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 java.util.BitSet; 023import java.util.function.Predicate; 024 025import com.puppycrawl.tools.checkstyle.StatelessCheck; 026import com.puppycrawl.tools.checkstyle.api.AbstractCheck; 027import com.puppycrawl.tools.checkstyle.api.DetailAST; 028import com.puppycrawl.tools.checkstyle.api.TokenTypes; 029import com.puppycrawl.tools.checkstyle.utils.TokenUtil; 030 031/** 032 * <div> 033 * Detects double brace initialization. 034 * </div> 035 * 036 * <p> 037 * Rationale: Double brace initialization (set of 038 * <a href="https://docs.oracle.com/javase/specs/jls/se12/html/jls-8.html#jls-8.6"> 039 * Instance Initializers</a> in class body) may look cool, but it is considered as anti-pattern 040 * and should be avoided. 041 * This is also can lead to a hard-to-detect memory leak, if the anonymous class instance is 042 * returned outside and other object(s) hold reference to it. 043 * Created anonymous class is not static, it holds an implicit reference to the outer class 044 * instance. 045 * See this 046 * <a href="https://blog.jooq.org/dont-be-clever-the-double-curly-braces-anti-pattern/"> 047 * blog post</a> and 048 * <a href="https://www.baeldung.com/java-double-brace-initialization"> 049 * article</a> for more details. 050 * Check ignores any comments and semicolons in class body. 051 * </p> 052 * 053 * <p> 054 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker} 055 * </p> 056 * 057 * <p> 058 * Violation Message Keys: 059 * </p> 060 * <ul> 061 * <li> 062 * {@code avoid.double.brace.init} 063 * </li> 064 * </ul> 065 * 066 * @since 8.30 067 */ 068@StatelessCheck 069public class AvoidDoubleBraceInitializationCheck extends AbstractCheck { 070 071 /** 072 * A key is pointing to the warning message text in "messages.properties" 073 * file. 074 */ 075 public static final String MSG_KEY = "avoid.double.brace.init"; 076 077 /** 078 * Set of token types that are used in {@link #HAS_MEMBERS} predicate. 079 */ 080 private static final BitSet IGNORED_TYPES = TokenUtil.asBitSet( 081 TokenTypes.INSTANCE_INIT, 082 TokenTypes.SEMI, 083 TokenTypes.LCURLY, 084 TokenTypes.RCURLY 085 ); 086 087 /** 088 * Predicate for tokens that is used in {@link #hasOnlyInitialization(DetailAST)}. 089 */ 090 private static final Predicate<DetailAST> HAS_MEMBERS = 091 token -> !IGNORED_TYPES.get(token.getType()); 092 093 @Override 094 public int[] getDefaultTokens() { 095 return getRequiredTokens(); 096 } 097 098 @Override 099 public int[] getAcceptableTokens() { 100 return getRequiredTokens(); 101 } 102 103 @Override 104 public int[] getRequiredTokens() { 105 return new int[] {TokenTypes.OBJBLOCK}; 106 } 107 108 @Override 109 public void visitToken(DetailAST ast) { 110 if (ast.getParent().getType() == TokenTypes.LITERAL_NEW 111 && hasOnlyInitialization(ast)) { 112 log(ast, MSG_KEY); 113 } 114 } 115 116 /** 117 * Checks that block has at least one instance init block and no other class members. 118 * 119 * @param objBlock token to check 120 * @return true if there is least one instance init block and no other class members, 121 * false otherwise 122 */ 123 private static boolean hasOnlyInitialization(DetailAST objBlock) { 124 final boolean hasInitBlock = objBlock.findFirstToken(TokenTypes.INSTANCE_INIT) != null; 125 return hasInitBlock 126 && TokenUtil.findFirstTokenByPredicate(objBlock, HAS_MEMBERS).isEmpty(); 127 } 128}