Tail recursion is a programming method where a method calls itself and immediately returns the value of that second call. It requires the called method to return a concrete value and can be found within control structures. Recursion is useful for repetitive tasks, such as calculating factorials.
Tail recursion is a type of programming method call in which one method calls itself, then immediately returns the value of that second call. In other words, tail recursion occurs when the final statement within a method is another call to the same method. The parameters in the second method call are usually different from those in the first, but this is not required. For this recursion to work, the method called within itself must return a concrete value, such as a number, string, or other object. Void methods, which don’t return a value, don’t work well for recursion.
The requirement that a recursive call be the last statement in its calling method does not necessarily mean that the recursive call is the last line in the method. A proper tail recursion call can also be found within a control structure, which means that, in source code, the control structure can terminate the method rather than the call. The important distinction here is that a control structure is not a programming instruction, but a built-in part of the computer language.
Tail recursion exists in many computer languages, including Java and C++. Often, these recursive calls can be rewritten using other means, such as for loops, while loops, or goto statements. The utility of recursion is found when making many sequential calls to the same method. Recursion is often the simplest and cleanest way to do repetitive tasks.
A common example of tail recursion is a method that calculates the factorial of a number. This process is ideal because starting with any number, every number before it is multiplied together. So, to find the factorial of 5, the correct process for doing this would be to multiply 5*4*3*2*1. The recursion occurs because of how the factorial method is structured: if the factorial is 1, it returns 1, otherwise it returns the factorial of the number given to the method minus one. This method is also useful because it can be written equivalently using either type of tail recursion, with or without a control statement around a final method call.
Tail recursion is just one example of the many types of recursion. The concept in all types of recursion is essentially the same, that somehow a method calls itself. Of these types, the distinction of tail recursion is that the value of a recursive call is returned immediately and nothing else happens in the calling method after that call.
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