In order to learn how to program in JAVA and start developing JAVA Application, you need to install JDK (JAVA Development Kit) on windows or linux or ubuntu or mac system.
Please select and download most recent version of JDK from oracle website depending on your Operating System.
Once donwload completes, run the auto-installing executable that unpack and install JDK on your system.
Update the PATH Variable (Optional):
Although it is optional, I recommended that you update the path variable on your system. It provides you more convinience if you want to run JAVA executables form any directory.
If you do not set classpath, you will have to provide full path everytime you want to run JAVA executable.
To set PATH variable permanently, you need to provide path to to bin directory on installed JDK. On windows platform, follow these steps to set PATH variable :
1. Go to Control Panel.
2. Clcik on System and Maintainace.
3. Click on System.
4. Click on Change Settings.
5. Clcik on Advanced tab.
6. Click on Environment Variable.
7. If PATH variable exist, you can edit it or create new one.
8. Variable name should be PATH and variable value must be path to bin directory. e.g., C:\Program Files\Java\jdk1.7.0\bin
Please make sure that PATH variable may have more than one path separated by ";". If you want to add new value, close the previous one with ;
9. Save it and restart your system.
10. Open command line and type JAVA and press enter. See if it runs successfully.