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"));

来源：oschina

链接：https://my.oschina.net/u/3247419/blog/4720371

标签

junit