你还在使用迭代器删除集合数据,out 了,Java 中函数 removeIf 不香么

用户头像
Geek_6f0746
关注
发布于: 2020 年 11 月 17 日
你还在使用迭代器删除集合数据,out了,Java 中函数removeIf 不香么



简述



Java 中 集合List,Map在for循环中时,直接删除是不允许的操作。会出现如下异常



java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1445)
at java.util.HashMap$EntryIterator.next(HashMap.java:1479)
at java.util.HashMap$EntryIterator.next(HashMap.java:1477)
at com.demo.regex.RegexTest.test2(RegexTest.java:187)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)



其中的原因也是很明确,forEach 会影响整个集合的结构,集合自身的结构发生变化,但当前又在循环的进行中,集合将无法进行循环处理,故此将会抛出异常。



解决方案一



在JDK 中有一段描述



```

The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.



```



使用迭代器可以实现结构修改的动态感知。



Map<String, String> deletes = new HashMap<>();
deletes.put("1", "1");
deletes.put("2", "2");
deletes.put("3", "3");
Iterator<Map.Entry<String, String>> iterator = set.iterator();
while (iterator.hasNext()) {
Map.Entry<String, String> entry = iterator.next();
if (entry.getKey().equals("1")) {
iterator.remove();
}
}



方案二



在Java 8 后,集合提供了removeIf函数。如果只是删除其中的数据,则推荐使用。



Map<String, String> deletes = new HashMap<>();
deletes.put("1", "1");
deletes.put("2", "2");
deletes.put("3", "3");
Set<Map.Entry<String, String>> set = deletes.entrySet();
set.removeIf(entry -> entry.getKey().equals("1"));



发布于: 2020 年 11 月 17 日阅读数: 29
用户头像

Geek_6f0746

关注

可怜之人必有可恨之处可恨之人必有可悲之苦 2018.04.08 加入

程序员一枚

评论

发布
暂无评论
你还在使用迭代器删除集合数据,out了,Java 中函数removeIf 不香么