001//////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code for adherence to a set of rules. 003// Copyright (C) 2001-2017 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.api.AbstractCheck; 023import com.puppycrawl.tools.checkstyle.api.DetailAST; 024import com.puppycrawl.tools.checkstyle.api.TokenTypes; 025 026/** 027 * Implements Bloch, Effective Java, Item 17 - 028 * Use Interfaces only to define types. 029 * 030 * <p> 031 * An interface should describe a <em>type</em>, it is therefore 032 * inappropriate to define an interface that does not contain any methods 033 * but only constants. 034 * </p> 035 * 036 * <p> 037 * The check can be configured to also disallow marker interfaces like 038 * {@code java.io.Serializable}, that do not contain methods or 039 * constants at all. 040 * </p> 041 * 042 * @author lkuehne 043 */ 044public final class InterfaceIsTypeCheck 045 extends AbstractCheck { 046 047 /** 048 * A key is pointing to the warning message text in "messages.properties" 049 * file. 050 */ 051 public static final String MSG_KEY = "interface.type"; 052 053 /** Flag to control whether marker interfaces are allowed. */ 054 private boolean allowMarkerInterfaces = true; 055 056 @Override 057 public int[] getDefaultTokens() { 058 return new int[] {TokenTypes.INTERFACE_DEF}; 059 } 060 061 @Override 062 public int[] getRequiredTokens() { 063 return getDefaultTokens(); 064 } 065 066 @Override 067 public int[] getAcceptableTokens() { 068 return new int[] {TokenTypes.INTERFACE_DEF}; 069 } 070 071 @Override 072 public void visitToken(DetailAST ast) { 073 final DetailAST objBlock = 074 ast.findFirstToken(TokenTypes.OBJBLOCK); 075 final DetailAST methodDef = 076 objBlock.findFirstToken(TokenTypes.METHOD_DEF); 077 final DetailAST variableDef = 078 objBlock.findFirstToken(TokenTypes.VARIABLE_DEF); 079 final boolean methodRequired = 080 !allowMarkerInterfaces || variableDef != null; 081 082 if (methodDef == null && methodRequired) { 083 log(ast.getLineNo(), MSG_KEY); 084 } 085 086 } 087 088 /** 089 * Controls whether marker interfaces like Serializable are allowed. 090 * @param flag whether to allow marker interfaces or not 091 */ 092 public void setAllowMarkerInterfaces(boolean flag) { 093 allowMarkerInterfaces = flag; 094 } 095}