If I install an older, deprecated Java runtime, will that mess up applications that use the current Java version? I own a really old version of Photoshop. After I upgraded to El Capitan when I attempt to launch Photoshop I get a dialog saying...


  To open "Adobe Photoshop CS5.1.app" you need to install the legacy Java SE 6 runtime.


This is my current system Java version that came with the OS -->

java -showversion
java version "1.8.0_65"
Java(TM) SE Runtime Environment (build 1.8.0_65-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.65-b01, mixed mode)


I downloaded the old, deprecated Java 6 DMG, but I haven't installed it yet.

My question is, will it replace the Apple's distributed Java?

And if so, is that likely to break applications that are expecting an up-to-date Java version?

Or will it just make the older JRE available as an alternative for applications that need it?
So long as you've downloaded the Java 6 installer from Apple it will work without affecting your current Java installation.