001/////////////////////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code and other text files for adherence to a set of rules. 003// Copyright (C) 2001-2025 the original author or authors. 004// 005// This library is free software; you can redistribute it and/or 006// modify it under the terms of the GNU Lesser General Public 007// License as published by the Free Software Foundation; either 008// version 2.1 of the License, or (at your option) any later version. 009// 010// This library is distributed in the hope that it will be useful, 011// but WITHOUT ANY WARRANTY; without even the implied warranty of 012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 013// Lesser General Public License for more details. 014// 015// You should have received a copy of the GNU Lesser General Public 016// License along with this library; if not, write to the Free Software 017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 018/////////////////////////////////////////////////////////////////////////////////////////////// 019 020package com.puppycrawl.tools.checkstyle.checks.coding; 021 022import com.puppycrawl.tools.checkstyle.StatelessCheck; 023import com.puppycrawl.tools.checkstyle.api.AbstractCheck; 024import com.puppycrawl.tools.checkstyle.api.DetailAST; 025import com.puppycrawl.tools.checkstyle.api.TokenTypes; 026import com.puppycrawl.tools.checkstyle.utils.TokenUtil; 027 028/** 029 * <div> 030 * Checks for over-complicated boolean return or yield statements. 031 * For example the following code 032 * </div> 033 * <div class="wrapper"><pre class="prettyprint"><code class="language-java"> 034 * if (valid()) 035 * return false; 036 * else 037 * return true; 038 * </code></pre></div> 039 * 040 * <p> 041 * could be written as 042 * </p> 043 * <div class="wrapper"><pre class="prettyprint"><code class="language-java"> 044 * return !valid(); 045 * </code></pre></div> 046 * 047 * <p> 048 * The idea for this Check has been shamelessly stolen from the equivalent 049 * <a href="https://pmd.github.io/pmd/pmd_rules_java_design.html#simplifybooleanreturns"> 050 * PMD</a> rule. 051 * </p> 052 * 053 * @since 3.0 054 */ 055@StatelessCheck 056public class SimplifyBooleanReturnCheck 057 extends AbstractCheck { 058 059 /** 060 * A key is pointing to the warning message text in "messages.properties" 061 * file. 062 */ 063 public static final String MSG_KEY = "simplify.boolReturn"; 064 065 @Override 066 public int[] getAcceptableTokens() { 067 return getRequiredTokens(); 068 } 069 070 @Override 071 public int[] getDefaultTokens() { 072 return getRequiredTokens(); 073 } 074 075 @Override 076 public int[] getRequiredTokens() { 077 return new int[] {TokenTypes.LITERAL_IF}; 078 } 079 080 @Override 081 public void visitToken(DetailAST ast) { 082 // LITERAL_IF has the following four or five children: 083 // '(' 084 // condition 085 // ')' 086 // thenStatement 087 // [ LITERAL_ELSE (with the elseStatement as a child) ] 088 089 // don't bother if this is not if then else 090 final DetailAST elseLiteral = 091 ast.findFirstToken(TokenTypes.LITERAL_ELSE); 092 if (elseLiteral != null) { 093 final DetailAST elseStatement = elseLiteral.getFirstChild(); 094 095 // skip '(' and ')' 096 final DetailAST condition = ast.getFirstChild().getNextSibling(); 097 final DetailAST thenStatement = condition.getNextSibling().getNextSibling(); 098 099 if (canReturnOrYieldOnlyBooleanLiteral(thenStatement) 100 && canReturnOrYieldOnlyBooleanLiteral(elseStatement)) { 101 log(ast, MSG_KEY); 102 } 103 } 104 } 105 106 /** 107 * Returns if an AST is a return or a yield statement with a boolean literal 108 * or a compound statement that contains only such a return or a yield statement. 109 * 110 * <p>Returns {@code true} iff ast represents 111 * <pre> 112 * return/yield true/false; 113 * </pre> 114 * or 115 * <pre> 116 * { 117 * return/yield true/false; 118 * } 119 * </pre> 120 * 121 * @param ast the syntax tree to check 122 * @return if ast is a return or a yield statement with a boolean literal. 123 */ 124 private static boolean canReturnOrYieldOnlyBooleanLiteral(DetailAST ast) { 125 boolean result = true; 126 if (!isBooleanLiteralReturnOrYieldStatement(ast)) { 127 final DetailAST firstStatement = ast.getFirstChild(); 128 result = isBooleanLiteralReturnOrYieldStatement(firstStatement); 129 } 130 return result; 131 } 132 133 /** 134 * Returns if an AST is a return or a yield statement with a boolean literal. 135 * 136 * <p>Returns {@code true} iff ast represents 137 * <pre> 138 * return/yield true/false; 139 * </pre> 140 * 141 * @param ast the syntax tree to check 142 * @return if ast is a return or a yield statement with a boolean literal. 143 */ 144 private static boolean isBooleanLiteralReturnOrYieldStatement(DetailAST ast) { 145 boolean booleanReturnStatement = false; 146 147 if (ast != null && (ast.getType() == TokenTypes.LITERAL_RETURN 148 || ast.getType() == TokenTypes.LITERAL_YIELD)) { 149 final DetailAST expr = ast.getFirstChild(); 150 151 if (expr.getType() != TokenTypes.SEMI) { 152 final DetailAST value = expr.getFirstChild(); 153 booleanReturnStatement = TokenUtil.isBooleanLiteralType(value.getType()); 154 } 155 } 156 return booleanReturnStatement; 157 } 158}