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

Class 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 Detail

      • MSG_IDENT

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

      • MSG_ASSIGN

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

      • MSG_EXPR

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

      • MSG_LITERAL

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

      • MSG_STRING

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

      • MSG_RETURN

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

      • MSG_LAMBDA

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

      • NEWLINE

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

      • QUOTE

        private static final java.lang.String QUOTE
        String used to amend TEXT_BLOCK_CONTENT so that it matches STRING_LITERAL.
        See Also:
        Constant Field Values

      • 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.

    • Method Detail

      • 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

      • 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 java.lang.String chopString​(java.lang.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.