To open a Java file in the Java editor, double click on the file in the Package Explorer view.

Notice the syntax highlighting. Examples of parts of java source which are rendered differently are: Regular comments, Javadoc comments, Keywords, Strings:

Look at the Outline view. It displays an outline of the Java file including the package declaration, import declarations, fields, types and methods. The Outline view also indicates whether a Java element is static, abstract, final, etc. The outline view also shows you whether a method is overridden from a base class or when it implements a method from an interface.

Toggle the Hide Fields, Hide Static Members, and Hide Non-Public Members buttons in the Outline view toolbar to filter the view's display.

Toggle the Sort button in the Outline view to sort the Java elements in alphabetical order rather than in the order they appear in the Java file.

You can edit source code by viewing the whole Java file, or you can narrow the view to a single Java element. Click the Show Source of Selected Element Only button in the toolbar. Next, in the Outline view, select any element and note that only the selected element is displayed in the Java editor.

Press the Show Source of Selected Element Only button again to see the whole Java file again. In the Outline view, select different elements and note that they are once again displayed in a whole file view in the editor. The Outline view selection is now indicated with a range indicator on the vertical ruler on the left border of the Java editor.