{"id":945,"date":"2023-06-28T22:40:44","date_gmt":"2022-09-20T18:00:42","guid":{"rendered":"https:\/\/www.silicloud.com\/ja\/blog\/index.php\/2023\/11\/30\/java-util-concurrentmodificationexception%e3%82%92%e6%97%a5%e6%9c%ac%e8%aa%9e%e3%81%a7%e8%87%aa%e7%84%b6%e3%81%ab%e8%a8%80%e3%81%84%e6%8f%9b%e3%81%88%e3%81%a6%e3%81%8f%e3%81%a0%e3%81%95%e3%81%84\/"},"modified":"2025-08-01T03:44:41","modified_gmt":"2025-07-31T18:44:41","slug":"java-util-concurrentmodificationexception%e3%82%92%e6%97%a5%e6%9c%ac%e8%aa%9e%e3%81%a7%e8%87%aa%e7%84%b6%e3%81%ab%e8%a8%80%e3%81%84%e6%8f%9b%e3%81%88%e3%81%a6%e3%81%8f%e3%81%a0%e3%81%95%e3%81%84","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/ja\/blog\/java-util-concurrentmodificationexception%e3%82%92%e6%97%a5%e6%9c%ac%e8%aa%9e%e3%81%a7%e8%87%aa%e7%84%b6%e3%81%ab%e8%a8%80%e3%81%84%e6%8f%9b%e3%81%88%e3%81%a6%e3%81%8f%e3%81%a0%e3%81%95%e3%81%84\/","title":{"rendered":"java.util.ConcurrentModificationException\u3092\u65e5\u672c\u8a9e\u3067\u81ea\u7136\u306b\u8a00\u3044\u63db\u3048\u3066\u304f\u3060\u3055\u3044\u30021\u3064\u306e\u9078\u629e\u80a2\u3067\u69cb\u3044\u307e\u305b\u3093\u3002\u2192 java.util.ConcurrentModificationException\u306f\u3001\u8907\u6570\u306e\u30b9\u30ec\u30c3\u30c9\u304b\u3089\u540c\u6642\u306b\u4fee\u6b63\u304c\u884c\u308f\u308c\u305f\u5834\u5408\u306b\u767a\u751f\u3059\u308b\u4f8b\u5916\u3067\u3059\u3002"},"content":{"rendered":"<p>Java\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u3092\u4f7f\u7528\u3057\u3066\u3044\u308b\u969b\u306e\u975e\u5e38\u306b\u4e00\u822c\u7684\u306a\u4f8b\u5916\u306f\u3001java.util.ConcurrentModificationException\u3067\u3059\u3002Java\u306e\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u306f\u3001\u30d5\u30a7\u30a4\u30eb\u30d5\u30a1\u30b9\u30c8\uff08Fail-Fast\uff09\u306a\u306e\u3067\u3001\u30a4\u30c6\u30ec\u30fc\u30bf\u3092\u4f7f\u7528\u3057\u3066\u30b9\u30ec\u30c3\u30c9\u304c\u30c8\u30e9\u30d0\u30fc\u30b9\u3057\u3066\u3044\u308b\u9593\u306b\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u304c\u5909\u66f4\u3055\u308c\u308b\u5834\u5408\u3001iterator.next()\u304cConcurrentModificationException\u3092\u30b9\u30ed\u30fc\u3057\u307e\u3059\u3002Concurrent modification exception\u306f\u3001\u30de\u30eb\u30c1\u30b9\u30ec\u30c3\u30c9\u74b0\u5883\u3060\u3051\u3067\u306a\u304f\u3001\u30b7\u30f3\u30b0\u30eb\u30b9\u30ec\u30c3\u30c9\u306eJava\u30d7\u30ed\u30b0\u30e9\u30df\u30f3\u30b0\u74b0\u5883\u3067\u3082\u767a\u751f\u3059\u308b\u3053\u3068\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n<h2>java.util.ConcurrentModificationException\u3092\u65e5\u672c\u8a9e\u3067\u8a00\u3044\u63db\u3048\u308b\u3068\u3001\u300cjava.util.ConcurrentModificationException\u300d\u3068\u306a\u308a\u307e\u3059\u3002<\/h2>\n<div><img decoding=\"async\" class=\"post-images\" title=\"\" src=\"https:\/\/cdn.silicloud.com\/blog-img\/blog\/img\/6564a3e3daa94e2bdf7c34d1\/2-0.jpg\" alt=\"java.util.ConcurrentModificationException, ConcurrentModificationException, Concurrent Modification Exception, Java ConcurrentModificationException\" \/><\/div>\n<pre class=\"post-pre\"><code>package com.scdev.ConcurrentModificationException;\r\n\r\nimport java.util.ArrayList;\r\nimport java.util.HashMap;\r\nimport java.util.Iterator;\r\nimport java.util.List;\r\nimport java.util.Map;\r\n\r\npublic class ConcurrentModificationExceptionExample {\r\n\r\n\tpublic static void main(String args[]) {\r\n\t\tList&lt;String&gt; myList = new ArrayList&lt;String&gt;();\r\n\r\n\t\tmyList.add(\"1\");\r\n\t\tmyList.add(\"2\");\r\n\t\tmyList.add(\"3\");\r\n\t\tmyList.add(\"4\");\r\n\t\tmyList.add(\"5\");\r\n\r\n\t\tIterator&lt;String&gt; it = myList.iterator();\r\n\t\twhile (it.hasNext()) {\r\n\t\t\tString value = it.next();\r\n\t\t\tSystem.out.println(\"List Value:\" + value);\r\n\t\t\tif (value.equals(\"3\"))\r\n\t\t\t\tmyList.remove(value);\r\n\t\t}\r\n\r\n\t\tMap&lt;String, String&gt; myMap = new HashMap&lt;String, String&gt;();\r\n\t\tmyMap.put(\"1\", \"1\");\r\n\t\tmyMap.put(\"2\", \"2\");\r\n\t\tmyMap.put(\"3\", \"3\");\r\n\r\n\t\tIterator&lt;String&gt; it1 = myMap.keySet().iterator();\r\n\t\twhile (it1.hasNext()) {\r\n\t\t\tString key = it1.next();\r\n\t\t\tSystem.out.println(\"Map Value:\" + myMap.get(key));\r\n\t\t\tif (key.equals(\"2\")) {\r\n\t\t\t\tmyMap.put(\"1\", \"4\");\r\n\t\t\t\t\/\/ myMap.put(\"4\", \"4\");\r\n\t\t\t}\r\n\t\t}\r\n\r\n\t}\r\n}\r\n<\/code><\/pre>\n<p>\u4e0a\u8a18\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u306f\u3001\u4ee5\u4e0b\u306e\u30b3\u30f3\u30bd\u30fc\u30eb\u30ed\u30b0\u306b\u8868\u793a\u3055\u308c\u308b\u3088\u3046\u306b\u5b9f\u884c\u3059\u308b\u3068\u3001java.util.ConcurrentModificationException\u304c\u767a\u751f\u3057\u307e\u3059\u3002<\/p>\n<pre class=\"post-pre\"><code>List Value:1\r\nList Value:2\r\nList Value:3\r\nException in thread \"main\" java.util.ConcurrentModificationException\r\n\tat java.base\/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:937)\r\n\tat java.base\/java.util.ArrayList$Itr.next(ArrayList.java:891)\r\n\tat com.scdev.ConcurrentModificationException.ConcurrentModificationExceptionExample.main(ConcurrentModificationExceptionExample.java:22)\r\n\r\n<\/code><\/pre>\n<p>\u51fa\u529b\u306e\u30b9\u30bf\u30c3\u30af\u30c8\u30ec\u30fc\u30b9\u304b\u3089\u660e\u3089\u304b\u306a\u3088\u3046\u306b\u3001\u540c\u6642\u5909\u66f4\u4f8b\u5916\u306fiterator\u306enext()\u95a2\u6570\u3092\u547c\u3073\u51fa\u3057\u305f\u3068\u304d\u306b\u767a\u751f\u3057\u307e\u3059\u3002\u5909\u66f4\u304c\u3069\u306e\u3088\u3046\u306b\u691c\u51fa\u3055\u308c\u308b\u304b\u8a73\u3057\u304f\u77e5\u308a\u305f\u3044\u5834\u5408\u3001\u305d\u306e\u5b9f\u88c5\u306fAbstractList\u30af\u30e9\u30b9\u306b\u3042\u308a\u307e\u3059\u3002\u3053\u306e\u30af\u30e9\u30b9\u3067\u306fint\u578b\u306e\u5909\u6570modCount\u304c\u5b9a\u7fa9\u3055\u308c\u3066\u3044\u307e\u3059\u3002\u3053\u306emodCount\u306f\u30ea\u30b9\u30c8\u306e\u30b5\u30a4\u30ba\u304c\u5909\u66f4\u3055\u308c\u305f\u56de\u6570\u3092\u793a\u3057\u307e\u3059\u3002modCount\u306e\u5024\u306fnext()\u306e\u547c\u3073\u51fa\u3057\u306e\u5ea6\u306b\u4f7f\u7528\u3055\u308c\u3001\u95a2\u6570checkForComodification()\u5185\u3067\u5909\u66f4\u304c\u3042\u308b\u304b\u3069\u3046\u304b\u3092\u78ba\u8a8d\u3057\u307e\u3059\u3002\u4eca\u5ea6\u306f\u30ea\u30b9\u30c8\u306e\u90e8\u5206\u3092\u30b3\u30e1\u30f3\u30c8\u30a2\u30a6\u30c8\u3057\u3066\u30d7\u30ed\u30b0\u30e9\u30e0\u3092\u518d\u5b9f\u884c\u3057\u3066\u307f\u3066\u304f\u3060\u3055\u3044\u3002\u540c\u6642\u5909\u66f4\u4f8b\u5916\u306f\u3082\u306f\u3084\u30b9\u30ed\u30fc\u3055\u308c\u306a\u3044\u3053\u3068\u304c\u308f\u304b\u308b\u3067\u3057\u3087\u3046\u3002\u51fa\u529b:<\/p>\n<pre class=\"post-pre\"><code>Map Value:3\r\nMap Value:2\r\nMap Value:4\r\n<\/code><\/pre>\n<p>\u65e2\u5b58\u306emyMap\u306e\u30ad\u30fc\u30d0\u30ea\u30e5\u30fc\u3092\u66f4\u65b0\u3057\u3066\u3044\u308b\u305f\u3081\u3001\u305d\u306e\u30b5\u30a4\u30ba\u306f\u5909\u308f\u3089\u305a\u3001ConcurrentModificationException\u306f\u767a\u751f\u3057\u307e\u305b\u3093\u3002\u51fa\u529b\u7d50\u679c\u306f\u30b7\u30b9\u30c6\u30e0\u306b\u3088\u3063\u3066\u7570\u306a\u308b\u53ef\u80fd\u6027\u304c\u3042\u308a\u307e\u3059\u3002HashMap\u306e\u30ad\u30fc\u30bb\u30c3\u30c8\u306f\u30ea\u30b9\u30c8\u306e\u3088\u3046\u306b\u9806\u5e8f\u4ed8\u3051\u3055\u308c\u3066\u3044\u307e\u305b\u3093\u306e\u3067\u3001\u30b7\u30b9\u30c6\u30e0\u306b\u3088\u3063\u3066\u51fa\u529b\u306f\u7570\u306a\u308b\u304b\u3082\u3057\u308c\u307e\u305b\u3093\u3002HashMap\u306b\u65b0\u3057\u3044\u30ad\u30fc\u30d0\u30ea\u30e5\u30fc\u3092\u8ffd\u52a0\u3059\u308b\u30b3\u30fc\u30c9\u3092\u30b3\u30e1\u30f3\u30c8\u30a2\u30a6\u30c8\u3092\u89e3\u9664\u3059\u308b\u3068\u3001ConcurrentModificationException\u304c\u767a\u751f\u3057\u307e\u3059\u3002<\/p>\n<h3>\u30de\u30eb\u30c1\u30b9\u30ec\u30c3\u30c9\u74b0\u5883\u3067ConcurrentModificationException\u3092\u56de\u907f\u3059\u308b\u305f\u3081\u306b<\/h3>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\u30ea\u30b9\u30c8\u3092\u914d\u5217\u306b\u5909\u63db\u3057\u3066\u304b\u3089\u3001\u914d\u5217\u3067\u53cd\u5fa9\u51e6\u7406\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u3053\u306e\u65b9\u6cd5\u306f\u3001\u30ea\u30b9\u30c8\u304c\u5c0f\u3055\u304b\u4e2d\u7a0b\u5ea6\u306e\u5927\u304d\u3055\u306e\u5834\u5408\u306b\u306f\u52b9\u679c\u7684\u3067\u3059\u304c\u3001\u30ea\u30b9\u30c8\u304c\u5927\u304d\u3044\u5834\u5408\u306f\u30d1\u30d5\u30a9\u30fc\u30de\u30f3\u30b9\u306b\u5927\u304d\u304f\u5f71\u97ff\u3057\u307e\u3059\u3002<\/ol>\n<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\u53cd\u5fa9\u51e6\u7406\u4e2d\u306b\u30ea\u30b9\u30c8\u3092\u30ed\u30c3\u30af\u3059\u308b\u3053\u3068\u3067\u3001\u540c\u671f\u5316\u3055\u308c\u305f\u30d6\u30ed\u30c3\u30af\u5185\u306b\u914d\u7f6e\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u305f\u3060\u3057\u3001\u3053\u306e\u30a2\u30d7\u30ed\u30fc\u30c1\u306f\u30de\u30eb\u30c1\u30b9\u30ec\u30c3\u30c9\u306e\u5229\u70b9\u3092\u5931\u3046\u305f\u3081\u3001\u63a8\u5968\u3055\u308c\u3066\u3044\u307e\u305b\u3093\u3002<\/ol>\n<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<ol>JDK1.5\u4ee5\u964d\u3092\u4f7f\u7528\u3057\u3066\u3044\u308b\u5834\u5408\u306f\u3001ConcurrentHashMap\u3068CopyOnWriteArrayList\u30af\u30e9\u30b9\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u3053\u308c\u306f\u3001\u540c\u6642\u5909\u66f4\u4f8b\u5916\u3092\u56de\u907f\u3059\u308b\u305f\u3081\u306e\u63a8\u5968\u3055\u308c\u308b\u65b9\u6cd5\u3067\u3059\u3002<\/ol>\n<h3>\u5358\u4e00\u30b9\u30ec\u30c3\u30c9\u74b0\u5883\u3067ConcurrentModificationException\u3092\u56de\u907f\u3059\u308b\u305f\u3081\u306b<\/h3>\n<p>\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u306e\u30a4\u30c6\u30ec\u30fc\u30bf remove() \u95a2\u6570\u3092\u4f7f\u7528\u3057\u3066\u3001\u57fa\u790e\u3068\u306a\u308b\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u304b\u3089\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u524a\u9664\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u305f\u3060\u3057\u3001\u3053\u306e\u5834\u5408\u3001\u30ea\u30b9\u30c8\u304b\u3089\u540c\u3058\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u524a\u9664\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u304c\u3001\u4ed6\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306f\u524a\u9664\u3067\u304d\u307e\u305b\u3093\u3002Concurrent Collection \u30af\u30e9\u30b9\u3092\u4f7f\u7528\u3057\u3066\u4f8b\u3092\u5b9f\u884c\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n<pre class=\"post-pre\"><code>package com.scdev.ConcurrentModificationException;\r\n\r\nimport java.util.Iterator;\r\nimport java.util.List;\r\nimport java.util.Map;\r\nimport java.util.concurrent.ConcurrentHashMap;\r\nimport java.util.concurrent.CopyOnWriteArrayList;\r\n\r\npublic class AvoidConcurrentModificationException {\r\n\r\n\tpublic static void main(String[] args) {\r\n\r\n\t\tList&lt;String&gt; myList = new CopyOnWriteArrayList&lt;String&gt;();\r\n\r\n\t\tmyList.add(\"1\");\r\n\t\tmyList.add(\"2\");\r\n\t\tmyList.add(\"3\");\r\n\t\tmyList.add(\"4\");\r\n\t\tmyList.add(\"5\");\r\n\r\n\t\tIterator&lt;String&gt; it = myList.iterator();\r\n\t\twhile (it.hasNext()) {\r\n\t\t\tString value = it.next();\r\n\t\t\tSystem.out.println(\"List Value:\" + value);\r\n\t\t\tif (value.equals(\"3\")) {\r\n\t\t\t\tmyList.remove(\"4\");\r\n\t\t\t\tmyList.add(\"6\");\r\n\t\t\t\tmyList.add(\"7\");\r\n\t\t\t}\r\n\t\t}\r\n\t\tSystem.out.println(\"List Size:\" + myList.size());\r\n\r\n\t\tMap&lt;String, String&gt; myMap = new ConcurrentHashMap&lt;String, String&gt;();\r\n\t\tmyMap.put(\"1\", \"1\");\r\n\t\tmyMap.put(\"2\", \"2\");\r\n\t\tmyMap.put(\"3\", \"3\");\r\n\r\n\t\tIterator&lt;String&gt; it1 = myMap.keySet().iterator();\r\n\t\twhile (it1.hasNext()) {\r\n\t\t\tString key = it1.next();\r\n\t\t\tSystem.out.println(\"Map Value:\" + myMap.get(key));\r\n\t\t\tif (key.equals(\"1\")) {\r\n\t\t\t\tmyMap.remove(\"3\");\r\n\t\t\t\tmyMap.put(\"4\", \"4\");\r\n\t\t\t\tmyMap.put(\"5\", \"5\");\r\n\t\t\t}\r\n\t\t}\r\n\r\n\t\tSystem.out.println(\"Map Size:\" + myMap.size());\r\n\t}\r\n\r\n}\r\n<\/code><\/pre>\n<p>\u4e0a\u8a18\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u306e\u51fa\u529b\u306f\u4ee5\u4e0b\u306e\u901a\u308a\u3067\u3059\u3002\u30d7\u30ed\u30b0\u30e9\u30e0\u306b\u3088\u3063\u3066ConcurrentModificationException\u304c\u6295\u3052\u3089\u308c\u3066\u3044\u306a\u3044\u3053\u3068\u304c\u5206\u304b\u308a\u307e\u3059\u3002<\/p>\n<pre class=\"post-pre\"><code>List Value:1\r\nList Value:2\r\nList Value:3\r\nList Value:4\r\nList Value:5\r\nList Size:6\r\nMap Value:1\r\nMap Value:2\r\nMap Value:4\r\nMap Value:5\r\nMap Size:4\r\n<\/code><\/pre>\n<p>\u4e0a\u8a18\u306e\u4f8b\u304b\u3089\u660e\u3089\u304b\u306a\u3088\u3046\u306b\u3001<\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>ConcurrentCollection\u306e\u30af\u30e9\u30b9\u306f\u5b89\u5168\u306b\u4fee\u6b63\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u3001ConcurrentModificationException\u3092\u30b9\u30ed\u30fc\u3057\u307e\u305b\u3093\u3002<\/ol>\n<\/li>\n<\/ol>\n<p>CopyOnWriteArrayList\u306e\u5834\u5408\u3001\u30a4\u30c6\u30ec\u30fc\u30bf\u306f\u30ea\u30b9\u30c8\u306e\u5909\u66f4\u3092\u53d7\u3051\u5165\u308c\u305a\u3001\u5143\u306e\u30ea\u30b9\u30c8\u4e0a\u3067\u52d5\u4f5c\u3057\u307e\u3059\u3002<\/p>\n<p>ConcurrentHashMap\u306e\u5834\u5408\u3001\u52d5\u4f5c\u306f\u5e38\u306b\u540c\u3058\u3067\u306f\u3042\u308a\u307e\u305b\u3093\u3002\u6761\u4ef6\u306b\u304a\u3044\u3066\u3001<br \/>\nif(key.equals(&#8220;1&#8221;)){<br \/>\nmyMap.remove(&#8220;3&#8221;);}<br \/>\n\u306a\u3089\u3070\u3001\u51fa\u529b\u306f\u6b21\u306e\u3088\u3046\u306b\u306a\u308a\u307e\u3059\uff1a<br \/>\nMap\u306e\u5024\uff1a1<br \/>\nMap\u306e\u5024\uff1anull<br \/>\nMap\u306e\u5024\uff1a4<br \/>\nMap\u306e\u5024\uff1a2<br \/>\nMap\u306e\u30b5\u30a4\u30ba\uff1a4<\/p>\n<p>\u3053\u306e\u5834\u5408\u3001\u30ad\u30fc\u300c4\u300d\u3068\u4e00\u7dd2\u306b\u8ffd\u52a0\u3055\u308c\u305f\u65b0\u3057\u3044\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u304c\u53d6\u5f97\u3055\u308c\u307e\u3059\u304c\u3001\u30ad\u30fc\u300c5\u300d\u3068\u4e00\u7dd2\u306b\u8ffd\u52a0\u3055\u308c\u305f\u6b21\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306f\u53d6\u5f97\u3055\u308c\u307e\u305b\u3093\u3002\u6b21\u306b\u6761\u4ef6\u3092\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u5909\u66f4\u3059\u308b\u3068\u3001<br \/>\nif(key.equals(&#8220;3&#8221;)){<br \/>\nmyMap.remove(&#8220;2&#8221;);}<br \/>\n\u306a\u3089\u3070\u3001\u51fa\u529b\u306f\u6b21\u306e\u3088\u3046\u306b\u306a\u308a\u307e\u3059\uff1a<br \/>\nMap\u306e\u5024\uff1a1<br \/>\nMap\u306e\u5024\uff1a3<br \/>\nMap\u306e\u5024\uff1anull<br \/>\nMap\u306e\u30b5\u30a4\u30ba\uff1a4<\/p>\n<p>\u3053\u306e\u5834\u5408\u3001\u65b0\u3057\u304f\u8ffd\u52a0\u3055\u308c\u305f\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306f\u8003\u616e\u3055\u308c\u307e\u305b\u3093\u3002ConcurrentHashMap\u3092\u4f7f\u7528\u3057\u3066\u3044\u308b\u5834\u5408\u306f\u3001\u30ad\u30fc\u30bb\u30c3\u30c8\u306b\u4f9d\u5b58\u3057\u3066\u51e6\u7406\u3055\u308c\u308b\u305f\u3081\u3001\u65b0\u3057\u3044\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u8ffd\u52a0\u3092\u907f\u3051\u3066\u304f\u3060\u3055\u3044\u3002\u306a\u304a\u3001\u540c\u3058\u30d7\u30ed\u30b0\u30e9\u30e0\u3067\u3082\u3001\u30b7\u30b9\u30c6\u30e0\u306b\u3088\u3063\u3066\u306f\u7570\u306a\u308b\u5024\u304c\u8868\u793a\u3055\u308c\u308b\u3053\u3068\u306b\u6ce8\u610f\u3057\u3066\u304f\u3060\u3055\u3044\u3002\u306a\u305c\u306a\u3089\u3001HashMap\u306e\u30ad\u30fc\u30bb\u30c3\u30c8\u306f\u9806\u5e8f\u304c\u5b9a\u307e\u3063\u3066\u3044\u306a\u3044\u304b\u3089\u3067\u3059\u3002<\/p>\n<h3>`java.util.ConcurrentModificationException`\u3092\u56de\u907f\u3059\u308b\u305f\u3081\u306b\u3001for\u30eb\u30fc\u30d7\u3092\u4f7f\u7528\u3057\u3066\u304f\u3060\u3055\u3044\u3002<\/h3>\n<p>\u3082\u3057\u30b7\u30f3\u30b0\u30eb\u30b9\u30ec\u30c3\u30c9\u74b0\u5883\u3067\u4f5c\u696d\u3057\u3066\u304a\u308a\u3001\u30ea\u30b9\u30c8\u306b\u8ffd\u52a0\u3055\u308c\u305f\u4f59\u5206\u306a\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u53d6\u308a\u6271\u3044\u305f\u3044\u306e\u3067\u3042\u308c\u3070\u3001Iterator\u3067\u306f\u306a\u304ffor\u30eb\u30fc\u30d7\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n<pre class=\"post-pre\"><code>for(int i = 0; i&lt;myList.size(); i++){\r\n\tSystem.out.println(myList.get(i));\r\n\tif(myList.get(i).equals(\"3\")){\r\n\t\tmyList.remove(i);\r\n\t\ti--;\r\n\t\tmyList.add(\"6\");\r\n\t}\r\n}\r\n<\/code><\/pre>\n<p>\u540c\u3058\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u524a\u9664\u3057\u3066\u3044\u308b\u306e\u3067\u3001\u30ab\u30a6\u30f3\u30bf\u3092\u6e1b\u3089\u3057\u3066\u3044\u307e\u3059\u3002\u3082\u3057\u6b21\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3084\u66f4\u306b\u9060\u3044\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u524a\u9664\u3059\u308b\u5834\u5408\u306f\u3001\u30ab\u30a6\u30f3\u30bf\u3092\u6e1b\u3089\u3059\u5fc5\u8981\u306f\u3042\u308a\u307e\u305b\u3093\u3002\u81ea\u5206\u3067\u8a66\u3057\u3066\u307f\u3066\u304f\u3060\u3055\u3044\u3002:) \u3055\u3089\u306b\u4e00\u3064\u6ce8\u610f\u70b9\u3068\u3057\u3066\u3001\u5143\u306e\u30ea\u30b9\u30c8\u306e\u69cb\u9020\u3092subList\u3067\u5909\u66f4\u3057\u3088\u3046\u3068\u3059\u308b\u3068ConcurrentModificationException\u304c\u767a\u751f\u3057\u307e\u3059\u3002\u7c21\u5358\u306a\u4f8b\u3067\u78ba\u8a8d\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n<pre class=\"post-pre\"><code>package com.scdev.ConcurrentModificationException;\r\n\r\nimport java.util.ArrayList;\r\nimport java.util.List;\r\n\r\npublic class ConcurrentModificationExceptionWithArrayListSubList {\r\n\r\n\tpublic static void main(String[] args) {\r\n\r\n\t\tList&lt;String&gt; names = new ArrayList&lt;&gt;();\r\n\t\tnames.add(\"Java\");\r\n\t\tnames.add(\"PHP\");\r\n\t\tnames.add(\"SQL\");\r\n\t\tnames.add(\"Angular 2\");\r\n\r\n\t\tList&lt;String&gt; first2Names = names.subList(0, 2);\r\n\r\n\t\tSystem.out.println(names + \" , \" + first2Names);\r\n\r\n\t\tnames.set(1, \"JavaScript\");\r\n\t\t\/\/ check the output below. :)\r\n\t\tSystem.out.println(names + \" , \" + first2Names);\r\n\r\n\t\t\/\/ Let's modify the list size and get ConcurrentModificationException\r\n\t\tnames.add(\"NodeJS\");\r\n\t\tSystem.out.println(names + \" , \" + first2Names); \/\/ this line throws exception\r\n\r\n\t}\r\n\r\n}\r\n<\/code><\/pre>\n<p>\u4e0a\u8a18\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u306e\u51fa\u529b\u7d50\u679c\u306f\u4ee5\u4e0b\u306e\u901a\u308a\u3067\u3059\u3002<\/p>\n<pre class=\"post-pre\"><code>[Java, PHP, SQL, Angular 2] , [Java, PHP]\r\n[Java, JavaScript, SQL, Angular 2] , [Java, JavaScript]\r\nException in thread \"main\" java.util.ConcurrentModificationException\r\n\tat java.base\/java.util.ArrayList$SubList.checkForComodification(ArrayList.java:1282)\r\n\tat java.base\/java.util.ArrayList$SubList.listIterator(ArrayList.java:1151)\r\n\tat java.base\/java.util.AbstractList.listIterator(AbstractList.java:311)\r\n\tat java.base\/java.util.ArrayList$SubList.iterator(ArrayList.java:1147)\r\n\tat java.base\/java.util.AbstractCollection.toString(AbstractCollection.java:465)\r\n\tat java.base\/java.lang.String.valueOf(String.java:2801)\r\n\tat java.base\/java.lang.StringBuilder.append(StringBuilder.java:135)\r\n\tat com.scdev.ConcurrentModificationException.ConcurrentModificationExceptionWithArrayListSubList.main(ConcurrentModificationExceptionWithArrayListSubList.java:26)\r\n<\/code><\/pre>\n<p>ArrayList\u306esubList\u306e\u30c9\u30ad\u30e5\u30e1\u30f3\u30c8\u306b\u3088\u308b\u3068\u3001\u69cb\u9020\u7684\u306a\u5909\u66f4\u306fsubList\u30e1\u30bd\u30c3\u30c9\u3067\u8fd4\u3055\u308c\u305f\u30ea\u30b9\u30c8\u306e\u307f\u3067\u8a31\u53ef\u3055\u308c\u307e\u3059\u3002\u8fd4\u3055\u308c\u305f\u30ea\u30b9\u30c8\u306e\u3059\u3079\u3066\u306e\u30e1\u30bd\u30c3\u30c9\u306f\u3001\u30d0\u30c3\u30ad\u30f3\u30b0\u30ea\u30b9\u30c8\u306e\u5b9f\u969b\u306emodCount\u304c\u671f\u5f85\u5024\u3068\u7b49\u3057\u3044\u304b\u3069\u3046\u304b\u3092\u6700\u521d\u306b\u30c1\u30a7\u30c3\u30af\u3057\u3001\u7b49\u3057\u304f\u306a\u3044\u5834\u5408\u306fConcurrentModificationException\u3092\u30b9\u30ed\u30fc\u3057\u307e\u3059\u3002<\/p>\n<p>\u5f53\u793e\u306eGitHub\u30ea\u30dd\u30b8\u30c8\u30ea\u304b\u3089\u3001\u3059\u3079\u3066\u306e\u30b5\u30f3\u30d7\u30eb\u30b3\u30fc\u30c9\u3092\u30c0\u30a6\u30f3\u30ed\u30fc\u30c9\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Java\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u3092\u4f7f\u7528\u3057\u3066\u3044\u308b\u969b\u306e\u975e\u5e38\u306b\u4e00\u822c\u7684\u306a\u4f8b\u5916\u306f\u3001java.util.ConcurrentModificationException\u3067\u3059\u3002Java\u306e\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u306f\u3001\u30d5\u30a7\u30a4\u30eb\u30d5\u30a1\u30b9\u30c8\uff08Fail-Fas [&hellip;]<\/p>\n","protected":false},"author":9,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[26,61],"class_list":["post-945","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-26","tag-61"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.5 (Yoast SEO v21.5) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>java.util.ConcurrentModificationException\u3092\u65e5\u672c\u8a9e\u3067\u81ea\u7136\u306b\u8a00\u3044\u63db\u3048\u3066\u304f\u3060\u3055\u3044\u30021\u3064\u306e\u9078\u629e\u80a2\u3067\u69cb\u3044\u307e\u305b\u3093\u3002\u2192 java.util.ConcurrentModificationException\u306f\u3001\u8907\u6570\u306e\u30b9\u30ec\u30c3\u30c9\u304b\u3089\u540c\u6642\u306b\u4fee\u6b63\u304c\u884c\u308f\u308c\u305f\u5834\u5408\u306b\u767a\u751f\u3059\u308b\u4f8b\u5916\u3067\u3059\u3002 - Blog - Silicon 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