初学AndroidStudio，运行第一个HelloWorld的问题，请指教！

Gradle Console提示的信息如下：
FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':app:transformClassesWithDexForDebug'.
> com.android.build.api.transform.TransformException: com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command 'D:\Java\jdk1.7.0_80\bin\java.exe'' finished with non-zero exit value 2
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
BUILD FAILED
Total time: 5 mins 5.29 secs

这个不碍事

后来在那个......\HelloWorld\app\build\outputs\apk下找到了打包的app-debug.apk，新问题又来了，为什么要加个debug?是编译的问题吗？