Using Java 8 Lambda expressions in Android

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What are Lambda expressions

Lambda Expressions are one of the most important features added to Java 8. Prior to Lambda Expressions, implementing functional interfaces i.e interfaces with only one abstract method has been done using syntax that may seem cumbersome and unclear. In cases like this, what we are trying to do is pass a functionality as an argument to a method, such as what happens when a button is clicked. Lambda expressions enables you to do just that, in a way that is much more compact and clear. In android for example, lambdas can replace anonymous inner class when providing event listeners.

Syntax of Lambda Expressions

A lambda expression consist of the following:

  • A comma separated list of formal parameters enclosed in parentheses. The data types of the parameters in a lambda expression can be omitted. Also the parenthesis can be omitted if there is only one parameter. For example:
TextView textView = (TextView) findViewById(;
textView.setOnLongClickListener(v -> System.out.println("Long Click"));
  • The arrow token ->
  • A body which contains a single expression or a statement block. If a single expression is specified, the java runtime evaluates the expression and then return its value. To specify a statement block, enclose statements in curly braces "{}"

Lambda Expressions in Android

To use Lambda Expressions and other Java 8 features in Android, you need to use the new Jack toolchain. Open your module level build.gradle file and add the following:

android {
  defaultConfig {
    jackOptions {
      enabled true
  compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8

sync your build.gradle file and if you are having any issue with build tools, you may need to update buildToolsVersion in your build.gradle file to "24rc4" or just download the latest Android SDK Build-tools from the SDK Manager, under the Tools (Preview channel).

Alt sdk manager build tools


Adding a click listener to a button

without lambda expression

Button button = (Button)findViewById(;
button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        Toast.makeText(this, "Button clicked", Toast.LENGTH_LONG).show();

with lambda expressions It is as simple as:

Button button = (Button)findViewById(;
button.setOnClickListener(v -> Toast.makeText(this, "Button clicked", Toast.LENGTH_LONG).show());

As we can see above, using lambda expressions makes implementing a functional interface clearer and compact. Standard functional interfaces can be found in the java.util.function package [included in Java 8]. These interfaces can be used as target types for lambda expressions and method references.

Another way to have Java 8 features in your Android app is using the RetroLambda plugin. You can check out the RetroLambda github repo here.


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