Class 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:
    • CLASS_NAME

      private static final Pattern CLASS_NAME
      Regex to match class names.
    • FIRST_CLASS_NAME

      private static final Pattern FIRST_CLASS_NAME
      Regex to match the first class name.
    • ARGUMENT_NAME

      private static final Pattern ARGUMENT_NAME
      Regex to match argument names.
    • JAVA_LANG_PACKAGE_PATTERN

      private static final Pattern JAVA_LANG_PACKAGE_PATTERN
      Regexp pattern to match java.lang package.
    • STAR_IMPORT_SUFFIX

      private static final String STAR_IMPORT_SUFFIX
      Suffix for the star import.
      See Also:
    • imports

      private final Set<FullIdent> imports
      Set of the imports.
    • collect

      private boolean collect
      Flag to indicate when time to start collecting references.
    • processJavadoc

      private boolean processJavadoc
      Control whether to process Javadoc comments.
    • currentFrame

      private UnusedImportsCheck.Frame currentFrame
      The scope is being processed. Types declared in a scope can shadow imported types.
  • 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
    • leaveToken

      public void leaveToken(DetailAST ast)
      Description copied from class: AbstractCheck
      Called after all the child nodes have been process.
      Overrides:
      leaveToken in class AbstractCheck
      Parameters:
      ast - the token leaving
    • isUnusedImport

      private boolean isUnusedImport(String imprt)
      Checks whether an import is unused.
      Parameters:
      imprt - an import.
      Returns:
      true if an import is unused.
    • processIdent

      private void processIdent(DetailAST ast)
      Collects references made by IDENT.
      Parameters:
      ast - the IDENT node to process
    • processImport

      private void processImport(DetailAST ast)
      Collects the details of imports.
      Parameters:
      ast - node containing the import details
    • processStaticImport

      private void processStaticImport(DetailAST ast)
      Collects the details of static imports.
      Parameters:
      ast - node containing the static import details
    • collectReferencesFromJavadoc

      private void collectReferencesFromJavadoc(DetailAST ast)
      Collects references made in Javadoc comments.
      Parameters:
      ast - node to inspect for Javadoc
    • collectReferencesFromJavadoc

      private static Set<String> collectReferencesFromJavadoc(TextBlock textBlock)
      Process a javadoc TextBlock and return the set of classes referenced within.
      Parameters:
      textBlock - The javadoc block to parse
      Returns:
      a set of classes referenced in the javadoc block
    • getValidTags

      private static List<JavadocTag> getValidTags(TextBlock cmt, JavadocUtil.JavadocTagType tagType)
      Returns the list of valid tags found in a javadoc TextBlock.
      Parameters:
      cmt - The javadoc block to parse
      tagType - The type of tags we're interested in
      Returns:
      the list of tags
    • processJavadocTag

      private static Set<String> processJavadocTag(JavadocTag tag)
      Returns a list of references found in a javadoc JavadocTag.
      Parameters:
      tag - The javadoc tag to parse
      Returns:
      A list of references found in this tag
    • matchPattern

      private static Set<String> matchPattern(String identifier, Pattern pattern)
      Extracts a list of texts matching a Pattern from a String.
      Parameters:
      identifier - The String to match the pattern against
      pattern - The Pattern used to extract the texts
      Returns:
      A list of texts which matched the pattern
    • topLevelType

      private static String topLevelType(String type)
      If the given type string contains "." (e.g. "Map.Entry"), returns the top level type (e.g. "Map"), as that is what must be imported for the type to resolve. Otherwise, returns the type as-is.
      Parameters:
      type - A possibly qualified type name
      Returns:
      The simple name of the top level type