Update 103-functions.md (#1810)

* Update 103-functions.md

Added the content to learn Methods/Functions in Java.
Kindly merge this into the main branch!
Thank You!

* Update content/roadmaps/110-java/content/100-java-fundamentals/103-functions.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/110-java/content/100-java-fundamentals/103-functions.md

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 # Functions
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+A method/function is a way to perform some task. Similarly, in programming like Java, a function method is a block of code written to perform a specific task repeatedly. It provides reusability of code. We write the function once and use it many times. It works on the 'DRY' principle i.e., "Do not repeat yourself".
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+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
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+<BadgeLink badgeText='Read' href='https://www.javatpoint.com/method-in-java'>Methods/Functions in Java.</BadgeLink>
+<BadgeLink badgeText='Read' href='https://www.geeksforgeeks.org/methods-in-java/'>What are methods or functions in Java.</BadgeLink>
+<BadgeLink badgeText='Read' href='https://www.w3schools.com/java/java_methods.asp'>Learn Functions/Methods in Java</BadgeLink>
+<BadgeLink badgeText='Watch' href='https://www.youtube.com/watch?v=vvanI8NRlSI'>Functions / Methods in Java</BadgeLink>