关于Java版本的困惑

Question

So I'm trying to get the latest version of Java. When I run:

java -version

I get:

java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)

When I run:

javac -version

I get:

javac 1.6.0_65

Now I've just downloaded and installed JDK 8. When I go into System Preferences --> Java --> Update, I see:

Your system has the recommended vesion of Java.

Java 8 Update 05.

I guess I have a few questions:

1) Don't I want the JDK and my version of Java to match up?

2) Why does my Java Control Panel claim I have Java 8, but my work in the terminal (when checking my Java version) says otherwise?

Thanks for the help, Mariogs

Answer 1

The Java Platform offers both the JRE and the JDK in order for users to run Java programs. The JRE stands for the Java Runtime Environment, and the JDK stands for the Java Development Kit.

The JDK is meant for Java developers - that is, those who build applications/write programs in Java. It contains tools that are needed for Java coding, including -javac to compile programs.

The JRE is meant for regular users - those who only need to run Java programs on their computer and are not interested in development.

The reason for the discrepancy in your case is because you're looking at the JRE and JDK and trying to compare the two. The current JDK that you have is Java 8 , whereas the current JRE that you have is 1.6.0_65 . It is problematic that your JRE version does not match your JDK version, but without your PATH variable or other information about your install, we can't help you fix your installation.

Answer 2

The probably "simple" answer is you have two versions of java installed. On the command line you currently use 1.6. Thus the old one is active. In system preferences you see the version of java 8.

Windows: You can change the version of the command line to java 8. Set PATH environment variable and JAVA_HOME or via windows preferences. I recommend the first one.

Mac: /usr/libexec/java_home is the starting point for switching java versions on the command line. Check out this post to understand how to handle different java versions on the Mac. IMHO this answer is a good solution.

Answer 3

1) Yes, if you use the JDK at all, you want the JRE (runtime environment) to come from the JDK (development environment) (a JDK necessarily includes a JRE).

2) Likely your path variable is set so that you invoke Java from your Java 6 installation; you need to find the equivalent for your Java 8 installation and set the path for that. Without information about your operating system, we can't help you do that.

Answer 4

Following are the things we should know

1. Our OS comes with predefined (built-in)set of tools and utilities. When we try to execute command eg cls in windows command line then it is already present in system path variable and os will refer the corresponding binary of cls to execute the command.

2. However, when we install any third party tool/software then path variable is not updated accordingly.

3. Eg When we install different versions of java on your system then installations goes to different directories. Eg for JDK:

     ==> C:\\Program Files\\Java\\jdk1.8.0_161 

and for JRE: ==> C:\\Program Files\\Java\\jre1.8.0_161

4. We need to update path variable of OS to point to appropriate directory. If we set path of JDK then it will execute binary from JDK bin directory.

Answer 5

Let me see if I can clear it up for you.

1)Yes, arguably you nearly want this to be true.

2)It could be few things, but most likely that a previous instillation was not properly removed. So one gets called instead of the other.