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