开发中常遇到到的问题二:java.lang.ArrayIndexOutOfBoundsException
2017-12-14 15:01
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开发常见错误ArrayIndexOutOfBoundsException(越界)
这个一般都是在取值或者是赋值的时候最为常见:public class ExampleUnitTest {
private String[] data;
@Test
public void addition_isCorrect() throws Exception {
data = new String[]{}; //初始化
data[0] = "李四"; //这里就会ArrayIndexOutOfBoundsException
}
}错误:
看错误能知道data这个数组是没有给分配空间导致下标0报错,那么在初始化地方修改下代码
public class ExampleUnitTest {
private String[] data;
@Test
public void addition_isCorrect() throws Exception {
data = new String[1]; //初始化
data[0] = "李四"; //这里就会ArrayIndexOutOfBoundsException
}
}这样在运行代码就OK了;
取值也一样,比方现在data数组有下标0了,那么取下标1的数据data[1]可以吗,我们试试。public class ExampleUnitTest {
private String[] data;
@Test
public void addition_isCorrect() throws Exception {
data = new String[1]; //初始化
data[0] = "李四"; //这里就会ArrayIndexOutOfBoundsException
System.out.print(data[1]);
}
}结果:
运行就可以得李四的值,也就是data数组保存的值。
结束语:
但你在取某个集合或数组的长度大的下标数据时就会报错,但保存没有定义数组长度的时候也会报错,这是我的一个理解。
这个一般都是在取值或者是赋值的时候最为常见:public class ExampleUnitTest {
private String[] data;
@Test
public void addition_isCorrect() throws Exception {
data = new String[]{}; //初始化
data[0] = "李四"; //这里就会ArrayIndexOutOfBoundsException
}
}错误:
java.lang.ArrayIndexOutOfBoundsException: 0 at com.example.mytest.ExampleUnitTest.addition_isCorrect(ExampleUnitTest.java:29) 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$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68) at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51) at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242) at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70) 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 com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)
看错误能知道data这个数组是没有给分配空间导致下标0报错,那么在初始化地方修改下代码
public class ExampleUnitTest {
private String[] data;
@Test
public void addition_isCorrect() throws Exception {
data = new String[1]; //初始化
data[0] = "李四"; //这里就会ArrayIndexOutOfBoundsException
}
}这样在运行代码就OK了;
取值也一样,比方现在data数组有下标0了,那么取下标1的数据data[1]可以吗,我们试试。public class ExampleUnitTest {
private String[] data;
@Test
public void addition_isCorrect() throws Exception {
data = new String[1]; //初始化
data[0] = "李四"; //这里就会ArrayIndexOutOfBoundsException
System.out.print(data[1]);
}
}结果:
java.lang.ArrayIndexOutOfBoundsException: 1 at com.example.mytest.ExampleUnitTest.addition_isCorrect(ExampleUnitTest.java:30) 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$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68) at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51) at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242) at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70) 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 com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)果断的报错了,那是因为数组一个就只有一位长度,现在在去值第二位当然就报错了;(下标都是已0开始的),我们把
System.out.print(data[1]);
改为
System.out.print(data[0]);
运行就可以得李四的值,也就是data数组保存的值。
结束语:
但你在取某个集合或数组的长度大的下标数据时就会报错,但保存没有定义数组长度的时候也会报错,这是我的一个理解。
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