Lambda expressions were introduced in Java 8 to simplify the writing of functional interfaces. 1. The basic syntax is (parameters) -> { body }, and parameter types or brackets can be omitted according to the situation. For example, if there is no parameter, use () -> System.out.println("Hello"), use x -> System.out.println(x), use multiple parameters (x, y) -> xy; 2. The lambda can be assigned to functional interfaces such as Runnable, Consumer or Function, which replaces anonymous class writing and improves readability; 3. It is often used in combination with collections and Stream APIs, such as forEach, filter, map, etc., to make the code more concise and clear; 4. Use parameter types in combination with type inference to improve code simplicity; 5. Use method references (such as System.out::println) instead of lambdas that only call a single method, further reducing redundant code. Rational use of lambda can improve Java development efficiency and code quality.
Lambda expressions were introduced in Java 8, and they brought a more concise way to write instances of functional interfaces —interfaces with only one abstract method. If you're looking to simplify your code or work with streams and modern Java features, lambdas are essential.
Here's how to use them effectively.
Understanding the Basic Syntax
The basic structure of a lambda expression is:
(parameters) -> { body }Depending on the situation, parts of this can be omitted for brevity.
- No parameters :
() -> System.out.println("Hello") - One parameter :
x -> System.out.println(x) - Multiple parameters :
(x, y) -> xy
You can assign these directly to functional interfaces like Runnable , Consumer , or Function .
For example:
Runnable r = () -> System.out.println("Running...");This replaces the older anonymous class style:
Runnable r = new Runnable() {
public void run() {
System.out.println("Running...");
}
};It's cleaner and easier to read, especially when passing behavior as arguments.
Using Lambdas with Collections and Streams
One of the most common uses of lambda expressions is with Java Streams , which were also introduced in Java 8.
If you have a list and want to process each element, instead of writing a loop, you can do something like:
List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
names.forEach(name -> System.out.println(name));Or filter elements:
names.stream()
.filter(name -> name.startsWith("A"))
.forEach(System.out::println);This makes it easy to chain operations and keep your logic clear.
Some key interfaces to know when working with lambdas and streams:
-
Predicate<T>– used for filtering (testmethod) -
Function<T, R>– used for mapping (apply) -
Consumer<T>– for side effects (accept) -
Supplier<T>– for lazy evaluation (get)
Each of these can be implemented using a lambda, without needing custom classes.
Leveraging Type Inference and Method References
Java can often infer types from context, so you don't always need to specify them explicitly.
Instead of:
List<String> filtered = names.stream()
.filter((String name) -> name.length() > 3)
.toList();You can just write:
List<String> filtered = names.stream()
.filter(name -> name.length() > 3)
.toList();Also, if your lambda just calls an existing method, you can replace it with a method reference :
names.forEach(System.out::println);
Which is shorter than:
names.forEach(x -> System.out.println(x));
Method references come in a few forms:
-
ClassName::staticMethod -
object::instanceMethod -
ClassName::instanceMethod(used when the first argument is the instance)
They help reduce visual noise and improve readingability.
Using lambda expressions doesn't have to feel complex. Start with simple cases like replacing anonymous classes or iterating over collections, and gradually move into more advanced stream operations. Just remember to keep your lambdas short and focused — ideally doing only one thing.
Once you get used to them, they become a natural part of your Java toolkit.
Basically that's it.
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