UnnecessaryParenthesesCheck (checkstyle 9.3 API)

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
 }

Property tokens - tokens to check Type is java.lang.String[]. Validation type is tokenSet. Default value is: EXPR, IDENT, NUM_DOUBLE, NUM_FLOAT, NUM_INT, NUM_LONG, STRING_LITERAL, LITERAL_NULL, LITERAL_FALSE, LITERAL_TRUE, ASSIGN, BAND_ASSIGN, BOR_ASSIGN, BSR_ASSIGN, BXOR_ASSIGN, DIV_ASSIGN, MINUS_ASSIGN, MOD_ASSIGN, PLUS_ASSIGN, SL_ASSIGN, SR_ASSIGN, STAR_ASSIGN, LAMBDA, TEXT_BLOCK_LITERAL_BEGIN, LAND, LOR, LITERAL_INSTANCEOF, GT, LT, GE, LE, EQUAL, NOT_EQUAL, UNARY_MINUS, UNARY_PLUS, INC, DEC, LNOT, BNOT, POST_INC, POST_DEC.

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

Nested Class Summary
- Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean
  AutomaticBean.OutputStreamOptions

Field Summary

Fields
Modifier and Type	Field and Description
`private int`	`assignDepth` Depth of nested assignments.
`private static int[]`	`ASSIGNMENTS` Token types for assignment operations.
`private static int[]`	`CONDITIONALS_AND_RELATIONAL` Token types for conditional and relational operators.
`private static int[]`	`LITERALS` Token types for literals.
`private static int`	`MAX_QUOTED_LENGTH` The maximum string length before we chop the string.
`static java.lang.String`	`MSG_ASSIGN` A key is pointing to the warning message text in "messages.properties" file.
`static java.lang.String`	`MSG_EXPR` A key is pointing to the warning message text in "messages.properties" file.
`static java.lang.String`	`MSG_IDENT` A key is pointing to the warning message text in "messages.properties" file.
`static java.lang.String`	`MSG_LAMBDA` A key is pointing to the warning message text in "messages.properties" file.
`static java.lang.String`	`MSG_LITERAL` A key is pointing to the warning message text in "messages.properties" file.
`static java.lang.String`	`MSG_RETURN` A key is pointing to the warning message text in "messages.properties" file.
`static java.lang.String`	`MSG_STRING` A key is pointing to the warning message text in "messages.properties" file.
`private static java.util.regex.Pattern`	`NEWLINE` Compiled pattern used to match newline control characters, for replacement.
`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.
`private static java.lang.String`	`QUOTE` String used to amend TEXT_BLOCK_CONTENT so that it matches STRING_LITERAL.
`private static int[]`	`UNARY_AND_POSTFIX` Token types for unary and postfix operators.

Constructor Summary

Constructors
Constructor and Description

UnnecessaryParenthesesCheck()

Constructors
Constructor and Description
`UnnecessaryParenthesesCheck()`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`private void`	`checkExpression(DetailAST ast)` Checks whether an expression is surrounded by parentheses.
`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`.
`int[]`	`getAcceptableTokens()` The configurable token set.
`int[]`	`getDefaultTokens()` Returns the default token a check is interested in.
`int[]`	`getRequiredTokens()` The tokens that this check must be registered for.
`private static boolean`	`isExprSurrounded(DetailAST ast)` Tests if the given expression node is surrounded by parentheses.
`private static boolean`	`isLambdaSingleParameterSurrounded(DetailAST ast)` Tests if the given lambda node has a single parameter, no defined type, and is surrounded by parentheses.
`private static boolean`	`isSurrounded(DetailAST ast)` Tests if the given `DetailAST` is surrounded by parentheses.
`void`	`leaveToken(DetailAST ast)` Called after all the child nodes have been process.
`private static boolean`	`unnecessaryParenAroundOperators(DetailAST ast)` Checks if conditional, relational, unary and postfix operators in expressions are surrounded by unnecessary parentheses.
`void`	`visitToken(DetailAST ast)` Called to process a token.

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck
beginTree, clearViolations, destroy, finishTree, getFileContents, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, init, isCommentNodesRequired, log, log, log, setFileContents, setTabWidth, setTokens

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
finishLocalSetup, getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, setId, setSeverity

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean
configure, contextualize, getConfiguration, setupChild

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 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
  - MAX_QUOTED_LENGTH
```
private static final int MAX_QUOTED_LENGTH
```
    The maximum string length before we chop the string.
    
    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.
- Constructor Detail
  - UnnecessaryParenthesesCheck
```
public UnnecessaryParenthesesCheck()
```
- Method Detail
  - 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:
    
    TokenTypes
  - 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
  - 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:
    
    TokenTypes
  - 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 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.

Class UnnecessaryParenthesesCheck

Nested Class Summary

Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

Field Summary

Constructor Summary

Method Summary

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

Methods inherited from class java.lang.Object

Field Detail

MSG_IDENT

MSG_ASSIGN

MSG_EXPR

MSG_LITERAL

MSG_STRING

MSG_RETURN

MSG_LAMBDA

NEWLINE

QUOTE

MAX_QUOTED_LENGTH

LITERALS

ASSIGNMENTS

CONDITIONALS_AND_RELATIONAL

UNARY_AND_POSTFIX

parentToSkip

assignDepth

Constructor Detail

UnnecessaryParenthesesCheck

Method Detail

getDefaultTokens

getAcceptableTokens

getRequiredTokens

visitToken

leaveToken

isSurrounded

isExprSurrounded

checkExpression

unnecessaryParenAroundOperators

isLambdaSingleParameterSurrounded

chopString