Tutorial by Examples

Sorting lists Prior to Java 8, it was necessary to implement the java.util.Comparator interface with an anonymous (or named) class when sorting a list1: Java SE 1.2 List<Person> people = ... Collections.sort( people, new Comparator<Person>() { public int compare(Pe...

Functional Interfaces Lambdas can only operate on a functional interface, which is an interface with just one abstract method. Functional interfaces can have any number of default or static methods. (For this reason, they are sometimes referred to as Single Abstract Method Interfaces, or SAM Interf...

Method references allow predefined static or instance methods that adhere to a compatible functional interface to be passed as arguments instead of an anonymous lambda expression. Assume that we have a model: class Person { private final String name; private final String surname; ...

Sometimes you may want to have a lambda expression implementing more than one interface. This is mostly useful with marker interfaces (such as java.io.Serializable) since they don't add abstract methods. For example, you want to create a TreeSet with a custom Comparator and then serialize it and se...

There are several good examples of using lambdas as a FunctionalInterface in simple scenarios. A fairly common use case that can be improved by lambdas is what is called the Execute-Around pattern. In this pattern, you have a set of standard setup/teardown code that is needed for multiple scenarios ...

Lambdas are meant to provide inline implementation code for single method interfaces and the ability to pass them around as we have been doing with normal variables. We call them Functional Interface. For example, writing a Runnable in anonymous class and starting a Thread looks like: //Old way n...

The return method only returns from the lambda, not the outer method. Beware that this is different from Scala and Kotlin! void threeTimes(IntConsumer r) { for (int i = 0; i < 3; i++) { r.accept(i); } } void demo() { threeTimes(i -> { System.out.println(i); return...

A lambda closure is created when a lambda expression references the variables of an enclosing scope (global or local). The rules for doing this are the same as those for inline methods and anonymous classes. Local variables from an enclosing scope that are used within a lambda have to be final. Wit...

Anonymous class listener Before Java 8, it’s very common that an anonymous class is used to handle click event of a JButton, as shown in the following code. This example shows how to implement an anonymous listener within the scope of btn.addActionListener. JButton btn = new JButton("My Butto...

Traditional way interface MathOperation{ boolean unaryOperation(int num); } public class LambdaTry { public static void main(String[] args) { MathOperation isEven = new MathOperation() { @Override public boolean unaryOperation(int num) { ...

Since Java lambdas are closures, they can "capture" the values of variables in the enclosing lexical scope. While not all lambdas capture anything -- simple lambdas like s -> s.length() capture nothing and are called stateless -- capturing lambdas require a temporary object to hold the...

Starting with Java 8, you can use lambda expressions & predicates. Example: Use a lambda expressions & a predicate to get a certain value from a list. In this example every person will be printed out with the fact if they are 18 and older or not. Person Class: public class Person { p...