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Checkstyle is a development tool to help programmers write Java code
that adheres to a coding standard
////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2019 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
////////////////////////////////////////////////////////////////////////////////
package com.puppycrawl.tools.checkstyle.checks.coding;
import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
/**
*
* 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
*
* 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. It also doesn't know
* about operator precedence and associativity; therefore it won't catch
* something like
*
*
* int x = (a + b) + c;
*
* In the above case, given that a, b, and c are
* all {@code int} variables, the parentheses around {@code a + b}
* are not needed.
*
*
* -
* Property {@code tokens} - tokens to check
* 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.
*
*
*
* 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);
*
*
* @since 3.4
*/
@FileStatefulCheck
public class UnnecessaryParenthesesCheck extends AbstractCheck {
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_IDENT = "unnecessary.paren.ident";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_ASSIGN = "unnecessary.paren.assign";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_EXPR = "unnecessary.paren.expr";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_LITERAL = "unnecessary.paren.literal";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_STRING = "unnecessary.paren.string";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_RETURN = "unnecessary.paren.return";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_LAMBDA = "unnecessary.paren.lambda";
/** The maximum string length before we chop the string. */
private static final int MAX_QUOTED_LENGTH = 25;
/** Token types for literals. */
private static final int[] LITERALS = {
TokenTypes.NUM_DOUBLE,
TokenTypes.NUM_FLOAT,
TokenTypes.NUM_INT,
TokenTypes.NUM_LONG,
TokenTypes.STRING_LITERAL,
TokenTypes.LITERAL_NULL,
TokenTypes.LITERAL_FALSE,
TokenTypes.LITERAL_TRUE,
};
/** Token types for assignment operations. */
private static final int[] ASSIGNMENTS = {
TokenTypes.ASSIGN,
TokenTypes.BAND_ASSIGN,
TokenTypes.BOR_ASSIGN,
TokenTypes.BSR_ASSIGN,
TokenTypes.BXOR_ASSIGN,
TokenTypes.DIV_ASSIGN,
TokenTypes.MINUS_ASSIGN,
TokenTypes.MOD_ASSIGN,
TokenTypes.PLUS_ASSIGN,
TokenTypes.SL_ASSIGN,
TokenTypes.SR_ASSIGN,
TokenTypes.STAR_ASSIGN,
};
/**
* 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 DetailAST parentToSkip;
/** Depth of nested assignments. Normally this will be 0 or 1. */
private int assignDepth;
@Override
public int[] getDefaultTokens() {
return new int[] {
TokenTypes.EXPR,
TokenTypes.IDENT,
TokenTypes.NUM_DOUBLE,
TokenTypes.NUM_FLOAT,
TokenTypes.NUM_INT,
TokenTypes.NUM_LONG,
TokenTypes.STRING_LITERAL,
TokenTypes.LITERAL_NULL,
TokenTypes.LITERAL_FALSE,
TokenTypes.LITERAL_TRUE,
TokenTypes.ASSIGN,
TokenTypes.BAND_ASSIGN,
TokenTypes.BOR_ASSIGN,
TokenTypes.BSR_ASSIGN,
TokenTypes.BXOR_ASSIGN,
TokenTypes.DIV_ASSIGN,
TokenTypes.MINUS_ASSIGN,
TokenTypes.MOD_ASSIGN,
TokenTypes.PLUS_ASSIGN,
TokenTypes.SL_ASSIGN,
TokenTypes.SR_ASSIGN,
TokenTypes.STAR_ASSIGN,
TokenTypes.LAMBDA,
};
}
@Override
public int[] getAcceptableTokens() {
return new int[] {
TokenTypes.EXPR,
TokenTypes.IDENT,
TokenTypes.NUM_DOUBLE,
TokenTypes.NUM_FLOAT,
TokenTypes.NUM_INT,
TokenTypes.NUM_LONG,
TokenTypes.STRING_LITERAL,
TokenTypes.LITERAL_NULL,
TokenTypes.LITERAL_FALSE,
TokenTypes.LITERAL_TRUE,
TokenTypes.ASSIGN,
TokenTypes.BAND_ASSIGN,
TokenTypes.BOR_ASSIGN,
TokenTypes.BSR_ASSIGN,
TokenTypes.BXOR_ASSIGN,
TokenTypes.DIV_ASSIGN,
TokenTypes.MINUS_ASSIGN,
TokenTypes.MOD_ASSIGN,
TokenTypes.PLUS_ASSIGN,
TokenTypes.SL_ASSIGN,
TokenTypes.SR_ASSIGN,
TokenTypes.STAR_ASSIGN,
TokenTypes.LAMBDA,
};
}
@Override
public int[] getRequiredTokens() {
// Check can work with any of acceptable tokens
return CommonUtil.EMPTY_INT_ARRAY;
}
// -@cs[CyclomaticComplexity] All logs should be in visit token.
@Override
public void visitToken(DetailAST ast) {
final int type = ast.getType();
final DetailAST parent = ast.getParent();
if (type == TokenTypes.LAMBDA && isLambdaSingleParameterSurrounded(ast)) {
log(ast, MSG_LAMBDA, ast.getText());
}
else if (type != TokenTypes.ASSIGN
|| parent.getType() != TokenTypes.ANNOTATION_MEMBER_VALUE_PAIR) {
final boolean surrounded = isSurrounded(ast);
// An identifier surrounded by parentheses.
if (surrounded && type == TokenTypes.IDENT) {
parentToSkip = ast.getParent();
log(ast, MSG_IDENT, ast.getText());
}
// A literal (numeric or string) surrounded by parentheses.
else if (surrounded && isInTokenList(type, LITERALS)) {
parentToSkip = ast.getParent();
if (type == TokenTypes.STRING_LITERAL) {
log(ast, MSG_STRING,
chopString(ast.getText()));
}
else {
log(ast, MSG_LITERAL, ast.getText());
}
}
// The rhs of an assignment surrounded by parentheses.
else if (isInTokenList(type, ASSIGNMENTS)) {
assignDepth++;
final DetailAST last = ast.getLastChild();
if (last.getType() == TokenTypes.RPAREN) {
log(ast, MSG_ASSIGN);
}
}
}
}
@Override
public void leaveToken(DetailAST ast) {
final int type = ast.getType();
final DetailAST parent = ast.getParent();
// shouldn't process assign in annotation pairs
if (type != TokenTypes.ASSIGN
|| parent.getType() != TokenTypes.ANNOTATION_MEMBER_VALUE_PAIR) {
// An expression is surrounded by parentheses.
if (type == TokenTypes.EXPR) {
// If 'parentToSkip' == 'ast', then we've already logged a
// warning about an immediate child node in visitToken, so we don't
// need to log another one here.
if (parentToSkip != ast && isExprSurrounded(ast)) {
if (assignDepth >= 1) {
log(ast, MSG_ASSIGN);
}
else if (ast.getParent().getType() == TokenTypes.LITERAL_RETURN) {
log(ast, MSG_RETURN);
}
else {
log(ast, MSG_EXPR);
}
}
parentToSkip = null;
}
else if (isInTokenList(type, ASSIGNMENTS)) {
assignDepth--;
}
}
}
/**
* Tests if the given {@code DetailAST} is surrounded by parentheses.
* In short, does {@code ast} have a previous sibling whose type is
* {@code TokenTypes.LPAREN} and a next sibling whose type is {@code
* TokenTypes.RPAREN}.
* @param ast the {@code DetailAST} to check if it is surrounded by
* parentheses.
* @return {@code true} if {@code ast} is surrounded by
* parentheses.
*/
private static boolean isSurrounded(DetailAST ast) {
// if previous sibling is left parenthesis,
// next sibling can't be other than right parenthesis
final DetailAST prev = ast.getPreviousSibling();
return prev != null && prev.getType() == TokenTypes.LPAREN;
}
/**
* Tests if the given expression node is surrounded by parentheses.
* @param ast a {@code DetailAST} whose type is
* {@code TokenTypes.EXPR}.
* @return {@code true} if the expression is surrounded by
* parentheses.
*/
private static boolean isExprSurrounded(DetailAST ast) {
return ast.getFirstChild().getType() == TokenTypes.LPAREN;
}
/**
* Tests if the given lambda node has a single parameter, no defined type, and is surrounded
* by parentheses.
* @param ast a {@code DetailAST} whose type is
* {@code TokenTypes.LAMBDA}.
* @return {@code true} if the lambda has a single parameter, no defined type, and is
* surrounded by parentheses.
*/
private static boolean isLambdaSingleParameterSurrounded(DetailAST ast) {
final DetailAST firstChild = ast.getFirstChild();
return firstChild.getType() == TokenTypes.LPAREN
&& firstChild.getNextSibling().getChildCount(TokenTypes.PARAMETER_DEF) == 1
&& firstChild.getNextSibling().getFirstChild().findFirstToken(TokenTypes.TYPE)
.getChildCount() == 0;
}
/**
* Check if the given token type can be found in an array of token types.
* @param type the token type.
* @param tokens an array of token types to search.
* @return {@code true} if {@code type} was found in {@code
* tokens}.
*/
private static boolean isInTokenList(int type, int... tokens) {
// NOTE: Given the small size of the two arrays searched, I'm not sure
// it's worth bothering with doing a binary search or using a
// HashMap to do the searches.
boolean found = false;
for (int i = 0; i < tokens.length && !found; i++) {
found = tokens[i] == type;
}
return found;
}
/**
* Returns the specified string chopped to {@code MAX_QUOTED_LENGTH}
* plus an ellipsis (...) if the length of the string exceeds {@code
* MAX_QUOTED_LENGTH}.
* @param value the string to potentially chop.
* @return the chopped string if {@code string} is longer than
* {@code MAX_QUOTED_LENGTH}; otherwise {@code string}.
*/
private static String chopString(String value) {
String result = value;
if (value.length() > MAX_QUOTED_LENGTH) {
result = value.substring(0, MAX_QUOTED_LENGTH) + "...\"";
}
return result;
}
}