001//////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code for adherence to a set of rules. 003// Copyright (C) 2001-2018 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.design; 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 * Implements Bloch, Effective Java, Item 17 - 029 * Use Interfaces only to define types. 030 * 031 * <p> 032 * An interface should describe a <em>type</em>, it is therefore 033 * inappropriate to define an interface that does not contain any methods 034 * but only constants. 035 * </p> 036 * 037 * <p> 038 * The check can be configured to also disallow marker interfaces like 039 * {@code java.io.Serializable}, that do not contain methods or 040 * constants at all. 041 * </p> 042 * 043 * @author lkuehne 044 */ 045@StatelessCheck 046public final class InterfaceIsTypeCheck 047 extends AbstractCheck { 048 049 /** 050 * A key is pointing to the warning message text in "messages.properties" 051 * file. 052 */ 053 public static final String MSG_KEY = "interface.type"; 054 055 /** Flag to control whether marker interfaces are allowed. */ 056 private boolean allowMarkerInterfaces = true; 057 058 @Override 059 public int[] getDefaultTokens() { 060 return getRequiredTokens(); 061 } 062 063 @Override 064 public int[] getRequiredTokens() { 065 return new int[] {TokenTypes.INTERFACE_DEF}; 066 } 067 068 @Override 069 public int[] getAcceptableTokens() { 070 return getRequiredTokens(); 071 } 072 073 @Override 074 public void visitToken(DetailAST ast) { 075 final DetailAST objBlock = 076 ast.findFirstToken(TokenTypes.OBJBLOCK); 077 final DetailAST methodDef = 078 objBlock.findFirstToken(TokenTypes.METHOD_DEF); 079 final DetailAST variableDef = 080 objBlock.findFirstToken(TokenTypes.VARIABLE_DEF); 081 final boolean methodRequired = 082 !allowMarkerInterfaces || variableDef != null; 083 084 if (methodDef == null && methodRequired) { 085 log(ast.getLineNo(), MSG_KEY); 086 } 087 } 088 089 /** 090 * Controls whether marker interfaces like Serializable are allowed. 091 * @param flag whether to allow marker interfaces or not 092 */ 093 public void setAllowMarkerInterfaces(boolean flag) { 094 allowMarkerInterfaces = flag; 095 } 096 097}