How come Java doesn't need 'prototype' like JS does?

[Stefan Jankovic]

I understand every major OOP principle in Java, so I thought that learning JS would be piece of cake. But then I came across term called prototype in JS which troubles me. Can someone tell me how Java doesn't need prototypes unlike JS? What are prototypes replaced by in Java and how can I picture it from Java's perspective so I can understand it better in JS?

[Campbell Ritchie]

You wouldn't use English skills as a guide to learning Japanese, You would learn Japanese anew. Similarly, forget all about Java® when learning JS; the similarlity between the names is misleading.
Even the name JS is not quite correct; nobody ever uses the correct name for the language, which is ECMAScript. You haven't heard that name because nobody says ECMAScript.

[Jeanne Boyarsky]

Java has type safety and doesn't let you add methods at runtime so prototype doesn't apply. You aren't going to be able to understand it from a Java perspective.

[Bear Bibeault]

JavaScript's prototype is its means to effect inheritance. Java has classes. It's like asking why a steam engine doesn't need gasoline - different mechanisms to achieve a similar goal.
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"But wait!" you say "JavaScript now has classes!" Well, sort of -- it's all just syntactic sugar on top of the `prototype` mechanisms.

[Bear Bibeault]

And to Campbell's point: yes, knowing Java is a detriment towards learning JavaScript properly -- especially modern JS.

[Campbell Ritchie]

Bear Bibeault wrote:. . . why a steam engine doesn't need gasoline . . .

Nice to see you again, Bear
Nice analogy. Can I be naughty and change it to, “why a steam engine doesn't have spark plugs.” Or even, “why a petrol (=gasoline) engine doesn't have a boiler.”