Package com.puppycrawl.tools.checkstyle.checks.coding

Class OneStatementPerLineCheck

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.OneStatementPerLineCheck
All Implemented Interfaces:
Configurable, Contextualizable
public final class OneStatementPerLineCheck extends AbstractCheck

Checks that there is only one statement per line.

Rationale: It's very difficult to read multiple statements on one line.

In the Java programming language, statements are the fundamental unit of execution. All statements except blocks are terminated by a semicolon. Blocks are denoted by open and close curly braces.

OneStatementPerLineCheck checks the following types of statements: variable declaration statements, empty statements, import statements, assignment statements, expression statements, increment statements, object creation statements, 'for loop' statements, 'break' statements, 'continue' statements, 'return' statements, resources statements (optional).

  • Property treatTryResourcesAsStatement - Enable resources processing. Type is boolean. Default value is false.

To configure the check: 

 <module name="OneStatementPerLine"/>

The following examples will be flagged as a violation: 

 //Each line causes violation:
 int var1; int var2;
 var1 = 1; var2 = 2;
 int var1 = 1; int var2 = 2;
 var1++; var2++;
 Object obj1 = new Object(); Object obj2 = new Object();
 import java.io.EOFException; import java.io.BufferedReader;
 ;; //two empty statements on the same line.

 //Multi-line statements:
 int var1 = 1
 ; var2 = 2; //violation here
 int o = 1, p = 2,
 r = 5; int t; //violation here

An example of how to configure the check to treat resources in a try statement as statements to require them on their own line: 

 <module name="OneStatementPerLine">
   <property name="treatTryResourcesAsStatement" value="true"/>
 </module>

Note: resource declarations can contain variable definitions and variable references (from java9). When property "treatTryResourcesAsStatement" is enabled, this check is only applied to variable definitions. If there are one or more variable references and one variable definition on the same line in resources declaration, there is no violation. The following examples will illustrate difference: 

 OutputStream s1 = new PipedOutputStream();
 OutputStream s2 = new PipedOutputStream();
 // only one statement(variable definition) with two variable references
 try (s1; s2; OutputStream s3 = new PipedOutputStream();) // OK
 {}
 // two statements with variable definitions
 try (Reader r = new PipedReader(); s2; Reader s3 = new PipedReader() // violation
 ) {}

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • multiple.statements.line
Since:
5.3

  • 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:

    • countOfSemiInLambda

      private final Deque<Integer> countOfSemiInLambda
      Counts number of semicolons in nested lambdas.

    • lastStatementEnd

      private int lastStatementEnd
      Hold the line-number where the last statement ended.

    • forStatementEnd

      private int forStatementEnd
      Hold the line-number where the last 'for-loop' statement ended.

    • inForHeader

      private boolean inForHeader
      The for-header usually has 3 statements on one line, but THIS IS OK.

    • isInLambda

      private boolean isInLambda
      Holds if current token is inside lambda.

    • lambdaStatementEnd

      private int lambdaStatementEnd
      Hold the line-number where the last lambda statement ended.

    • lastVariableResourceStatementEnd

      private int lastVariableResourceStatementEnd
      Hold the line-number where the last resource variable statement ended.

    • treatTryResourcesAsStatement

      private boolean treatTryResourcesAsStatement
      Enable resources processing.

  • Constructor Details

    • OneStatementPerLineCheck

      public OneStatementPerLineCheck()

  • Method Details

    • setTreatTryResourcesAsStatement

      public void setTreatTryResourcesAsStatement(boolean treatTryResourcesAsStatement)
      Setter to enable resources processing.
      Parameters:
      treatTryResourcesAsStatement - user's value of treatTryResourcesAsStatement.

    • 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:

    • 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:

    • 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:

    • 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

    • 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

    • checkIfSemicolonIsInDifferentLineThanPrevious

      private void checkIfSemicolonIsInDifferentLineThanPrevious(DetailAST ast)
      Checks if given semicolon is in different line than previous.
      Parameters:
      ast - semicolon to check

    • checkLambda

      private void checkLambda(DetailAST ast, DetailAST currentStatement)
      Checks semicolon placement in lambda.
      Parameters:
      ast - semicolon to check
      currentStatement - current statement

    • isResource

      private static boolean isResource(DetailAST ast)
      Checks that given node is a resource.
      Parameters:
      ast - semicolon to check
      Returns:
      true if node is a resource

    • checkResourceVariable

      private void checkResourceVariable(DetailAST currentStatement)
      Checks resource variable.
      Parameters:
      currentStatement - current statement

    • isOnTheSameLine

      private static boolean isOnTheSameLine(DetailAST ast, int lastStatementEnd, int forStatementEnd, int lambdaStatementEnd)
      Checks whether two statements are on the same line.
      Parameters:
      ast - token for the current statement.
      lastStatementEnd - the line-number where the last statement ended.
      forStatementEnd - the line-number where the last 'for-loop' statement ended.
      lambdaStatementEnd - the line-number where the last lambda statement ended.
      Returns:
      true if two statements are on the same line.

    • isMultilineStatement

      private static boolean isMultilineStatement(DetailAST ast)
      Checks whether statement is multiline.
      Parameters:
      ast - token for the current statement.
      Returns:
      true if one statement is distributed over two or more lines.