Question

Why does Eclipse take a fine grained approach when importing types? In C# I’m used to things like “using System.Windows.Controls” and being done with it, but Eclipse prefers to import each widget I reference individually (using the Ctrl+Shift+O shortcut). Is there any harm to importing an entire namespace if I know I’ll need multiple types in it?

Answer 1

The only harm that wildcard package imports can cause is an increased chance of namespace collisions if there are multiple classes of the same name in multiple packages.

Say for example, I want to program to use the ArrayList class of the Java Collections Framework in an AWT application that uses a List GUI component to display information. For the sake of an example, let’s suppose we have the following:

// 'ArrayList' from java.util
ArrayList<String> strings = new ArrayList<String>();

// ...

// 'List' from java.awt
List listComponent = new List()

Now, in order to use the above, there would have to be an import for those two classes, minimally:

import java.awt.List;
import java.util.ArrayList;

Now, if we were to use a wildcard in the package import, we’d have the following.

import java.awt.*;
import java.util.*;

However, now we will have a problem!

There is a java.awt.List class and a java.util.List, so referring to the List class would be ambiguous. One would have to refer to the List with a fully-qualified class name if we want to remove the ambiguity:

import java.awt.*;
import java.util.*;

ArrayList<String> strings = new ArrayList<String>();

// ...

// 'List' from java.awt -- need to use a fully-qualified class name.
java.awt.List listComponent = new java.awt.List()

Therefore, there are cases where using a wildcard package import can lead to problems.