public class Main {\n public static void main(String[] args) {\n List<User> userList = new ArrayList<>();\n User tom = new User(\"tom\", 11);\n User jerry = new User(\"jerry\", 11);\n userList.add(tom);\n userList.add(jerry);\n for (User user : userList) {\n System.out.println(user);\n }\n }\n}<\/code><\/pre>\n\n\n\n\u8fd9\u6bb5\u4ee3\u7801\u8fd0\u884c\u6b63\u5e38\u3002\u4f46\u73b0\u5728\u6211\u4eec\u63d0\u51fa\u7b2c\u4e00\u4e2a\u95ee\u9898\uff1a**\u4e3a\u4ec0\u4e48\u6211\u4eec\u53ef\u4ee5\u628a `userList` \u653e\u5728\u589e\u5f3a for \u5faa\u73af\u4e2d\uff0c\u800c\u4e0d\u80fd\u628a\u5355\u4e2a `User` \u5bf9\u8c61\u653e\u8fdb\u53bb\uff1f**<\/p>\n\n\n\n
\u6bd4\u5982\u6211\u4eec\u5199\uff1a<\/p>\n\n\n\n
for (Object i : tom) { ... } \/\/ \u7f16\u8bd1\u9519\u8bef<\/p>\n\n\n\n
\u8fd9\u4f1a\u62a5\u9519\u3002\u4e3a\u4ec0\u4e48\uff1f\u6211\u4eec\u5e73\u65f6\u53ef\u80fd\u6ca1\u60f3\u8fc7\u8fd9\u4e2a\u95ee\u9898\u3002<\/p>\n\n\n\n
\u63a5\u7740\u770b\u7b2c\u4e8c\u4e2a\u95ee\u9898\uff1a\u6211\u4eec\u73b0\u5728\u6709\u4e00\u4e2a\u9700\u6c42\u2014\u2014\u5982\u679c `userList` \u4e2d\u6709\u7528\u6237\u7684\u5e74\u9f84\u662f 11\uff0c\u5c31\u5411\u5217\u8868\u4e2d\u518d\u6dfb\u52a0\u4e00\u4e2a\u65b0\u7528\u6237 `\"\u5f20\u4e09\"`\u3002\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n\n\n\n
for (User user : userList) {
if (user.getAge() == 11) {
userList.add(new User(\"zhangsan\", 3));
}
}
for(User user :userList){
System.out.println(user);
}<\/p>\n\n\n\n
\u4f46\u8fd0\u884c\u540e\u629b\u51fa\u4e86 `ConcurrentModificationException` \u5f02\u5e38\u3002\u903b\u8f91\u770b\u4f3c\u5408\u7406\uff0c\u4e3a\u4ec0\u4e48\u4f1a\u51fa\u9519\uff1f<\/p>\n\n\n\n
\u5982\u679c\u6211\u4eec\u6362\u4e00\u79cd\u5199\u6cd5\uff1a<\/p>\n\n\n\n
public class Main {\n public static void main(String[] args) {\n List<User> userList = new ArrayList<>();\n User tom = new User(\"tom\", 11);\n User jerry = new User(\"jerry\", 11);\n userList.add(tom);\n userList.add(jerry);\n long count = userList.stream().filter(user -> user.getAge() == 11).count();\n for (long i = 0; i < count; i++) {\n userList.add(new User(\"zhangsan\", 3));\n }\n for (User user : userList) {\n System.out.println(user);\n }\n }\n}<\/code><\/pre>\n\n\n\n\u8fd9\u6b21\u5374\u6210\u529f\u4e86\u3002\u4e3a\u4ec0\u4e48\u540c\u6837\u662f\u201c\u904d\u5386 + \u4fee\u6539\u96c6\u5408\u201d\uff0c\u4e00\u4e2a\u62a5\u9519\uff0c\u4e00\u4e2a\u4e0d\u62a5\u9519\uff1f<\/p>\n\n\n\n
\u5e26\u7740\u8fd9\u4e24\u4e2a\u95ee\u9898\uff0c\u6211\u4eec\u8fdb\u5165\u4eca\u5929\u7684\u8bbe\u8ba1\u6a21\u5f0f\u5b9e\u6218\u2014\u2014**\u8fed\u4ee3\u5668\u6a21\u5f0f**\u3002<\/p>\n\n\n\n
---<\/p>\n\n\n\n
\u6211\u4eec\u5148\u89e3\u51b3\u7b2c\u4e00\u4e2a\u95ee\u9898\uff1a\u4e3a\u4ec0\u4e48 `List` \u53ef\u4ee5\u7528\u4e8e\u589e\u5f3a for \u5faa\u73af\uff0c\u800c `User` \u4e0d\u884c\uff1f<\/strong><\/p>\n\n\n\n\u4ece\u9762\u5411\u5bf9\u8c61\u7684\u89d2\u5ea6\u601d\u8003\uff1a\u65e2\u7136\u6709\u4e9b\u7c7b\u53ef\u4ee5\u88ab\u904d\u5386\uff0c\u6709\u4e9b\u4e0d\u80fd\uff0c\u90a3\u662f\u5426\u53ef\u4ee5\u62bd\u8c61\u51fa\u4e00\u4e2a\u201c\u53ef\u88ab\u904d\u5386\u201d\u7684\u80fd\u529b\uff1fJava \u4e2d\u786e\u5b9e\u6709\u8fd9\u6837\u7684\u63a5\u53e3\u2014\u2014`Iterable<T>`\u3002<\/p>\n\n\n\n
\u53ea\u8981\u4e00\u4e2a\u7c7b\u5b9e\u73b0\u4e86 `Iterable<T>` \u63a5\u53e3\uff0c\u5c31\u53ef\u4ee5\u653e\u5728\u589e\u5f3a for \u5faa\u73af\u4e2d\u3002`List` \u7ee7\u627f\u81ea `Collection`\uff0c\u800c `Collection` \u53c8\u7ee7\u627f\u81ea `Iterable`\uff0c\u6240\u4ee5 `ArrayList` \u7b49\u96c6\u5408\u5929\u7136\u652f\u6301\u589e\u5f3a for \u5faa\u73af\u3002<\/p>\n\n\n\n
\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u53cd\u7f16\u8bd1\u5b57\u8282\u7801\u6765\u9a8c\u8bc1\u8fd9\u4e00\u70b9\u3002\u5f53\u6211\u4eec\u5199\uff1a<\/p>\n\n\n\n
List <User> userList =new ArrayList<>();
for (User user : userList) {
System.out.println(user);
}<\/p>\n\n\n\n
\u7f16\u8bd1\u5668\u5b9e\u9645\u5c06\u5176\u7ffb\u8bd1\u4e3a\uff1a<\/p>\n\n\n\n
Iterator<User> iterator = userList.iterator();
while (iterator.hasNext()) {
User user = iterator.next();
System.out.println(user);
}<\/p>\n\n\n\n
![\"\"](\"https:\/\/i-blog.csdnimg.cn\/direct\/4b3d366ef8bf4631b458d59148a991c7.png\")
<\/p>\n\n\n\n
\u4e5f\u5c31\u662f\u8bf4\uff0c\u589e\u5f3a for \u5faa\u73af\u7684\u672c\u8d28\u662f\uff1a**\u8c03\u7528\u5bf9\u8c61\u7684 `iterator()` \u65b9\u6cd5\u83b7\u53d6\u8fed\u4ee3\u5668\uff0c\u7136\u540e\u7528 `hasNext()` \u548c `next()` \u904d\u5386\u5143\u7d20**\u3002<\/p>\n\n\n\n
public class Main {\n public static void main(String[] args) {\n List<User> userList = new ArrayList<>();\n for (User user : userList) {\n System.out.println(user);\n \/\/ a b c\n }\n\n Iterator<User> iterator = userList.iterator();\n while (iterator.hasNext()) {\n User user = iterator.next();\n System.out.println(user);\n \/\/ a b c\n }\n }\n}<\/code><\/pre>\n\n\n\n\u90a3\u4e48\uff0c\u53ea\u8981\u6211\u4eec\u7684 `User` \u7c7b\u5b9e\u73b0 `Iterable<String>` \u63a5\u53e3\uff0c\u7406\u8bba\u4e0a\u4e5f\u53ef\u4ee5\u88ab\u904d\u5386\u3002\u8fd9\u6837\u89e3\u51b3\u7a7a\u6307\u9488\u95ee\u9898\u4e86\uff0c\u8fed\u4ee3\u5668\u7a76\u6781\u8fed\u4ee3\u4ec0\u4e48\u5462\uff1fIterable\u548cIterator\uff08\u91cc\u9762\u6709hasNext\u548cnext\u548cremove\u548c\u9ed8\u8ba4\u5b9e\u73b0default\uff09<\/p>\n\n\n\n
\u6211\u4eec\u5c1d\u8bd5\u8ba9 `User` \u5b9e\u73b0 `Iterable<String>`\uff1a<\/p>\n\n\n\n
public class User implements Iterable<String> {\n private String name;\n private int age;\n\n @Override\n public Iterator<String> iterator() {\n return new UserIte();\n }\n\n public User(String name, int age) {\n this.name = name;\n this.age = age;\n }\n\n public String getName() {\n return name;\n }\n\n public void setName(String name) {\n this.name = name;\n }\n\n public int getAge() {\n return age;\n }\n\n public void setAge(int age) {\n this.age = age;\n }\n\n @Override\n public String toString() {\n return \"User{\" +\n \"name='\" + name + '\\'' +\n \", age=\" + age +\n '}';\n }\n\n\n class UserLite implements Iterable<String> {\n \n @Override\n public boolean hasNext(){\n return false;\n }\n\n @Override\n public String next(){\n return \"\";\n }\n \n}<\/code><\/pre>\n\n\n\nuser\u91cc\u9762\u6709\u4e24\u4e2a\u5c5e\u6027\uff0c\u53ea\u8981\u6211\u4eec\u628a\u4e24\u4e2a\u5c5e\u6027\u8d70\u5b8c\u4e86\u3002\u56e0\u6b64\u6211\u4eec\u8bbe\u7acb\u4e00\u4e2acount=2<\/p>\n\n\n\n
class UserLite implements Iterator<String> {\n int count = 2;\n\n @Override\n public boolean hasNext() {\n return count > 0;\n }\n\n @Override\n public String next() {\n count--;\n if (count == 1) {\n return User.this.name;\n }\n if (count == 0) {\n return User.this.age + \"\";\n }\n throw new NoSuchElementException();\n }\n}<\/code><\/pre>\n\n\n\n\u73b0\u5728\u6211\u4eecmain\u91cc\u9762\u521b\u5efa\u4e00\u4e2a `User` \u5bf9\u8c61\uff1a<\/p>\n\n\n\n
User zhangsan = new User(\"\u5f20\u4e09\", 25);
for (String s : zhangsan) {
System.out.println(s);
}<\/p>\n\n\n\n
\u8fd0\u884c\u6210\u529f\uff01\u8f93\u51fa `\"\u5f20\u4e09\"` \u548c `\"25\"`\u3002\u8bf4\u660e\u6211\u4eec\u901a\u8fc7\u5b9e\u73b0 `Iterable` \u548c `Iterator`\uff0c\u8ba9\u4e00\u4e2a\u666e\u901a\u7c7b\u4e5f\u5177\u5907\u4e86\u53ef\u8fed\u4ee3\u7684\u80fd\u529b\u3002<\/p>\n\n\n\n
---<\/p>\n\n\n\n
\u63a5\u4e0b\u6765\u89e3\u51b3\u7b2c\u4e8c\u4e2a\u95ee\u9898\uff1a**\u4e3a\u4ec0\u4e48\u8fb9\u904d\u5386\u8fb9\u4fee\u6539\u96c6\u5408\u4f1a\u629b `ConcurrentModificationException`\uff1f**<\/p>\n\n\n\n
\u6211\u4eec\u518d\u6b21\u67e5\u770b\u5b57\u8282\u7801\u6216\u6e90\u7801\u3002`ArrayList` \u7684 `iterator()` \u65b9\u6cd5\u8fd4\u56de\u4e00\u4e2a\u5185\u90e8\u7c7b `Itr`\uff0c\u5b83\u7ef4\u62a4\u4e86\u4e00\u4e2a `cursor`\uff08\u6e38\u6807\uff09\u548c\u4e00\u4e2a `expectedModCount`\u3002<\/p>\n\n\n\n
`expectedModCount` \u662f\u5728\u521b\u5efa\u8fed\u4ee3\u5668\u65f6\uff0c\u5c06\u5f53\u524d `modCount`\uff08\u4fee\u6539\u6b21\u6570\uff09\u590d\u5236\u8fc7\u6765\u7684\u3002\u6bcf\u6b21\u8c03\u7528 `next()` \u65f6\uff0c\u90fd\u4f1a\u68c0\u67e5\u5f53\u524d `modCount` \u662f\u5426\u7b49\u4e8e `expectedModCount`\u3002\u5982\u679c\u4e0d\u7b49\uff0c\u8bf4\u660e\u96c6\u5408\u5728\u904d\u5386\u8fc7\u7a0b\u4e2d\u88ab\u5916\u90e8\u4fee\u6539\u4e86\uff0c\u5c31\u4f1a\u629b\u51fa `ConcurrentModificationException`\u3002<\/p>\n\n\n\n
\u8fd9\u4e5f\u662f\u4e3a\u4ec0\u4e48\u6211\u4eec\u5728\u904d\u5386\u65f6\u8c03\u7528 `list.add()` \u4f1a\u5931\u8d25\u3002<\/p>\n\n\n\n
\u800c\u5f53\u6211\u4eec\u4f7f\u7528 `stream().count()` \u65f6\uff0c\u662f\u5728\u904d\u5386\u4e4b\u524d\u5c31\u5b8c\u6210\u4e86\u7edf\u8ba1\uff0c\u6ca1\u6709\u5728\u8fed\u4ee3\u8fc7\u7a0b\u4e2d\u4fee\u6539\u96c6\u5408\uff0c\u6240\u4ee5\u4e0d\u4f1a\u89e6\u53d1\u5f02\u5e38\u3002<\/p>\n\n\n\n
\u5982\u679c\u6211\u4eec\u771f\u7684\u60f3\u5728\u904d\u5386\u4e2d\u4fee\u6539\uff0c\u53ef\u4ee5\u5728 `add` \u540e\u7acb\u5373 `break`\uff0c\u786e\u4fdd\u4e0d\u518d\u8c03\u7528 `next()`\uff1a<\/p>\n\n\n\n
public class Main {\n public static void main(String[] args) {\n List<User> list = new ArrayList<>();\n list.add(new User(\"tom\", 11));\n list.add(new User(\"jerry\", 12));\n\n Iterator<User> iterator = list.iterator();\n while (iterator.hasNext()) {\n User user = iterator.next();\n if (user.getAge() == 12) {\n list.add(new User(\"zhangsan\", 3));\n break;\n }\n }\n for (User user : list) {\n System.out.println(user);\n }\n }\n}<\/code><\/pre>\n\n\n\n\u8fd9\u6837\u5c31\u4e0d\u4f1a\u629b\u5f02\u5e38\uff0c\u56e0\u4e3a `next()` \u4e0d\u4f1a\u518d\u88ab\u8c03\u7528\uff0c`checkForComodification` \u4e5f\u4e0d\u4f1a\u6267\u884c\u3002<\/p>\n\n\n\n
---<\/p>\n\n\n\n
\u73b0\u5728\u6211\u4eec\u8fdb\u5165\u5b9e\u6218\uff1a\u5047\u8bbe\u6709\u4e00\u4e2a\u6587\u4ef6 `demo.user`\uff0c\u5185\u5bb9\u5982\u4e0b\uff1a<\/p>\n\n\n\n
[alice,10]
[boy,16]
[candy,15]
[oiioi,3]
[tom,2]<\/p>\n\n\n
[jemmy,1]<\/p>\n\n\n\n
\u6bcf\u884c\u8868\u793a\u4e00\u4e2a\u7528\u6237\uff0c\u683c\u5f0f\u4e3a `[name,age]`\u3002\u6211\u4eec\u9700\u8981\u89e3\u6790\u8fd9\u4e2a\u6587\u4ef6\uff0c\u751f\u6210\u591a\u4e2a `User` \u5bf9\u8c61\u8fdb\u884c\u5904\u7406\u3002<\/p>\n\n\n\n
\u5e38\u89c4\u505a\u6cd5\u662f\uff1a<\/p>\n\n\n\n
public class Main {\n public static void main(String[] args) throws IOException {\n List<User> userList = new ArrayList<>();\n readFiles((User user) -> {\n System.out.println(user);\n userList.add(user);\n });\n }\n\n private static void readFiles(Consumer<User> userConsumer) throws IOException {\n List<String> lines = Files.readAllLines(new File(\"demo.user\").toPath());\n for (String line : lines) {\n String midString = line.substring(1, line.length() - 1);\n String[] split = midString.split(\",\");\n String name = split[0];\n int age = Integer.parseInt(split[1]);\n User user = new User(name, age);\n userConsumer.accept(user);\n }\n }\n}<\/code><\/pre>\n\n\n\n\u4f46\u5982\u679c\u6587\u4ef6\u5f88\u5927\uff0c\u4e00\u6b21\u6027\u8bfb\u5165\u5185\u5b58\u53ef\u80fd\u5bfc\u81f4 OOM\u3002\u800c\u4e14\u5982\u679c\u6211\u4eec\u8981\u591a\u6b21\u5904\u7406\u8fd9\u4e9b\u7528\u6237\uff0c\u6bcf\u6b21\u90fd\u8981\u91cd\u65b0\u8bfb\u6587\u4ef6\u3002<\/p>\n\n\n\n
\u6211\u4eec\u53ef\u4ee5\u7528**\u8fed\u4ee3\u5668\u6a21\u5f0f**\u91cd\u6784\uff1a\u8ba9\u6587\u4ef6\u672c\u8eab\u6210\u4e3a\u4e00\u4e2a\u53ef\u8fed\u4ee3\u5bf9\u8c61\u3002<\/p>\n\n\n\n
\u6211\u4eec\u521b\u5efa\u4e00\u4e2a\u7c7b `UserFile`\uff0c\u5b9e\u73b0 `Iterable<User>`\uff1a<\/p>\n\n\n\n
public class UserFile implements Iterable<User> {\n\n private final File file;\n\n @Contracture(true)\n public UserFile(File file) {\n this.file = file;\n }\n\n @Override\n public Iterator<User> iterator() {\n return null;\n }\n}\n\nclass UserFileIterator implements Iterator<User> {\n\n List<User> userList = loadUsersFromFile();\n\n private List<User> loadUsersFromFile() {\n try {\n return Files.readAllLines(file.toPath()).stream().map(String line -> {\n String midString = line.substring(1, line.length() - 1);\n String[] split = midString.split(\",\");\n return new User(split[0], Integer.parseInt(split[1]));\n }).collect(Collectors.toList());\n } catch (IOException e) {\n e.printStackTrace();\n }\n }\n\n @Override\n public boolean hasNext() {\n return cursor!=userList.size();\n }\n\n @Override\n public User next() {\n if(cursor>=userList.size()){\n throw new NoSuchElementException();\n }\n int currentIndex = cursor;\n cursor++;\n return userList.get(currentIndex);\n }\n}<\/code><\/pre>\n\n\n\n```<\/p>\n\n\n\n
\u4f7f\u7528\u65b9\u5f0f\uff1a<\/p>\n\n\n\n
```java
UserFile userFile = new UserFile(Paths.get(\"demo.user\"));
for (User user : userFile) {
System.out.println(user);
}
```<\/p>\n\n\n\n
\u8fd9\u6837\u6211\u4eec\u5c31\u5b9e\u73b0\u4e86\u201c\u6587\u4ef6\u5373\u96c6\u5408\u201d\u7684\u62bd\u8c61\uff0c\u7528\u6237\u65e0\u9700\u5173\u5fc3\u6570\u636e\u6765\u6e90\u3002<\/p>\n\n\n\n
---<\/p>\n\n\n\n
\u6700\u540e\u7559\u4e00\u4e2a\u601d\u8003\u9898\uff1a
\u5982\u679c\u6587\u4ef6\u975e\u5e38\u5927\uff0c\u4e0a\u8ff0\u5b9e\u73b0\u4ecd\u7136\u4f1a\u5c06\u6240\u6709\u6570\u636e\u52a0\u8f7d\u5230\u5185\u5b58\u4e2d\u3002\u4f60\u80fd\u5426\u4fee\u6539 `UserFileIterator`\uff0c\u4f7f\u5176**\u5206\u6279\u8bfb\u53d6**\uff0c\u6bd4\u5982\u6bcf\u6b21\u53ea\u8bfb\u4e00\u884c\uff0c\u7528\u5b8c\u5373\u5f03\uff0c\u4ece\u800c\u8282\u7701\u5185\u5b58\uff1f\u63d0\u793a\uff1a\u4e0d\u8981\u4e00\u6b21\u6027 `Files.lines().collect()`\uff0c\u800c\u662f\u5728 `hasNext()` \u548c `next()` \u4e2d\u52a8\u6001\u8bfb\u53d6\u3002 \u200b<\/p>\n","protected":false},"excerpt":{"rendered":"
\u8fd9\u662f\u4e00\u4e2a\u65b0\u7684\u5de5\u7a0b\u3002\u6211\u4eec\u5148\u521b\u5efa\u4e00\u4e2a `User` \u7c7b\uff0c\u6dfb\u52a0\u4e24\u4e2a\u5c5e\u6027\uff1a`name` \u548c `age`\uff0c\u52a0\u4e0a\u6784\u9020\u51fd\u6570\uff0c\u5e76\u91cd\u5199 `toStr …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"emotion":"","emotion_color":"","title_style":"","license":"","footnotes":""},"categories":[2],"tags":[35],"class_list":["post-1240","post","type-post","status-publish","format-standard","hentry","category-2","tag-35"],"_links":{"self":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/1240","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1240"}],"version-history":[{"count":1,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/1240\/revisions"}],"predecessor-version":[{"id":1241,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/1240\/revisions\/1241"}],"wp:attachment":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1240"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1240"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1240"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}