Java Lambda Expressions

lambda expressions, introduced in Java 8, allow developers to write concise, functional-style code by representing anonymous functions. They enable passing code as parameters or assigning it to variables, resulting in cleaner and more readable programs.

• Lambda expressions implement a functional interface (An interface with only one abstract function)
• Enable passing code as data (method arguments).
• Lambda expressions can access only final or effectively final variables from the enclosing scope.
• Lambdas cannot throw checked exceptions unless the functional interface declares them.

Syntax of Lambda Expressions

Java Lambda Expression has the following syntax:

(parameters) -> {
// multiple statements
}

• Parameter List: Parameters for the lambda expression
• Arrow Token (->): Separates the parameter list and the body
• Body: Logic to be executed.

Functional interface

A functional interface has exactly one abstract method. Lambda expressions provide its implementation. @FunctionalInterface annotation is optional but recommended to enforce this rule at compile time.

• A functional interface contains exactly one abstract method, but it can have multiple default and static methods.
• It is mainly used with lambda expressions and method references to enable functional programming in Java.

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Types of Lambda Parameters

There are three Lambda Expression Parameters are mentioned below:

1. Lambda with Zero Parameters

Lambda expression without any input.

Syntax:

() -> System.out.println("Zero parameter lambda");

This is a zero-parameter lambda expression!

2. Lambda with a Single Parameter

Takes one input; parentheses are optional.

Syntax:

(p) -> System.out.println("One parameter: " + p);

• It is not mandatory to use parentheses if the type of that variable can be inferred from the context.
• Parentheses are optional if the compiler can infer the parameter type from the functional interface.

All elements:
1
2
3
Even elements:
2

Note: The forEach() method internally uses the Consumer<T> functional interface, which takes one argument and performs an action.

3. Lambda Expression with Multiple Parameters

Takes more than one input; parentheses are required.

Syntax:

(p1, p2) -> System.out.println("Multiple parameters: " + p1 + ", " + p2);

9
20

Note: Lambda expressions are just like functions and they accept parameters just like functions. 

Examples in Collections / Streams

Lambda expressions are widely used with Java Collections and Streams for concise operations

All names:
Alice
Bob
Charlie
Adam

Names starting with 'A':
ALICE
ADAM

Advantages

• Concise Code: Reduce boilerplate compared to anonymous classes.
• Functional Programming: Treat functions as first-class citizens.
• Improved Readability: Code is easier to read and maintain.
• Enhanced Collections and Streams: Simplify operations like filtering, mapping, and iterating.

Common Built-in Functional Interfaces

Validity Check: Example Lambda Expressions