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.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 * Make sure that utility classes (classes that contain only static methods)
029 * do not have a public constructor.
030 * <p>
031 * Rationale: Instantiating utility classes does not make sense.
032 * A common mistake is forgetting to hide the default constructor.
033 * </p>
034 *
035 * @author lkuehne
036 */
037@StatelessCheck
038public class HideUtilityClassConstructorCheck extends AbstractCheck {
039
040    /**
041     * A key is pointing to the warning message text in "messages.properties"
042     * file.
043     */
044    public static final String MSG_KEY = "hide.utility.class";
045
046    @Override
047    public int[] getDefaultTokens() {
048        return getRequiredTokens();
049    }
050
051    @Override
052    public int[] getAcceptableTokens() {
053        return getRequiredTokens();
054    }
055
056    @Override
057    public int[] getRequiredTokens() {
058        return new int[] {TokenTypes.CLASS_DEF};
059    }
060
061    @Override
062    public void visitToken(DetailAST ast) {
063        // abstract class could not have private constructor
064        if (!isAbstract(ast)) {
065            final boolean hasStaticModifier = isStatic(ast);
066
067            final Details details = new Details(ast);
068            details.invoke();
069
070            final boolean hasDefaultCtor = details.isHasDefaultCtor();
071            final boolean hasPublicCtor = details.isHasPublicCtor();
072            final boolean hasMethodOrField = details.isHasMethodOrField();
073            final boolean hasNonStaticMethodOrField = details.isHasNonStaticMethodOrField();
074            final boolean hasNonPrivateStaticMethodOrField =
075                    details.isHasNonPrivateStaticMethodOrField();
076
077            final boolean hasAccessibleCtor = hasDefaultCtor || hasPublicCtor;
078
079            // figure out if class extends java.lang.object directly
080            // keep it simple for now and get a 99% solution
081            final boolean extendsJlo =
082                ast.findFirstToken(TokenTypes.EXTENDS_CLAUSE) == null;
083
084            final boolean isUtilClass = extendsJlo && hasMethodOrField
085                && !hasNonStaticMethodOrField && hasNonPrivateStaticMethodOrField;
086
087            if (isUtilClass && hasAccessibleCtor && !hasStaticModifier) {
088                log(ast.getLineNo(), ast.getColumnNo(), MSG_KEY);
089            }
090        }
091    }
092
093    /**
094     * Returns true if given class is abstract or false.
095     * @param ast class definition for check.
096     * @return true if a given class declared as abstract.
097     */
098    private static boolean isAbstract(DetailAST ast) {
099        return ast.findFirstToken(TokenTypes.MODIFIERS)
100            .findFirstToken(TokenTypes.ABSTRACT) != null;
101    }
102
103    /**
104     * Returns true if given class is static or false.
105     * @param ast class definition for check.
106     * @return true if a given class declared as static.
107     */
108    private static boolean isStatic(DetailAST ast) {
109        return ast.findFirstToken(TokenTypes.MODIFIERS)
110            .findFirstToken(TokenTypes.LITERAL_STATIC) != null;
111    }
112
113    /**
114     * Details of class that are required for validation.
115     */
116    private static class Details {
117        /** Class ast. */
118        private final DetailAST ast;
119        /** Result of details gathering. */
120        private boolean hasMethodOrField;
121        /** Result of details gathering. */
122        private boolean hasNonStaticMethodOrField;
123        /** Result of details gathering. */
124        private boolean hasNonPrivateStaticMethodOrField;
125        /** Result of details gathering. */
126        private boolean hasDefaultCtor;
127        /** Result of details gathering. */
128        private boolean hasPublicCtor;
129
130        /**
131         * C-tor.
132         * @param ast class ast
133         * */
134        Details(DetailAST ast) {
135            this.ast = ast;
136        }
137
138        /**
139         * Getter.
140         * @return boolean
141         */
142        public boolean isHasMethodOrField() {
143            return hasMethodOrField;
144        }
145
146        /**
147         * Getter.
148         * @return boolean
149         */
150        public boolean isHasNonStaticMethodOrField() {
151            return hasNonStaticMethodOrField;
152        }
153
154        /**
155         * Getter.
156         * @return boolean
157         */
158        public boolean isHasNonPrivateStaticMethodOrField() {
159            return hasNonPrivateStaticMethodOrField;
160        }
161
162        /**
163         * Getter.
164         * @return boolean
165         */
166        public boolean isHasDefaultCtor() {
167            return hasDefaultCtor;
168        }
169
170        /**
171         * Getter.
172         * @return boolean
173         */
174        public boolean isHasPublicCtor() {
175            return hasPublicCtor;
176        }
177
178        /**
179         * Main method to gather statistics.
180         */
181        public void invoke() {
182            final DetailAST objBlock = ast.findFirstToken(TokenTypes.OBJBLOCK);
183            hasMethodOrField = false;
184            hasNonStaticMethodOrField = false;
185            hasNonPrivateStaticMethodOrField = false;
186            hasDefaultCtor = true;
187            hasPublicCtor = false;
188            DetailAST child = objBlock.getFirstChild();
189
190            while (child != null) {
191                final int type = child.getType();
192                if (type == TokenTypes.METHOD_DEF
193                        || type == TokenTypes.VARIABLE_DEF) {
194                    hasMethodOrField = true;
195                    final DetailAST modifiers =
196                        child.findFirstToken(TokenTypes.MODIFIERS);
197                    final boolean isStatic =
198                        modifiers.findFirstToken(TokenTypes.LITERAL_STATIC) != null;
199                    final boolean isPrivate =
200                        modifiers.findFirstToken(TokenTypes.LITERAL_PRIVATE) != null;
201
202                    if (!isStatic) {
203                        hasNonStaticMethodOrField = true;
204                    }
205                    if (isStatic && !isPrivate) {
206                        hasNonPrivateStaticMethodOrField = true;
207                    }
208                }
209                if (type == TokenTypes.CTOR_DEF) {
210                    hasDefaultCtor = false;
211                    final DetailAST modifiers =
212                        child.findFirstToken(TokenTypes.MODIFIERS);
213                    if (modifiers.findFirstToken(TokenTypes.LITERAL_PRIVATE) == null
214                        && modifiers.findFirstToken(TokenTypes.LITERAL_PROTECTED) == null) {
215                        // treat package visible as public
216                        // for the purpose of this Check
217                        hasPublicCtor = true;
218                    }
219
220                }
221                child = child.getNextSibling();
222            }
223        }
224    }
225}