Lambdas¶

A lambda supplies an implementation of a functional interface: an interface with one abstract method.

From iteration to behavior¶

List<Integer> values = List.of(1, 2, 3);

for (int value : values) {
    System.out.println(value);
}

values.forEach(value -> System.out.println(value));
values.forEach(System.out::println);

The repository's introductory lambda example deliberately walks through indexed loops, enhanced loops, anonymous Consumer implementations, typed lambdas, inferred lambdas, and method references.

Syntax forms¶

Runnable task = () -> System.out.println("done");
Function<String, Integer> length = text -> text.length();
BinaryOperator<Integer> add = (left, right) -> left + right;
Predicate<String> present = text -> text != null && !text.isBlank();

Braces require an explicit return when returning a value:

Function<String, Integer> length = text -> {
    int result = text.length();
    return result;
};

Variable capture¶

Lambdas can capture local variables only when those variables are final or effectively final.

int factor = 2;
Function<Integer, Integer> scale = value -> value * factor;

Method references¶

Form	Example
Static method	`Integer::parseInt`
Bound instance	`System.out::println`
Unbound instance	`String::length`
Constructor	`ArrayList::new`

Verified repository program¶

Runnable Deterministic output Java 8+

java --enable-preview \
  -cp build/classes/java/main:build/resources/main \
  nitin.LambdaExpressions.L1BasicWithListIteration

The first four lines come from progressively shorter lambda forms. The final two lines compare imperative and stream reductions.

The output is verified by scripts/verify-doc-examples.sh.

Repository examples¶

src/main/java/nitin/LambdaExpressions/L1BasicWithListIteration.java
src/main/java/nitin/LambdaExpressions
src/main/java/nitin/io/fileIO/readfiles3/FileUtils.java