版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/lisulong1/article/details/81875048
ensureCapacity(int minCapacity)
这个方法实现的是将数组进行扩容，扩容至原数组的1.5被，如果minCapacity大于原数组的1.5被则扩容到minCapacity；
但是ArrayList中有size属性，这个值并未变化，所以当你通过index新增数组时会出现数组越界；
因为ArrayList内部是通过size属性进行数组索引界限检查的；
java.lang.IndexOutOfBoundsException: Index: 15, Size: 10
at java.util.ArrayList.rangeCheckForAdd(ArrayList.java:643)
at java.util.ArrayList.add(ArrayList.java:455)
at com.sl.activiti.test.CommonTest.test1(CommonTest.java:18)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
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.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:67)