Class 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 Detail

      • 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.
    • Method Detail

      • setTreatTryResourcesAsStatement

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