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2 minute read - FAQ IntelliJ Java For Testers

How to Diff Java Code in IntelliJ - 3 ways to use the Compare Tool

Oct 12, 2017

TL;DR IntelliJ has an inbuilt diff tool which you can use to compare files, classes or code with the clipboard. Just right click and choose Compare.

I was busy refactoring code in RestMud this morning because I want to try and open source the basic game engine, and then later the Web/REST API, but I want to tidy up the code a little first.

I’ve been working through the code:

  • moving classes into new packages
  • splitting classes to make code clearer and easier to manage
  • new classes make code easier to test

And the more I tidy it up in general, the easier it is to spot smaller problems of code duplication.

Sometimes I fix the duplication by:

  • extracting code into a new class and delegating functionality off to the class
  • extracting code into private methods

IntelliJ has an incredibly useful piece functionality to help with that in the form of the Compare Tool.

The Compare tool

The compare tool is a built in Diff tool.

I can use it in three different ways:

  • right click on a file and “Compare” then choose a file on my hard drive to compare with
  • select two classes in the project view and right click to “Compare”
  • select code, add it into the clipboard, then highlight a different block of code and “Compare with Clipboard”

They all use the same ‘diff’ view and this is much easier than:

  • using a separate tool like WinMerge to compare files outside of the IDE.
  • splitting the window and visually trying to compare code

I show all three approaches in this short YouTube Video.