001/////////////////////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code and other text files for adherence to a set of rules. 003// Copyright (C) 2001-2024 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; 026 027/** 028 * <p> 029 * Checks that string literals are not used with <code>==</code> or <code>!=</code>. 030 * Since <code>==</code> will compare the object references, not the actual value of the strings, 031 * <code>String.equals()</code> should be used. 032 * More information can be found 033 * <a href="https://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java/"> 034 * in this article</a>. 035 * </p> 036 * <p> 037 * Rationale: Novice Java programmers often use code like: 038 * </p> 039 * <pre> 040 * if (x == "something") 041 * </pre> 042 * <p> 043 * when they mean 044 * </p> 045 * <pre> 046 * if ("something".equals(x)) 047 * </pre> 048 * <p> 049 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker} 050 * </p> 051 * <p> 052 * Violation Message Keys: 053 * </p> 054 * <ul> 055 * <li> 056 * {@code string.literal.equality} 057 * </li> 058 * </ul> 059 * 060 * @since 3.2 061 * @noinspection HtmlTagCanBeJavadocTag 062 * @noinspectionreason HtmlTagCanBeJavadocTag - encoded symbols were not decoded 063 * when replaced with Javadoc tag 064 */ 065@StatelessCheck 066public class StringLiteralEqualityCheck extends AbstractCheck { 067 068 /** 069 * A key is pointing to the warning message text in "messages.properties" 070 * file. 071 */ 072 public static final String MSG_KEY = "string.literal.equality"; 073 074 @Override 075 public int[] getDefaultTokens() { 076 return getRequiredTokens(); 077 } 078 079 @Override 080 public int[] getAcceptableTokens() { 081 return getRequiredTokens(); 082 } 083 084 @Override 085 public int[] getRequiredTokens() { 086 return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL}; 087 } 088 089 @Override 090 public void visitToken(DetailAST ast) { 091 final boolean hasStringLiteralChild = hasStringLiteralChild(ast); 092 093 if (hasStringLiteralChild) { 094 log(ast, MSG_KEY, ast.getText()); 095 } 096 } 097 098 /** 099 * Checks whether string literal or text block literals are concatenated. 100 * 101 * @param ast ast 102 * @return {@code true} if string literal or text block literals are concatenated 103 */ 104 private static boolean hasStringLiteralChild(DetailAST ast) { 105 DetailAST currentAst = ast; 106 boolean result = false; 107 while (currentAst != null) { 108 if (currentAst.findFirstToken(TokenTypes.STRING_LITERAL) == null 109 && currentAst.findFirstToken(TokenTypes.TEXT_BLOCK_LITERAL_BEGIN) == null) { 110 currentAst = currentAst.findFirstToken(TokenTypes.PLUS); 111 } 112 else { 113 result = true; 114 break; 115 } 116 } 117 return result; 118 } 119 120}