Lambda expressions and functional programming in Java

13 Oct 2023

Java 8 introduced a new feature called lambda expressions, which brought functional programming capabilities to the language. Lambda expressions allow developers to write more concise and expressive code, making it easier to work with collections, handle events, and implement functional interfaces. In this blog post, we will explore lambda expressions and functional programming in Java.

What is Functional Programming?
Introduction to Lambda Expressions
Functional Interfaces
Using Lambda Expressions
Common Use Cases for Lambda Expressions
Conclusion

What is Functional Programming?

Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids changing state and mutable data. In contrast to object-oriented programming, which focuses on objects and their interactions, functional programming emphasizes the process of applying functions to inputs and producing outputs without side effects.

Introduction to Lambda Expressions

Lambda expressions in Java are anonymous functions - functions without a name - that can be passed around as arguments or stored in variables. They enable a more concise syntax for writing functional-style code. A lambda expression consists of the following parts:

(parameters) -> expression

Where:

parameters represent the input arguments to the function.
-> acts as a separator between the parameters and the expression.
expression is the body of the function, which is executed and returned as the result.

For example, a simple lambda expression () -> System.out.println("Hello, World!") represents a function that takes no arguments and prints “Hello, World!” to the console.

Functional Interfaces

Lambda expressions are most commonly used in the context of functional interfaces. A functional interface is an interface that contains only one abstract method. Java provides many built-in functional interfaces such as Predicate, Function, and Consumer. These interfaces represent common functional patterns and can be used with lambda expressions.

interface MyFunctionalInterface {
    void doSomething();
}

Above is an example of a simple functional interface with a single abstract method doSomething(). Lambda expressions can be used to implement this interface concisely:

MyFunctionalInterface myLambda = () -> System.out.println("Doing something...");

Using Lambda Expressions

Lambda expressions can be used in various scenarios. Some common use cases include:

Filtering Collections

List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");
List<String> result = names.stream()
                          .filter(name -> name.startsWith("A"))
                          .collect(Collectors.toList());
System.out.println(result); // Output: [Alice]

Event Handling

button.addActionListener(event -> System.out.println("Button clicked!"));

Multithreading

Runnable myRunnable = () -> {
    // Perform some action
};
new Thread(myRunnable).start();

Common Use Cases for Lambda Expressions

Lambda expressions are particularly useful in functional-style programming, where operations such as mapping, filtering, and reducing collections are common. They promote code clarity, reduce boilerplate, and enable developers to write more concise and expressive code.

Conclusion

Lambda expressions have revolutionized how we write code in Java. They bring the power of functional programming to the language, allowing developers to write more expressive and concise code. By leveraging lambda expressions, Java developers can embrace functional programming principles and unlock the benefits of more maintainable and readable code. So, start exploring this powerful feature and enhance your Java programming skills.

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