Checks for imports

The property checkstyle.ignore.imports controls whether to check import statements. The property type is boolean and defaults to false.

Unused imports

Checkstyle uses a simple but very reliable algorithm to report on unused import statements. An import statement is considered unused if:

It is not referenced in the file. The algorithm does not support wild-card imports like import java.io.*;. Most IDE's provide very sophisticated checks for imports that handle wild-card imports.
It is a duplicate of another import. This is when a class is imported more than once.
The class imported is from the java.lang package. For example importing java.lang.String.
The class imported is from the same package.

Illegal imports

The property checkstyle.illegal.imports contains the set of import illegal package prefixes for import statements. The property type is string set and defaults to sun since programs that contain direct calls to the sun.* packages are not 100% Pure Java.