Supplier<T>

Learn supplier functions with Supplier<T>.

The Supplier<T> interface

Supplier<T> is a factory function that takes no parameter and produces a T value. Its single abstract method is get. It is used to defer value production (lazy evaluation).

Example: Supplier<String> greeting = () -> "Hello";. Then greeting.get() returns "Hello". Supplier is ideal for an expensive value that should only be computed when needed; production does not happen until get is called.

Laziness with Supplier

The most powerful feature of Supplier is its laziness. Nothing is computed until get is called. This is the standard way to do expensive work only when truly needed.

Example: Supplier<List<String>> data = () -> loadFromDisk(). Here loadFromDisk runs only when data.get() is called. You see the same pattern in Optional.orElseGet and Stream.generate; both take a Supplier and produce values lazily.

Exercise Produce a value with Supplier

Define a Supplier<String> that uses the lambda () -> "Hello". Print the result of get() with System.out.println.

Show example solution

import java.util.function.Supplier;

public class SupplierExample {
    public static void main(String[] args) {
        Supplier<String> greeting = () -> "Hello";
        System.out.println(greeting.get());
    }
}

Test yourself

Complete the Supplier call

Supplier<String> greeting = () -> "Merhaba";
String result = greeting.____();

Show answer

Supplier<String> greeting = () -> "Merhaba";
String result = greeting.get();

Match the Supplier concepts

Supplier<T>

Produces a value
get

Call method
No parameter

Supplier's trait
T get()

Signature
Which interface returns a value without taking a parameter?
- Function<T,R>
- Consumer<T>
- Predicate<T>
- Supplier<T>
Show answer

Supplier<T> — Supplier<T> takes no parameter and returns T.

Next lesson: @FunctionalInterface

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