001//////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code for adherence to a set of rules. 003// Copyright (C) 2001-2015 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 antlr.collections.AST; 023 024import com.puppycrawl.tools.checkstyle.api.Check; 025import com.puppycrawl.tools.checkstyle.api.DetailAST; 026import com.puppycrawl.tools.checkstyle.api.TokenTypes; 027 028/** 029 * <p>Checks that string literals are not used with 030 * {@code ==} or {@code !=}. 031 * </p> 032 * <p> 033 * Rationale: Novice Java programmers often use code like 034 * {@code if (x == "something")} when they mean 035 * {@code if ("something".equals(x))}. 036 * </p> 037 * 038 * @author Lars Kühne 039 */ 040public class StringLiteralEqualityCheck extends Check { 041 042 /** 043 * A key is pointing to the warning message text in "messages.properties" 044 * file. 045 */ 046 public static final String MSG_KEY = "string.literal.equality"; 047 048 @Override 049 public int[] getDefaultTokens() { 050 return getAcceptableTokens(); 051 } 052 053 @Override 054 public int[] getAcceptableTokens() { 055 return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL}; 056 } 057 058 @Override 059 public int[] getRequiredTokens() { 060 return getAcceptableTokens(); 061 } 062 063 @Override 064 public void visitToken(DetailAST ast) { 065 // no need to check for nulls here, == and != always have two children 066 final AST firstChild = ast.getFirstChild(); 067 final AST secondChild = firstChild.getNextSibling(); 068 069 if (firstChild.getType() == TokenTypes.STRING_LITERAL 070 || secondChild.getType() == TokenTypes.STRING_LITERAL) { 071 log(ast.getLineNo(), ast.getColumnNo(), 072 MSG_KEY, ast.getText()); 073 } 074 } 075}