Supplier Interface in Java with Examples

The Supplier<T> interface is a functional interface introduced in Java 8 and available in the java.util.function package. It represents a supplier of results that does not accept any input arguments but returns a value of a specified type.

• Represents a function with no input and one output.
• Useful for lazy value generation and object creation.
• Supports lambda expressions and method references.

import java.util.function.Supplier;

public class Main {
    public static void main(String[] args) {

        Supplier<String> message =
            () -> "Welcome to Java";

        System.out.println(message.get());
    }
}

Welcome to Java

Explanation: In this example, the Supplier does not take any input. When the get() method is called, it returns the string "Welcome to Java".

Syntax

@FunctionalInterface
public interface Supplier<T>

Here,

• T :Type of the result supplied by the function.

Method of Supplier Interface

1. get() Method

The get() method is the functional method of the Supplier interface. It generates and returns a value without taking any input parameters.

• Takes no arguments.
• Returns a value of type T.
• Commonly used for lazy initialization and object creation.

Syntax:

T get()

Return Value: Returns a value of type T

import java.util.function.Supplier;

public class Main{
    public static void main(String args[])
    {

        // This function returns a random value.
        Supplier<Double> randomValue = () -> Math.random();

        // Print the random value using get()
        System.out.println(randomValue.get());
    }
}

0.33157850608822403

Explanation: In this example, the Supplier generates a random double value whenever the get() method is called. Since no input is required, the value is produced directly by the supplier.

Example: Supplying an Object

import java.util.function.Supplier;

public class Main {
    public static void main(String[] args) {

        Supplier<StringBuilder> supplier =
            () -> new StringBuilder("Java");

        System.out.println(supplier.get());
    }
}

Java

Explanation: Here, the Supplier creates and returns a new StringBuilder object whenever get() is invoked.

Supplier vs Function

Advantages of Supplier Interface

• Does not require any input arguments.
• Useful for generating values on demand.
• Supports lazy initialization.
• Works seamlessly with lambda expressions.
• Reduces boilerplate code.
• Commonly used in streams, factories, and object creation patterns