How to set Java version in Android Studio

The video show how to set Java version on Studio 3.3.1.

By default, the Java language version used to compile your project is based on your project's compileSdkVersion (because different versions of Android support different versions of Java). If necessary, you can override this default Java version by adding the following CompileOptions {} block to your build.gradle file:

android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_6
        targetCompatibility JavaVersion.VERSION_1_6
    }
}

(reference: Android Developers > Android Studio > User guide > Set the JDK version)

You can also set using Android Studio menu:
- File > Project Structure
- Select App on the left
- You can see option boxes of

sourceCompatibility vs targetCompatibility

According to Gradle documentation:

JavaVersion sourceCompatibility - Java version compatibility to use when compiling Java source. Default value: version of the current JVM in use JavaVersion. Can also set using a String or a Number, e.g. '1.5' or 1.5.
JavaVersion targetCompatibility - Java version to generate classes for. Default value: sourceCompatibility. Can also set using a String or Number, e.g. '1.5' or 1.5.

(reference: https://docs.gradle.org/current/userguide/java_plugin.html)