Java Functional Interfaces — Free Java Tutorial
Learn Java Functional Interfaces in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.
TL;DR: Learn Java Functional Interfaces in Java with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.
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Java Functional Interfaces in Java
A functional interface has exactly one abstract method. It can be implemented with a lambda expression or method reference. The @FunctionalInterface annotation is optional but recommended.
Built-in functional interfaces (java.util.function): Predicate<T> (T -> boolean), Function<T,R> (T -> R), Consumer<T> (T -> void), Supplier<T> (() -> T), BiFunction<T,U,R> (T,U -> R), UnaryOperator<T> (T -> T).
Predicate has and(), or(), negate() methods for composition. Function has andThen() and compose() for chaining transforms.
Custom functional interfaces allow you to define domain-specific function types: @FunctionalInterface interface Validator<T> { boolean validate(T value); }
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