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

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
private static class	UnusedImportsCheck.Frame Holds the names of referenced types and names of declared inner types.

Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

AutomaticBean.OutputStreamOptions

Field Summary

Fields

Modifier and Type	Field and Description
private static java.util.regex.Pattern	ARGUMENT_NAME Regex to match argument names.
private static java.util.regex.Pattern	CLASS_NAME Regex to match class names.
private boolean	collect Flag to indicate when time to start collecting references.
private UnusedImportsCheck.Frame	currentFrame The scope is being processed.
private static java.util.regex.Pattern	FIRST_CLASS_NAME Regex to match the first class name.
private java.util.Set<FullIdent>	imports Set of the imports.
private static java.util.regex.Pattern	JAVA_LANG_PACKAGE_PATTERN Regexp pattern to match java.lang package.
static java.lang.String	MSG_KEY A key is pointing to the warning message text in "messages.properties" file.
private boolean	processJavadoc Control whether to process Javadoc comments.
private static java.lang.String	STAR_IMPORT_SUFFIX Suffix for the star import.

Constructor Summary

Constructors

Constructor and Description
UnusedImportsCheck()

Method Summary

Modifier and Type	Method and Description
void	beginTree(DetailAST rootAST) Called before the starting to process a tree.
private void	collectReferencesFromJavadoc(DetailAST ast) Collects references made in Javadoc comments.
private static java.util.Set<java.lang.String>	collectReferencesFromJavadoc(TextBlock textBlock) Process a javadoc TextBlock and return the set of classes referenced within.
void	finishTree(DetailAST rootAST) Called after finished processing a tree.
int[]	getAcceptableTokens() The configurable token set.
int[]	getDefaultTokens() Returns the default token a check is interested in.
int[]	getRequiredTokens() The tokens that this check must be registered for.
private static java.util.List<JavadocTag>	getValidTags(TextBlock cmt, JavadocUtil.JavadocTagType tagType) Returns the list of valid tags found in a javadoc TextBlock.
private boolean	isUnusedImport(java.lang.String imprt) Checks whether an import is unused.
void	leaveToken(DetailAST ast) Called after all the child nodes have been process.
private static java.util.Set<java.lang.String>	matchPattern(java.lang.String identifier, java.util.regex.Pattern pattern) Extracts a list of texts matching a Pattern from a String.
private void	processIdent(DetailAST ast) Collects references made by IDENT.
private void	processImport(DetailAST ast) Collects the details of imports.
private static java.util.Set<java.lang.String>	processJavadocTag(JavadocTag tag) Returns a list of references found in a javadoc JavadocTag.
private void	processStaticImport(DetailAST ast) Collects the details of static imports.
void	setProcessJavadoc(boolean value) Setter to control whether to process Javadoc comments.
private static java.lang.String	topLevelType(java.lang.String type) If the given type string contains "." (e.g.
void	visitToken(DetailAST ast) Called to process a token.

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck

clearViolations, destroy, getFileContents, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, init, isCommentNodesRequired, log, log, log, setFileContents, setTabWidth, setTokens

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

finishLocalSetup, getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, setId, setSeverity

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

configure, contextualize, getConfiguration, setupChild

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MSG_KEY

public static final java.lang.String MSG_KEY

A key is pointing to the warning message text in "messages.properties" file.

See Also:

Constant Field Values

CLASS_NAME

private static final java.util.regex.Pattern CLASS_NAME

Regex to match class names.

FIRST_CLASS_NAME

private static final java.util.regex.Pattern FIRST_CLASS_NAME

Regex to match the first class name.

ARGUMENT_NAME

private static final java.util.regex.Pattern ARGUMENT_NAME

Regex to match argument names.

JAVA_LANG_PACKAGE_PATTERN

private static final java.util.regex.Pattern JAVA_LANG_PACKAGE_PATTERN

Regexp pattern to match java.lang package.

STAR_IMPORT_SUFFIX

private static final java.lang.String STAR_IMPORT_SUFFIX

Suffix for the star import.

See Also:

Constant Field Values

imports

private final java.util.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 Detail

UnusedImportsCheck

public UnusedImportsCheck()

Method Detail

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:

TokenTypes

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:

TokenTypes

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:

TokenTypes

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(java.lang.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 java.util.Set<java.lang.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 java.util.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 java.util.Set<java.lang.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 java.util.Set<java.lang.String> matchPattern(java.lang.String identifier,
                                                            java.util.regex.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 java.lang.String topLevelType(java.lang.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