Class StringLiteralEqualityCheck

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

Checks that string literals are not used with == or !=. Since == will compare the object references, not the actual value of the strings, String.equals() should be used. More information can be found in this article.

Rationale: Novice Java programmers often use code like: 

if (x == "something")

when they mean 

if ("something".equals(x))

To configure the check: 

<module name="StringLiteralEquality"/>

Examples of violations: 

String status = "pending";

if (status == "done") {} // violation

while (status != "done") {} // violation

boolean flag = (status == "done"); // violation

boolean flag = (status.equals("done")); // OK

String name = "X";

if (name == getName()) {}
// OK, limitation that check cannot tell runtime type returned from method call

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • string.literal.equality
Since:
3.2

  • 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:

  • Constructor Details

    • StringLiteralEqualityCheck

      public StringLiteralEqualityCheck()

  • Method Details

    • 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:

    • 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

    • areStringsConcatenated

      private static boolean areStringsConcatenated(DetailAST ast)
      Checks whether string literal or text block literals are concatenated.
      Parameters:
      ast - ast
      Returns:
      true if string literal or text block literals are concatenated