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Learn how to effectively use method reference notation in Java to pass methods as parameters, creating modular and flexible code.
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How to Pass Methods as Parameters in Java Using Method Reference Notation

In Java, one powerful feature is the ability to pass methods as parameters using method reference notation. This ability allows for cleaner, more modular code, and can help in various programming scenarios. However, implementing this can sometimes lead to confusion or compilation errors. In this guide, we will explore how to create a utility class that accepts a class reference and a method to invoke, using method references effectively.

The Problem

Consider a situation where you have a utility class, Utils, that is supposed to execute a method of a specified domain class instance. Your goal is to make Utils generic enough so that it can execute various methods of different classes using method references.

To illustrate, let's say we have a domain class called DomainClass.

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You want to create a method in the Utils class that looks something like this:

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However, you're facing some challenges:

Compilation Issues: You need to find the right way to pass parameters to the execute method.

Scope of Method Execution: You need a way to invoke the method within the context of the domain class instance.

The Solution

To solve the issues above, we need to adjust our Utils class so that it can accept the right types and execute the method properly.

Step 1: Adjust the Execute Method

Instead of using Runnable, which does not provide an instance context, we should use a functional interface that can accept an instance of the domain class. The Consumer interface is perfect for this purpose. Here's how to define the execute method generically:

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Step 2: Calling the Execute Method

Now that we have our Utils.execute method set up correctly, you can easily call it with the desired method reference:

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Explanation of the Code

Generic Method: The execute method uses generics (<T>) to allow for any type of class passed to it.

Creating Instance: We create an instance of T using reflection with clazz.getConstructor().newInstance().

Executing the Reference Method: The method reference (DomainClass::dummyMethod) is called in the context of the created instance (objInstance) using referenceMethod.accept(objInstance).

Conclusion

By modifying the Utils class to accept a Consumer<T>, you can seamlessly pass methods as parameters using method reference notation. This approach not only resolves the compilation issues but also allows for calling methods in the right context. With these steps, you can write more flexible and modular code in Java, leveraging the power of method references.

Happy coding!