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}