Post Overview: This post summarizes Java Functional Programming.

Table of Contents

• Functional Interfaces

Functional Interfaces

1. Callable<V>

• Represent a function that takes no arguments, returns a result and may throw an exception..
• Commonly used with ExecutorService or FutureTask to run computations in another thread and retrieve the result, or any object that needs to perform actions.
• Its functional method is V call() throws Exception.

2. Runnable

• Represents a function that takes no arguments and returns no result.
• Used by Thread, ExecutorService, UI framrworks (Swing, JavaFX), FutureTask, or any object that needs to perform actions.
• Its functional method is void run().

3. Predicate<T>

• Represents a function that takes one argument and returns a boolean result.
• Often used in filtering, matching, and test conditions.
• Its functional method is boolean test(T t).

4. Function<T,R>

• Represents a function that takes one argument and returns a result.
• Used anywhere you need to transform or map a value.
• Its functional method is R apply(T t).

5. Consumer<T>

• Represents a function that takes one argument and returns no result.
• Mostly used for side-effects, i.e., actions performed on each element of a collection or stream, logging, printing, updating state, etc.
• Its functional method is void accept(T t).

6. Supplier<T>

• Represents a function that takes no arguments and returns a result.
• Used when you want to generate or supply a value on demand.
• Its functional method is T get().