title: Error :- Execution failed for task ':app:dexDebug' in android studio
body: <p>I newly Android project started a new default project. Everytime I try to start the app this error occurs:</p>
  
  <p>build.gradle(Module:app)</p>
  
  <pre><code>apply plugin: 'com.android.application'
  
  android {
      compileSdkVersion 21
      buildToolsVersion "21.1.2"
  
      defaultConfig {
          applicationId "com.example.jdevani.validationdemo"
          minSdkVersion 8
          targetSdkVersion 21
          versionCode 1
          versionName "1.0"
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      compile fileTree(dir: 'libs', include: ['*.jar'])
      compile 'com.android.support:appcompat-v7:21.0.3'
  }
  </code></pre>
  
  <p>build.gradle(project:EmerGencyHelp)</p>
  
  <pre><code>// Top-level build file where you can add configuration options common to all sub-projects/modules.
  
  buildscript {
      repositories {
          jcenter()
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:1.1.0'
  
          // NOTE: Do not place your application dependencies here; they belong
          // in the individual module build.gradle files
      }
  }
  
  allprojects {
      repositories {
          jcenter()
      }
  }
  </code></pre>
  
  <p>my error is </p>
  
  <pre><code>Information:Gradle tasks [:app:assembleDebug]
  :app:preBuild UP-TO-DATE
  :app:preDebugBuild UP-TO-DATE
  :app:compileDebugNdk UP-TO-DATE
  :app:checkDebugManifest
  :app:preReleaseBuild UP-TO-DATE
  :app:prepareComAndroidSupportAppcompatV72103Library UP-TO-DATE
  :app:prepareComAndroidSupportSupportV42103Library 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
  Note: C:\Users\vfinava\Desktop\Project\EmerGencyHelp\app\src\main\java\com\example\vfinava\emergencyhelp\DataHelper.java uses unchecked or unsafe operations.
  Note: Recompile with -Xlint:unchecked for details.
  :app:preDexDebug
  :app:dexDebug
  UNEXPECTED TOP-LEVEL EXCEPTION:
  com.android.dex.DexException: Multiple dex files define Landroid/support/v4/accessibilityservice/AccessibilityServiceInfoCompatIcs;
      at com.android.dx.merge.DexMerger.readSortableTypes(DexMerger.java:596)
      at com.android.dx.merge.DexMerger.getSortedTypes(DexMerger.java:554)
      at com.android.dx.merge.DexMerger.mergeClassDefs(DexMerger.java:535)
      at com.android.dx.merge.DexMerger.mergeDexes(DexMerger.java:171)
      at com.android.dx.merge.DexMerger.merge(DexMerger.java:189)
      at com.android.dx.command.dexer.Main.mergeLibraryDexBuffers(Main.java:454)
      at com.android.dx.command.dexer.Main.runMonoDex(Main.java:303)
      at com.android.dx.command.dexer.Main.run(Main.java:246)
      at com.android.dx.command.dexer.Main.main(Main.java:215)
      at com.android.dx.command.Main.main(Main.java:106)
  
  Error:Execution failed for task ':app:dexDebug'.
  &gt; com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command 'C:\Program Files\Java\jdk1.8.0_20\bin\java.exe'' finished with non-zero exit value 2
  
  Information:BUILD FAILED
  Information:Total time: 5.684 secs
  Information:1 error
  Information:0 warnings
  Information:See complete output in console
  </code></pre>
  
  <p>please help me
  Thanks in advance,</p>