单线程情况下遍历ArrayList的ConcurrentModificationException的问题

看到一段程序在单线程方式下运行还抛出ConcurrentModificationException,大概看了下是在以for-each方式遍历ArrayList时,循环内部又对集合作修改引起,换种方式遍历即可解决。
所以在使用JDK集合类的Iterator时,还要对其实现原理有大概了解。由于一直都没有了解集合遍历,标记下><
code:

@Test
public void testConcurrentModificationException() throws Exception {
try {
List arr = new ArrayList();
arr.add("1");arr.add("2");arr.add("3");

/* 不会抛出ConcurrentModificationException,
* 可在单线程情况下使用此遍历方式
*/
for(int i=0; i arr.add("4");
if(i==1)
break;
}
System.out.println(arr);

/* 抛出ConcurrentModificationException,
* 因为for-each内部以Iterator方遍历集合,
* 由ArrayList创建的Iterator是以快速失败的方式处理遍历过程中的并发修改问题
* @see: java.util.AbstractList.Itr.next()
*/
for(String i : arr) {
arr.add("4");
if(i.equals("2"))
break;
}
System.out.println(arr);
} catch(Exception e) {
e.printStackTrace();
Assert.fail();
}
}

运行结果

[1, 2, 3, 4, 4]
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
at java.util.AbstractList$Itr.next(AbstractList.java:343)
at com.ys.kj.service.impl.UpgradeServiceTest.testConcurrentModificationException(UpgradeServiceTest.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:30)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

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