Setup Steps:

1. Download and install jdk8.

2. Add the following to your project’s main build.gradle

   buildscript {
       repositories {
           mavenCentral()
       }
   
       dependencies {
           classpath 'me.tatarka:gradle-retrolambda:3.2.3'
       }
   }
   

3. Now add this to your application module’s build.gradle

   apply plugin: 'com.android.application' // or apply plugin: 'java'
   apply plugin: 'me.tatarka.retrolambda'
   

4. Add these lines to your application module’s build.gradle to inform the IDE of the language level:

   android {
       compileOptions {
           sourceCompatibility JavaVersion.VERSION_1_8
           targetCompatibility JavaVersion.VERSION_1_8
       }
   }
   

Example:

So things like this:

button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        log("Clicked");
    }
});

Become this:

button.setOnClickListener(v -> log("Clicked"));