Some of my mac java programs won't open/work

Question

When I type " java -version " into the terminal it says :

 "Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
  Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)"

But when I open my system preferences and try to click on Java is says:

 "“Java” can’t be opened because it isn’t available." 

I don't know what that means but the real problem is that when I try to run/open some .jar files a pop-up comes up saying that this java file can't be opened check the console.

Why is this happening?

Answer 1

Looks like java is not installed on your machine.

From the docs , you can check if java is installed, the following way:

Mac OS X 10.6 and below: Apple's Java comes pre-installed with your Mac OS.

Mac OS X 10.7 (Lion) and above: Java is not pre-installed with Mac OS X versions 10.7 and above. To get the latest Java from Oracle, you will need Mac OS X 10.7.3 and above. If you have Java 7 or later versions, you will see a Java icon under System Preferences . Java versions 6 and below are listed in the Java Preferences.app located in the Applications > Utilities folder on your Mac.

You can find the java installation instruction for Mac here .