我刚刚在win 7上安装了Android studio，并想编译第一个示例代码，但编译失败

Executing tasks: [:app:assembleDebug]

Configuration on demand is an incubating feature.

:app:preBuil
:app:compileDebugNdk UP-TO-DATE
:app:preDebugBuild
:app:checkDebugManifest
:app:preReleaseBuild
:app:prepareComAndroidSupportAppcompatV72102Library UP-TO-DATE
:app:prepareComAndroidSupportSupportV42102Library UP-TO-DATE
:app:prepareDebugDependencies
:app:compileDebugAidl UP-TO-DATE
:app:compileDebugRenderscript UP-TO-DATE
:app:generateDebugBuildConfig UP-TO-DATE
:app:generateDebugAssets UP-TO-DATE
:app:mergeDebugAssets UP-TO-DATE
:app:generateDebugResValues UP-TO-DATE
:app:generateDebugResources UP-TO-DATE
:app:mergeDebugResources UP-TO-DATE
:app:processDebugManifest UP-TO-DATE
:app:processDebugResources UP-TO-DATE
:app:generateDebugSources UP-TO-DATE
:app:compileDebugJava UP-TO-DATE
:app:preDexDebug

Den angivne sti blev ikke fundet. (The specified path was not found.)

 FAILED

Den angivne sti blev ikke fundet. (The specified path was not found.)

FAILURE: Build failed with an exception.

* What went wrong:

Execution failed for task ':app:preDexDebug'.

> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
C:\Users\Sigmac\AppData\Local\Android\sdk\build-tools\21.1.1\dx.bat --dex --output 
C:\Users\Sigmac\AndroidStudioProjects\Voting\app\build\intermediates\pre-dexed\debug
\classes-b6f615fe9376219a5b11445078329964f51dafd9.jar C:\Users\Sigmac
\AndroidStudioProjects\Voting\app\build\intermediates\exploded-aar\com.android.support
\appcompat-v7\21.0.2\classes.jar

Error Code:
1

Output:
Den angivne sti blev ikke fundet. (The specified path was not found.)

* 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: 30.911 secs

Den angivne sti blev ikke fundet. (The specified path was not found.)

我已经测试过这个eKist：C：\用户\Sigmac\AppData\本地\Android\sdk\build-tools\21.1.1\dx. bat

这个文件夹是独立的，但它是emty C：\用户\Sigmac\AndroidStudioProjects\投票\应用\构建\中间体\预编译\调试\

而这个手C：\用户\Sigmac\AndroidStudioProjects\投票\应用\构建\中间体\爆炸-aar\com.android.support\appcompat-v7\21.0.2\类. jar

我有谷歌和搜索这个网站，但找不到解决方案

--stacktrace、--info或--debug不会更改结果

我直接从cmd尝试了相同的结果，我尝试了""路径

有人能给我指出解决办法吗？