Supplier: Data Generation

Here's how the Supplier functional interface is implemented:

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@FunctionalInterface
public interface Supplier<T> {
    T get();
}

The key responsibility of the get() method is to return an object of type T without taking any parameters.

Practical Use of Supplier

Supplier is often used in situations where data needs to be generated on demand. This can be useful for lazy initialization, generating random values, or retrieving values from an external source.

Let's create a system that generates random passwords. Using the Supplier functional interface, you can easily organize password generation on request.

You create a Supplier that generates a random password of 12 characters. The lambda expression inside the Supplier uses the Random class to select random characters from a string.

The get() method triggers this password generation logic only when needed, enabling lazy generation of values.

Lazy Generation

Initially, you create the Supplier, but the code inside it doesn't execute immediately. This is an important feature. Instead of executing some logic right away (e.g., generating a password), you simply record it inside the Supplier as an instruction to be executed later when required.

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Supplier<String> passwordSupplier = () -> {
    String characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()";
    StringBuilder password = new StringBuilder();
    Random random = new Random();
    for (int i = 0; i < 12; i++) {
        int index = random.nextInt(characters.length());
        password.append(characters.charAt(index));
    }
    return password.toString();
};

Here, the code inside the Supplier (password generation) doesn't execute immediately. Instead, you're saying, "When someone asks, this is how you'll generate the password." Now, when you call get() on this Supplier:

String generatedPassword = passwordSupplier.get();

Only then does the code inside the Supplier execute, and the password is generated. This is lazy execution.

Key Responsibilities