Class FallThroughCheck
- All Implemented Interfaces:
Configurable
,Contextualizable
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 isboolean
. Default value isfalse
. -
Property
reliefPattern
- Define the RegExp to match the relief comment that suppresses the warning about a fall through. Type isjava.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
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate boolean
Control whether the last case group must be checked.static final String
A key is pointing to the warning message text in "messages.properties" file.static final String
A key is pointing to the warning message text in "messages.properties" file.private Pattern
Define the RegExp to match the relief comment that suppresses the warning about a fall through. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprivate boolean
Checks if a given IF terminated by return, throw or, if allowed break, continue.private boolean
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
Checks if a given try/catch/finally block terminated by return, throw or, if allowed break, continue.int[]
The configurable token set.int[]
Returns the default token a check is interested in.int[]
The tokens that this check must be registered for.private boolean
hasFallThroughComment
(DetailAST currentCase, DetailAST nextCase) Determines if the fall through case betweencurrentCase
andnextCase
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
(Pattern pattern, 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
(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
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Field Details
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MSG_FALL_THROUGH
A key is pointing to the warning message text in "messages.properties" file.- See Also:
-
MSG_FALL_THROUGH_LAST
A key is pointing to the warning message text in "messages.properties" file.- See Also:
-
checkLastCaseGroup
private boolean checkLastCaseGroupControl whether the last case group must be checked. -
reliefPattern
Define the RegExp to match the relief comment that suppresses the warning about a fall through.
-
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Constructor Details
-
FallThroughCheck
public FallThroughCheck()
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Method Details
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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 classAbstractCheck
- 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 classAbstractCheck
- 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 classAbstractCheck
- Returns:
- the token set this check is designed for.
- See Also:
-
setReliefPattern
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
Description copied from class:AbstractCheck
Called to process a token.- Overrides:
visitToken
in classAbstractCheck
- Parameters:
ast
- the token to process
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isTerminated
Checks if a given subtree terminated by return, throw or, if allowed break, continue.- Parameters:
ast
- root of given subtreeuseBreak
- should we consider break as terminator.useContinue
- should we consider continue as terminator.- Returns:
- true if the subtree is terminated.
-
checkSlist
Checks if a given SLIST terminated by return, throw or, if allowed break, continue.- Parameters:
slistAst
- SLIST to checkuseBreak
- should we consider break as terminator.useContinue
- should we consider continue as terminator.- Returns:
- true if SLIST is terminated.
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checkIf
Checks if a given IF terminated by return, throw or, if allowed break, continue.- Parameters:
ast
- IF to checkuseBreak
- should we consider break as terminator.useContinue
- should we consider continue as terminator.- Returns:
- true if IF is terminated.
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checkLoop
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.
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checkTry
Checks if a given try/catch/finally block terminated by return, throw or, if allowed break, continue.- Parameters:
ast
- loop to checkuseBreak
- should we consider break as terminator.useContinue
- should we consider continue as terminator.- Returns:
- true if try/catch/finally block is terminated.
-
checkSwitch
Checks if a given switch terminated by return, throw or, if allowed break, continue.- Parameters:
literalSwitchAst
- loop to checkuseContinue
- should we consider continue as terminator.- Returns:
- true if switch is terminated.
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checkSynchronized
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.
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hasFallThroughComment
Determines if the fall through case betweencurrentCase
andnextCase
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
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matchesComment
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.
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