Open up your build.gradle file located here:
This is the old way of writing the dependency libraries (for gradle version 2 and below):
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile files('libs/volley.jar')
compile 'com.android.support:support-v4:21.+'
}
This is the new (right) way of importing the dependencies for gradle version 3:
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
testImplementation 'junit:junit:4.12'
implementation files('libs/volley.jar')
implementation 'com.android.support:support-v4:21.+'
}