Welcome to the unit on Partial Application in Java! As we continue our journey through the Advanced Functional Programming Techniques course, this lesson will guide you through the concept of partial application. You'll learn how to create functions by fixing some arguments while leaving others to be specified later. This technique helps you write more modular, reusable, and maintainable code.

In this lesson, you will:

• Understand the concept of partial application in functional programming.
• Learn how to create partially applied functions in Java.
• Explore practical applications of partial application through concrete examples.

Partial application is a technique that allows you to transform a function with multiple parameters into a series of functions that each take fewer parameters. Here’s how it works by fixing one or more arguments in advance:

1. Simplification: By setting some arguments beforehand, you create specialized functions that take fewer parameters. This makes your functions easier to understand and use in different contexts since the complexity is reduced.

2. Reusability: Specialized functions derived from a general one can be used in multiple scenarios without rewriting the original function. This enhances code modularity and reduces redundancy in your programming tasks, leading to maintainable and cleaner code.

3. Flexibility: By breaking down functions into smaller, reusable pieces, partial application allows for greater flexibility in how functions are composed and reused. It promotes a more modular approach to building complex functionalities.

To better understand these benefits, let’s look at a concrete example.

Let’s say you have a function that adds two numbers:

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1BiFunction<Integer, Integer, Integer> add = (a, b) -> a + b;

Here, add is a BiFunction that takes two integers, a and b, and returns their sum. The function can be partially applied by fixing one of its arguments:

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1Function<Integer, Integer> addFive = partialApply(add, 5);

In this step, we use the partialApply method to create a new function addFive by fixing the first argument of the add function to 5. Now, addFive only requires a single argument to complete the addition.

When you apply the second argument:

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1int result = addFive.apply(10); // This will be 5 + 10 = 15

The addFive function takes 10 as its argument, adds it to the fixed value 5, and returns 15.

Finally, the partialApply method is defined as follows:

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1public static <A, B, C> Function<B, C> partialApply(BiFunction<A, B, C> func, A a) {
2    return (b) -> func.apply(a, b);
3}

This method takes a BiFunction and an argument a, returning a new Function that accepts the remaining argument b. The new function is more specific and requires fewer arguments, making it easier to work with in various contexts.

Now that you've explored the basics of partial application, it's time to see how this technique can simplify your coding tasks. Let's dive into the practice section and apply what you’ve learned!