Description

A fully qualified type reference, such as java.util.Map, is reported as unnecessary unless another type with the same simple name is also used in the file. For example, java.util.Map is allowed only when a different Map (e.g. com.example.Map, a locally declared Map, or a same-package or java.lang Map) is also referenced, since in that case qualification is required to tell the two types apart.

Using fully qualified names where they are not needed reduces readability and is inconsistent with common Java style conventions, which favor importing the type instead.

The following limitations apply:

• To distinguish a package qualified type (such as java.util.Map) from a reference to a nested type (such as Map.Entry), the check relies on the common convention that package names start with a lowercase letter. A qualified reference is treated as fully qualified only when the identifier preceding the simple name starts with a lowercase letter.
• References to nested types via an enclosing type (for example java.util.Map.Entry) and fully qualified annotations (for example @java.lang.Override) are not reported.
• On-demand (wildcard) imports, such as import java.util.*;, are checked against classes reachable on this check's own class loader. This reliably detects collisions from JDK packages (for example a fully qualified reference to a third-party Observer type being left alone because import java.util.*; also brings a different java.util.Observer into scope), but on-demand imports of third-party or project-local packages cannot be resolved this way and may still be flagged incorrectly.

Examples

To configure the check:

<module name="Checker">
  <module name="TreeWalker">
    <module name="UnnecessaryFullyQualifiedType"/>
  </module>
</module>

Example:

import java.util.HashMap;
import java.util.Map;

class Example1 {

  // violation below 'Unnecessary fully qualified type - java.util.List.'
  java.util.List<String> list;

  Map<Boolean, String> choiceMap = new HashMap<>();

  private java.sql.Date sqlDate; // ok as two different 'Date' declared

  private java.util.Date utilDate; // ok as two different 'Date' declared

}

Example of Usage

• Checkstyle Style

Violation Messages

• unnecessary.fully.qualified.type

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Fully Qualified Name

com.puppycrawl.tools.checkstyle.checks.imports.UnnecessaryFullyQualifiedTypeCheck

Use this fully qualified class name in configuration when an exact class reference is required.

Parent Module

TreeWalker