10 - Methods in Java/003 Recursive methods_en.srt

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Hello team!

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In this lesson we will learn what are recursive methods and how to use them.

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What is recursion?

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Recursion is a process in which a method calls itself continuously.

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A method in Java that calls itself is called recursive method.

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Let's write the easiest recursive method.

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I have the method which calls itself, and when it calls itself, it calls the same method again.

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This is recursive method.

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What is wrong here?

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Let's run our program.

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We have stack overflow error.

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Why this has happened?

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Because when a recursive call is made, new storage locations for variables are located in the stack

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memory of the JVM.

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So each recursive call will add a new frame to the stack.

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That means we can run out of memory, because information about initial and other method invocations

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won't be removed from the stack.

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We need to finish method to release memory in stack.

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But when we call the same method again and again, it just can't be completed.

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So here is an important rule which you have to always keep in mind.

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When you create recursive methods, you should clearly define stop condition.

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The condition when recursion must be stopped and value should be returned.

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Let's find factorial of a number.

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Factorial of a positive integer is a result of multiplication Application of all positive integers less

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than or equal to original number.

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We'll write recursive method in case I is not equal to zero.

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Then we can multiply I by the result of the same method, but with number decreased by one, and when

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I will be equal to zero, we return one and no recursion here anymore.

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We broke the chain of recursion calls.

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Let me comment this method first.

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Now I can run the program again and you see the result in console.

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Here we calculated factorial of three and four.

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Now when you know how recursive method works, let's recap.

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Pros and cons of recursive methods.

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Recursive methods usually look clean and easy to understand.

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Often we can achieve our goal without recursive methods.

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For example, here is the same method to calculate factorial but without recursion, and you see that

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it is a bit longer and less clear than recursive one.

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So clean design is an advantage of recursive methods, but recursive methods have one huge drawback.

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In case there will be a lot of methods, invocations or stop condition will be written incorrectly.

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Your program will be stopped because of stack overflow error.

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Now you know pros and cons of recursive methods.

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I will share with you coding exercises to write recursive methods.

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Thanks a lot for your attention.

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See you in the next lesson.

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Your.