com.puppycrawl.tools.checkstyle.checks.coding

Class FallThroughCheck

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.coding.FallThroughCheck

All Implemented Interfaces:

Configurable, Contextualizable

public class FallThroughCheck
extends AbstractCheck

Checks for fall-through in switch statements. Finds locations where a case contains Java code but lacks a break, return, throw or continue statement.

The check honors special comments to suppress the warning. By default the texts "fallthru", "fall thru", "fall-thru", "fallthrough", "fall through", "fall-through" "fallsthrough", "falls through", "falls-through" (case sensitive). The comment containing these words must be all on one line, and must be on the last non-empty line before the case triggering the warning or on the same line before the case(ugly, but possible).

Note: The check assumes that there is no unreachable code in the case.

• Property checkLastCaseGroup - Control whether the last case group must be checked. Type is boolean. Default value is false.
• Property reliefPattern - Define the RegExp to match the relief comment that suppresses the warning about a fall through. Type is java.util.regex.Pattern. Default value is "falls?[ -]?thr(u|ough)".

To configure the check:

 <module name="FallThrough"/>
 

Example:

 public void foo() throws Exception {
   int i = 0;
   while (i >= 0) {
     switch (i) {
       case 1:
         i++;
       case 2: // violation, previous case contains code but lacks
               // break, return, throw or continue statement
         i++;
         break;
       case 3: // OK
         i++;
         return;
       case 4: // OK
         i++;
         throw new Exception();
       case 5: // OK
         i++;
         continue;
       case 6: // OK
       case 7: // Previous case: OK, case does not contain code
               // This case: OK, by default the last case might not have statement
               // that transfer control
         i++;
     }
   }
 }
 

Example how to suppress violations by comment:

 switch (i) {
   case 1:
     i++; // fall through

   case 2: // OK
     i++;
     // fallthru
   case 3: { // OK
     i++;
   }
   /* fall-thru */
   case 4: // OK
     i++;
     // Fallthru
   case 5: // violation, "Fallthru" in case 4 should be "fallthru"
     i++;
     // fall through
     i++;
   case 6: // violation, the comment must be on the last non-empty line before 'case'
     i++;
   /* fall through */case 7: // OK, comment can appear on the same line but before 'case'
     i++;
 }
 

To configure the check to enable check for last case group:

 <module name="FallThrough">
    <property name="checkLastCaseGroup" value="true"/>
 </module>
 

Example:

 switch (i) {
   case 1:
     break;
   case 2: // Previous case: OK
           // This case: violation, last case must have statement that transfer control
     i++;
 }
 

To configure the check with custom relief pattern:

 <module name="FallThrough">
    <property name="reliefPattern" value="FALL?[ -]?THROUGH"/>
 </module>
 

Example:

 switch (i) {
   case 1:
     i++;
     // FALL-THROUGH
   case 2: // OK, "FALL-THROUGH" matches the regular expression "FALL?[ -]?THROUGH"
     i++;
     // fall-through
   case 3: // violation, "fall-through" doesn't match
     break;
 }
 

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

• fall.through
• fall.through.last

Since:

3.4

Nested Class Summary

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

AutomaticBean.OutputStreamOptions

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	checkLastCaseGroup Control whether the last case group must be checked.
static java.lang.String	MSG_FALL_THROUGH A key is pointing to the warning message text in "messages.properties" file.
static java.lang.String	MSG_FALL_THROUGH_LAST A key is pointing to the warning message text in "messages.properties" file.
private java.util.regex.Pattern	reliefPattern Define the RegExp to match the relief comment that suppresses the warning about a fall through.

Constructor Summary

Constructors

Constructor and Description
FallThroughCheck()

Method Summary

Modifier and Type	Method and Description
private boolean	checkIf(DetailAST ast, boolean useBreak, boolean useContinue) Checks if a given IF terminated by return, throw or, if allowed break, continue.
private boolean	checkLoop(DetailAST ast) Checks if a given loop terminated by return, throw or, if allowed break, continue.
private boolean	checkSlist(DetailAST slistAst, boolean useBreak, boolean useContinue) Checks if a given SLIST terminated by return, throw or, if allowed break, continue.
private boolean	checkSwitch(DetailAST literalSwitchAst, boolean useContinue) Checks if a given switch terminated by return, throw or, if allowed break, continue.
private boolean	checkSynchronized(DetailAST synchronizedAst, boolean useBreak, boolean useContinue) Checks if a given synchronized block terminated by return, throw or, if allowed break, continue.
private boolean	checkTry(DetailAST ast, boolean useBreak, boolean useContinue) Checks if a given try/catch/finally block terminated by return, throw or, if allowed break, continue.
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 boolean	hasFallThroughComment(DetailAST currentCase, DetailAST nextCase) Determines if the fall through case between currentCase and nextCase is relieved by a appropriate comment.
private boolean	isTerminated(DetailAST ast, boolean useBreak, boolean useContinue) Checks if a given subtree terminated by return, throw or, if allowed break, continue.
private boolean	matchesComment(java.util.regex.Pattern pattern, java.lang.String line, int lineNo) Does a regular expression match on the given line and checks that a possible match is within a comment.
void	setCheckLastCaseGroup(boolean value) Setter to control whether the last case group must be checked.
void	setReliefPattern(java.util.regex.Pattern pattern) Setter to define the RegExp to match the relief comment that suppresses the warning about a fall through.
void	visitToken(DetailAST ast) Called to process a token.

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

beginTree, clearViolations, destroy, finishTree, getFileContents, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, init, isCommentNodesRequired, leaveToken, 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_FALL_THROUGH

public static final java.lang.String MSG_FALL_THROUGH

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

See Also:

Constant Field Values

MSG_FALL_THROUGH_LAST

public static final java.lang.String MSG_FALL_THROUGH_LAST

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

See Also:

Constant Field Values

checkLastCaseGroup

private boolean checkLastCaseGroup

Control whether the last case group must be checked.

reliefPattern

private java.util.regex.Pattern reliefPattern

Define the RegExp to match the relief comment that suppresses the warning about a fall through.

Constructor Detail

FallThroughCheck

public FallThroughCheck()

Method Detail

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

setReliefPattern

public void setReliefPattern(java.util.regex.Pattern pattern)

Setter to define the RegExp to match the relief comment that suppresses the warning about a fall through.

Parameters:

pattern - The regular expression pattern.

setCheckLastCaseGroup

public void setCheckLastCaseGroup(boolean value)

Setter to control whether the last case group must be checked.

Parameters:

value - new value of the property.

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

isTerminated

private boolean isTerminated(DetailAST ast,
                             boolean useBreak,
                             boolean useContinue)

Checks if a given subtree terminated by return, throw or, if allowed break, continue.

Parameters:

ast - root of given subtree

useBreak - should we consider break as terminator.

useContinue - should we consider continue as terminator.

Returns:

true if the subtree is terminated.

checkSlist

private boolean checkSlist(DetailAST slistAst,
                           boolean useBreak,
                           boolean useContinue)

Checks if a given SLIST terminated by return, throw or, if allowed break, continue.

Parameters:

slistAst - SLIST to check

useBreak - should we consider break as terminator.

useContinue - should we consider continue as terminator.

Returns:

true if SLIST is terminated.

checkIf

private boolean checkIf(DetailAST ast,
                        boolean useBreak,
                        boolean useContinue)

Checks if a given IF terminated by return, throw or, if allowed break, continue.

Parameters:

ast - IF to check

useBreak - should we consider break as terminator.

useContinue - should we consider continue as terminator.

Returns:

true if IF is terminated.

checkLoop

private boolean checkLoop(DetailAST ast)

Checks if a given loop terminated by return, throw or, if allowed break, continue.

Parameters:

ast - loop to check

Returns:

true if loop is terminated.

checkTry

private boolean checkTry(DetailAST ast,
                         boolean useBreak,
                         boolean useContinue)

Checks if a given try/catch/finally block terminated by return, throw or, if allowed break, continue.

Parameters:

ast - loop to check

useBreak - should we consider break as terminator.

useContinue - should we consider continue as terminator.

Returns:

true if try/catch/finally block is terminated.

checkSwitch

private boolean checkSwitch(DetailAST literalSwitchAst,
                            boolean useContinue)

Checks if a given switch terminated by return, throw or, if allowed break, continue.

Parameters:

literalSwitchAst - loop to check

useContinue - should we consider continue as terminator.

Returns:

true if switch is terminated.

checkSynchronized

private boolean checkSynchronized(DetailAST synchronizedAst,
                                  boolean useBreak,
                                  boolean useContinue)

Checks if a given synchronized block terminated by return, throw or, if allowed break, continue.

Parameters:

synchronizedAst - synchronized block to check.

useBreak - should we consider break as terminator.

useContinue - should we consider continue as terminator.

Returns:

true if synchronized block is terminated.

hasFallThroughComment

private boolean hasFallThroughComment(DetailAST currentCase,
                                      DetailAST nextCase)

Determines if the fall through case between currentCase and nextCase is relieved by a appropriate comment.

Parameters:

currentCase - AST of the case that falls through to the next case.

nextCase - AST of the next case.

Returns:

True if a relief comment was found

matchesComment

private boolean matchesComment(java.util.regex.Pattern pattern,
                               java.lang.String line,
                               int lineNo)

Does a regular expression match on the given line and checks that a possible match is within a comment.

Parameters:

pattern - The regular expression pattern to use.

line - The line of test to do the match on.

lineNo - The line number in the file.

Returns:

True if a match was found inside a comment.