Configuring Java Environment JRE/ JDK in Eclipse

Devoid of what version of JDK you install on your machine, Eclipse comes with a JDK and it uses it unless we configure it manually to use a different one. We can simply direct Eclipse by specifying -vm option in the  eclipse.ini file which you can find in the directory where you unzip the downloaded eclipse zip file. There are different ways of specifying the -vm option depending on the operating system, which are described in detail here. The following worked for me on windows. Specify the option at the top of the file.

-vm

C:/Program Files (x86)/Java/jdk1.7.0_51/jre/bin/client/jvm.dll

Alternately we can install different versions of JREs on Eclipse manually as follow:

Click Eclipse menu named Window -> select menu option Preferences, the following window pops up.

Select Java from the left panel and click on Installed JREs. We can select one the JREs by checking the checkbox, add more versions of JREs which are available for selection while creating a new project.

Different versions of Eclipse support different versions of Java Development. In order to find out which versions of Java does an Eclipse version supports. Click the Compiler from the left panel from the above window. We can see a drop down list with all Java versions that Eclipse version supports. 

We may have to update or install patches in order to make Eclipse support later versions of Java Development. For example, Eclipse Kepler supports Java 7 by default, if we need Java 8 support in Kepler, we have to install this patch.

In certain scenarios, we may want to change an existing  project to a different version of Java. We may do that as follows:

Right click on the Project from Project Explorer, Click Properties, the following window pops up. Click Java Compiler from the left panel. There we can change the Compiler Compliance Level. We may have to build the project when ever we change the JDK/ JRE.

Next in order the update the JRE/ JDK associated with the project, we have to manually edit it from the project BuildPath as follows:

Right Click on Project from the Package Explorer, select BuildPath, then select Configure BuildPath from the sub menu. The following Properties window pops up. 

Select Libraries tab. You should see a version of JRE System Library. Select that and click Remove and then click on Add Library. The following window pops up. Select JRE System Library.

You will have 3 options to select the desired JRE library. Select a JRE/ JDK and click Finish. You should see the relevant JRE/ JDK added to your project BuildPath.