**`Function`** is a functional interface that accepts one argument and returns a result. The **`apply()` method** of the interface is the functional method.

The `Function` interface is defined in the `java.util.function` package. To import the `Function` interface, check the following import statement:
```
import java.util.function.Function;
```

# 
#  Syntax

---

```java
R apply(T t);
```

---

# 
## Parameters 

- **`T t`**: This is the function argument.


##
## Return value

The method returns the function result.

## Code

import java.util.function.Function;

public class Main {
    
    public static void main(String[] args){
        Function<Integer, Integer> addFunction = arg -> arg + 5;
        int arg = 1;
        System.out.println("Result of apply() on addFunction --> " + addFunction.apply(arg));
    }
}

# 
## Explanation

- **Line 1**: We import the `Function` interface from the `function` package.
- **Line 6**: We define an implementation of the `Function` interface called `addFunction`. `addFunction` accepts an integer and returns the result of adding `5` to the given integer.
- **Line 7**: We define an integer called `arg`.
- **Line 8**: We print the result of using the `apply()` method and pass `arg` as an argument.

What is the Function functional interface in Java?

Function is a Java functional interface that takes one argument and returns a result using the `apply()` method.