How to Use Method References with Parameters in Java?

What are method references with parameters in Java and how can they be utilized?

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");

// Method reference to instance method
names.forEach(System.out::println);

Method references in Java are a shorthand notation of a lambda expression to call a method. They provide a clear and concise way to express a lambda when it references an existing method. You can use method references to refer to static methods, instance methods, or constructors. When parameters are involved, method references must match the functional interface's method signature they are targeting.

// Example of method reference with parameters

// Functional Interface
@FunctionalInterface
interface Printer {
    void print(String message);
}

public class MethodReferenceExample {
    public static void main(String[] args) {
        Printer printer = System.out::println; // Instance method reference
        printer.print("Hello, World!");
    }
}

Causes

• Using method references where lambda expressions should suffice.
• Misunderstanding what type of method reference to use (static vs instance).
• Passing the wrong number or type of parameters. Their types must match the target method.

Solutions

• Ensure you are using the correct type of method reference based on your context: static or instance.
• Verify that the functional interface to which you are passing the method reference accepts the method signature used in your reference.
• Consider providing a lambda expression as an alternative if the signature does not align.

Mistake: Not matching the parameters of the method reference with those defined in the functional interface.

Solution: Always check that the method reference's parameters align with the functional interface's method signature.

Mistake: Using a static method reference incorrectly where an instance method is required.

Solution: Ensure you understand when to use static versus instance method references; choose accordingly.