当我下载JDK时，预装的JRE会怎样？

Question

I am just interested, as far as I know if you want do some Java programming, you will need to download a JDK. As part of the JDK, it comes with the JRE. However, I think most Windows OS has pre-installed JRE already. I have several questions:

1. Does this mean this pre-installed version will get overwritten by the freshly downloaded and installed JRE?

2. Does a JRE have a version eg JRE-7,JRE-8?

3. If there is version for the JRE and the pre-installed JRE gets overwritten, does that mean there is a risk that some old applications will not work anymore?

Answer 1

1) This depends on your installation directory choice.

2) JRE is just a runtime part of the JDK (no compilers and tools) and thus is has the same versioning scheme as JDK.

3) Java is developed in the way that guarantees backwards compatibility. However you can get incompatibility problems with tools like Maven or libraries like JAXB.

Answer 2

Go to the Windows control panel, click Java , click the Java tab and then View. You will see all of the versions of Java that have been installed.