Package com.puppycrawl.tools.checkstyle.checks.imports

Class UnusedImportsCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.api.AutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.puppycrawl.tools.checkstyle.checks.imports.UnusedImportsCheck
All Implemented Interfaces:
Configurable, Contextualizable
public class UnusedImportsCheck extends AbstractCheck

Checks for unused import statements. 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.
  • Optionally: it is referenced in Javadoc comments. This check is on by default, but it is considered bad practice to introduce a compile time dependency for documentation purposes only. As an example, the import java.util.List would be considered referenced with the Javadoc comment {@link List}. The alternative to avoid introducing a compile time dependency would be to write the Javadoc comment as {@link java.util.List}.

The main limitation of this check is handling the case where an imported type has the same name as a declaration, such as a member variable.

For example, in the following case the import java.awt.Component will not be flagged as unused: 

 import java.awt.Component;
 class FooBar {
   private Object Component; // a bad practice in my opinion
   ...
 }
  • Property processJavadoc - Control whether to process Javadoc comments. Type is boolean. Default value is true.

To configure the check: 

 <module name="UnusedImports"/>

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • import.unused
Since:
3.0

  • Field Details

    • MSG_KEY

      public static final String MSG_KEY
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

  • Constructor Details

    • UnusedImportsCheck

      public UnusedImportsCheck()

  • Method Details

    • setProcessJavadoc

      public void setProcessJavadoc(boolean value)
      Setter to control whether to process Javadoc comments.
      Parameters:
      value - Flag for processing Javadoc comments.

    • beginTree

      public void beginTree(DetailAST rootAST)
      Description copied from class: AbstractCheck
      Called before the starting to process a tree. Ideal place to initialize information that is to be collected whilst processing a tree.
      Overrides:
      beginTree in class AbstractCheck
      Parameters:
      rootAST - the root of the tree

    • finishTree

      public void finishTree(DetailAST rootAST)
      Description copied from class: AbstractCheck
      Called after finished processing a tree. Ideal place to report on information collected whilst processing a tree.
      Overrides:
      finishTree in class AbstractCheck
      Parameters:
      rootAST - the root of the tree

    • getDefaultTokens

      public int[] getDefaultTokens()
      Description copied from class: AbstractCheck
      Returns the default token a check is interested in. Only used if the configuration for a check does not define the tokens.
      Specified by:
      getDefaultTokens in class AbstractCheck
      Returns:
      the default tokens
      See Also:

    • getRequiredTokens

      public int[] getRequiredTokens()
      Description copied from class: AbstractCheck
      The tokens that this check must be registered for.
      Specified by:
      getRequiredTokens in class AbstractCheck
      Returns:
      the token set this must be registered for.
      See Also:

    • getAcceptableTokens

      public int[] getAcceptableTokens()
      Description copied from class: AbstractCheck
      The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.
      Specified by:
      getAcceptableTokens in class AbstractCheck
      Returns:
      the token set this check is designed for.
      See Also:

    • visitToken

      public void visitToken(DetailAST ast)
      Description copied from class: AbstractCheck
      Called to process a token.
      Overrides:
      visitToken in class AbstractCheck
      Parameters:
      ast - the token to process