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

Class UnnecessaryParenthesesCheck

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

Checks if unnecessary parentheses are used in a statement or expression. The check will flag the following with warnings: 

 return (x);          // parens around identifier
 return (x + 1);      // parens around return value
 int x = (y / 2 + 1); // parens around assignment rhs
 for (int i = (0); i < 10; i++) {  // parens around literal
 t -= (z + 1);                     // parens around assignment rhs
 boolean a = (x > 7 && y > 5)      // parens around expression
             || z < 9;
 boolean b = (~a) > -27            // parens around ~a
             && (a-- < 30);        // parens around expression

The check is not "type aware", that is to say, it can't tell if parentheses are unnecessary based on the types in an expression. The check is partially aware about operator precedence but unaware about operator associativity. It won't catch cases such as: 

 int x = (a + b) + c; // 1st Case
 boolean p = true; // 2nd Case
 int q = 4;
 int r = 3;
 if (p == (q <= r)) {}

In the first case, given that a, b, and c are all int variables, the parentheses around a + b are not needed. In the second case, parentheses are required as q, r are of type int and p is of type boolean and removing parentheses will give a compile time error. Even if q and r were boolean still there will be no violation raised as check is not "type aware".

The partial support for operator precedence includes cases of the following type: 

 boolean a = true, b = true;
 boolean c = false, d = false;
 if ((a && b) || c) { // violation, unnecessary paren
 }
 if (a && (b || c)) { // ok
 }
 if ((a == b) && c) { // violation, unnecessary paren
 }
 String e = "e";
 if ((e instanceof String) && a || b) { // violation, unnecessary paren
 }
 int f = 0;
 int g = 0;
 if (!(f >= g) // ok
         && (g > f)) { // violation, unnecessary paren
 }
 if ((++f) > g && a) { // violation, unnecessary paren
 }

To configure the check: 

 <module name="UnnecessaryParentheses"/>

Which results in the following violations: 

 public int square(int a, int b){
   int square = (a * b); // violation
   return (square);      // violation
 }
 int sumOfSquares = 0;
 for(int i=(0); i<10; i++){          // violation
   int x = (i + 1);                  // violation
   sumOfSquares += (square(x * x));  // violation
 }
 double num = (10.0); //violation
 List<String> list = Arrays.asList("a1", "b1", "c1");
 myList.stream()
   .filter((s) -> s.startsWith("c")) // violation
   .forEach(System.out::println);
 int a = 10, b = 12, c = 15;
 boolean x = true, y = false, z= true;
 if ((a >= 0 && b <= 9)            // violation, unnecessary parenthesis
          || (c >= 5 && b <= 5)    // violation, unnecessary parenthesis
          || (c >= 3 && a <= 7)) { // violation, unnecessary parenthesis
     return;
 }
 if ((-a) != -27 // violation, unnecessary parenthesis
          && b > 5) {
     return;
 }
 if (x==(a <= 15)) { // ok
     return;
 }
 if (x==(y == z)) { // ok
     return;
 }

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

  • unnecessary.paren.assign
  • unnecessary.paren.expr
  • unnecessary.paren.ident
  • unnecessary.paren.lambda
  • unnecessary.paren.literal
  • unnecessary.paren.return
  • unnecessary.paren.string
Since:
3.4

  • Field Details

    • MSG_IDENT

      public static final String MSG_IDENT
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • MSG_ASSIGN

      public static final String MSG_ASSIGN
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • MSG_EXPR

      public static final String MSG_EXPR
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • MSG_LITERAL

      public static final String MSG_LITERAL
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • MSG_STRING

      public static final String MSG_STRING
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • MSG_RETURN

      public static final String MSG_RETURN
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • MSG_LAMBDA

      public static final String MSG_LAMBDA
      A key is pointing to the warning message text in "messages.properties" file.
      See Also:

    • NEWLINE

      private static final Pattern NEWLINE
      Compiled pattern used to match newline control characters, for replacement.

    • QUOTE

      private static final String QUOTE
      String used to amend TEXT_BLOCK_CONTENT so that it matches STRING_LITERAL.
      See Also:

    • MAX_QUOTED_LENGTH

      private static final int MAX_QUOTED_LENGTH
      The maximum string length before we chop the string.
      See Also:

    • LITERALS

      private static final int[] LITERALS
      Token types for literals.

    • ASSIGNMENTS

      private static final int[] ASSIGNMENTS
      Token types for assignment operations.

    • CONDITIONALS_AND_RELATIONAL

      private static final int[] CONDITIONALS_AND_RELATIONAL
      Token types for conditional and relational operators.

    • UNARY_AND_POSTFIX

      private static final int[] UNARY_AND_POSTFIX
      Token types for unary and postfix operators.

    • parentToSkip

      private DetailAST parentToSkip
      Used to test if logging a warning in a parent node may be skipped because a warning was already logged on an immediate child node.

    • assignDepth

      private int assignDepth
      Depth of nested assignments. Normally this will be 0 or 1.

  • Constructor Details

    • UnnecessaryParenthesesCheck

      public UnnecessaryParenthesesCheck()

  • 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

    • 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

    • isSurrounded

      private static boolean isSurrounded(DetailAST ast)
      Tests if the given DetailAST is surrounded by parentheses. In short, does ast have a previous sibling whose type is TokenTypes.LPAREN and a next sibling whose type is TokenTypes.RPAREN.
      Parameters:
      ast - the DetailAST to check if it is surrounded by parentheses.
      Returns:
      true if ast is surrounded by parentheses.

    • isExprSurrounded

      private static boolean isExprSurrounded(DetailAST ast)
      Tests if the given expression node is surrounded by parentheses.
      Parameters:
      ast - a DetailAST whose type is TokenTypes.EXPR.
      Returns:
      true if the expression is surrounded by parentheses.

    • checkExpression

      private void checkExpression(DetailAST ast)
      Checks whether an expression is surrounded by parentheses.
      Parameters:
      ast - the DetailAST to check if it is surrounded by parentheses.

    • unnecessaryParenAroundOperators

      private static boolean unnecessaryParenAroundOperators(DetailAST ast)
      Checks if conditional, relational, unary and postfix operators in expressions are surrounded by unnecessary parentheses.
      Parameters:
      ast - the DetailAST to check if it is surrounded by unnecessary parentheses.
      Returns:
      true if the expression is surrounded by unnecessary parentheses.

    • isLambdaSingleParameterSurrounded

      private static boolean isLambdaSingleParameterSurrounded(DetailAST ast)
      Tests if the given lambda node has a single parameter, no defined type, and is surrounded by parentheses.
      Parameters:
      ast - a DetailAST whose type is TokenTypes.LAMBDA.
      Returns:
      true if the lambda has a single parameter, no defined type, and is surrounded by parentheses.

    • chopString

      private static String chopString(String value)
      Returns the specified string chopped to MAX_QUOTED_LENGTH plus an ellipsis (...) if the length of the string exceeds MAX_QUOTED_LENGTH.
      Parameters:
      value - the string to potentially chop.
      Returns:
      the chopped string if string is longer than MAX_QUOTED_LENGTH; otherwise string.