Eclipse: Change general project to Java project

1. Open your project file (which is located in your root directory of the appropriate project) called .project with your default editor.
2. Add <nature>org.eclipse.jdt.core.javanature</nature> tag in <natures>
3. Save the changed file.
4. Project automatically changed to java project.

Copying Eclipse Preferences

If you want to transfer your preferences from one Eclipse installation to another, you can try the following approaches:

Option 1: Export/Import
Export your current preferences to a file and then import them into your new installation.
Go to File > Export and then choose to export General > Preferences to the local filesystem. Then start your second version of Eclipse, go to File > Import and choose to import General > Preferences.

Option 2: Copy runtime setting directory
Copy ${ECLIPSE_WORKSPACE}/.metadata/.plugins/org.eclipse.core.runtime/.settings from the existing installation to the new one.