Try this
Window > Show View > Package Explorer
it will display the hidden 'Package Explorer' on your eclipse IDE.
• 'Window' is in your Eclipse' menubar.
For Eclipse version 4.3.0.v20130605-2000. You can use the Java (default) perspective. In this perspective, it provides the Package Explorer view.
To use the Java (default) perspective: Window -> Open Perspective -> Other... -> Java (default) -> Ok
If you already use the Java (default) perspective but accidentally close the Package Explorer view, you can open it by; Window -> Show View -> Package Explorer (Alt+Shift+Q,P)
If the Package Explorer still doesn't appear in the Java (default) perspective, I suggest you to right-click on the Java (default) perspective button that is located in the top-right of the Eclipse IDE and then select Reset. The Java (default) perspective will show the Package Explorer view, Code pane, Outline view, Problems, JavaDoc and Declaration View.
You might be in debug mode. If this is the problem, you can simply click on the "Java" button (next to the "Debug" button) in the upper-right hand corner, or click on "Open Perspective" and then select "Java (default)" from the "Open Perspective" window.
Try Window > Open Perspective > Java Browsing or some other Java perspectives
The simplest, and best long-term solution
Go to the main menu on top of Eclipse and locate Window next to Run and expand it.
Window->Reset Perspective... to restore all views to their defaults
It will reset the default setting.
Source: Stackoverflow.com