Using lambda's with android. With help from gradle-retrolambda

build.gradle

buildscript {
    repositories {
        jcenter()
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.1.1'
        classpath 'me.tatarka:gradle-retrolambda:3.2.3'
    }
}

apply plugin: 'com.android.application'
apply plugin: 'me.tatarka.retrolambda'

repositories {
    jcenter()
    mavenCentral()
}

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.0"

    defaultConfig {
        applicationId "com.newboston.app"
        minSdkVersion 11
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:23.0.1'
}

MainActivity.java

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        loginBtn = (Button) findViewById(R.id.login_btn);
        loginBtn.setOnClickListener((View) -> login());

        Log.i(TAG, "onCreate finished");
    }

    private void login() {
           Context context = getApplicationContext();
           CharSequence text = "Hello toast!";
           int duration = Toast.LENGTH_SHORT;

           Toast toast = Toast.makeText(context, text, duration);
           toast.show();
    }