java - Error :- Execution failed for task ':app:dexDebug' in android studio

Question

I newly Android project started a new default project. Everytime I try to start the app this error occurs:

build.gradle(Module:app)

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'
}

build.gradle(project:EmerGencyHelp)

// 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()
    }
}

my error is

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:UsersvfinavaDesktopProjectEmerGencyHelpappsrcmainjavacomexamplevfinavaemergencyhelpDataHelper.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'.
> com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command 'C:Program FilesJavajdk1.8.0_20injava.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

please help me Thanks in advance,

Answer 1

Probably you dont add suport-v4 library correctly in your project.
Check this :

1. you have add this library to all modules that need it (If you have more than module in your project like main module and library module).
2. Check that you dont add this library twice.

Finally if this didn't resolve your problem try to remove this library from your imported libraries list and your project modules dependency list and import and add it again from one source to your project , then try rebuild the project or restart the IDE.
I hope this way can help you :)