001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2015 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.Check;
023import com.puppycrawl.tools.checkstyle.api.DetailAST;
024import com.puppycrawl.tools.checkstyle.api.TokenTypes;
025
026/**
027 * Make sure that utility classes (classes that contain only static methods)
028 * do not have a public constructor.
029 * <p>
030 * Rationale: Instantiating utility classes does not make sense.
031 * A common mistake is forgetting to hide the default constructor.
032 * </p>
033 *
034 * @author lkuehne
035 */
036public class HideUtilityClassConstructorCheck extends Check {
037
038    /**
039     * A key is pointing to the warning message text in "messages.properties"
040     * file.
041     */
042    public static final String MSG_KEY = "hide.utility.class";
043
044    @Override
045    public int[] getDefaultTokens() {
046        return getAcceptableTokens();
047    }
048
049    @Override
050    public int[] getAcceptableTokens() {
051        return new int[] {TokenTypes.CLASS_DEF};
052    }
053
054    @Override
055    public int[] getRequiredTokens() {
056        return getAcceptableTokens();
057    }
058
059    @Override
060    public void visitToken(DetailAST ast) {
061        if (isAbstract(ast)) {
062            // abstract class could not have private constructor
063            return;
064        }
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     * @param ast class definition for check.
094     * @return true if a given class declared as abstract.
095     */
096    private static boolean isAbstract(DetailAST ast) {
097        return ast.findFirstToken(TokenTypes.MODIFIERS)
098            .branchContains(TokenTypes.ABSTRACT);
099    }
100
101    /**
102     * @param ast class definition for check.
103     * @return true if a given class declared as static.
104     */
105    private static boolean isStatic(DetailAST ast) {
106        return ast.findFirstToken(TokenTypes.MODIFIERS)
107            .branchContains(TokenTypes.LITERAL_STATIC);
108    }
109
110    /**
111     * Details of class that are required for validation.
112     */
113    private static class Details {
114        /** Class ast. */
115        private final DetailAST ast;
116        /** Result of details gathering. */
117        private boolean hasMethodOrField;
118        /** Result of details gathering. */
119        private boolean hasNonStaticMethodOrField;
120        /** Result of details gathering. */
121        private boolean hasNonPrivateStaticMethodOrField;
122        /** Result of details gathering. */
123        private boolean hasDefaultCtor;
124        /** Result of details gathering. */
125        private boolean hasPublicCtor;
126
127        /**
128         * C-tor.
129         * @param ast class ast
130         * */
131        Details(DetailAST ast) {
132            this.ast = ast;
133        }
134
135        /**
136         * Getter.
137         * @return boolean
138         */
139        public boolean isHasMethodOrField() {
140            return hasMethodOrField;
141        }
142
143        /**
144         * Getter.
145         * @return boolean
146         */
147        public boolean isHasNonStaticMethodOrField() {
148            return hasNonStaticMethodOrField;
149        }
150
151        /**
152         * Getter.
153         * @return boolean
154         */
155        public boolean isHasNonPrivateStaticMethodOrField() {
156            return hasNonPrivateStaticMethodOrField;
157        }
158
159        /**
160         * Getter.
161         * @return boolean
162         */
163        public boolean isHasDefaultCtor() {
164            return hasDefaultCtor;
165        }
166
167        /**
168         * Getter.
169         * @return boolean
170         */
171        public boolean isHasPublicCtor() {
172            return hasPublicCtor;
173        }
174
175        /**
176         * Main method to gather statistics.
177         */
178        public void invoke() {
179            final DetailAST objBlock = ast.findFirstToken(TokenTypes.OBJBLOCK);
180            hasMethodOrField = false;
181            hasNonStaticMethodOrField = false;
182            hasNonPrivateStaticMethodOrField = false;
183            hasDefaultCtor = true;
184            hasPublicCtor = false;
185            DetailAST child = objBlock.getFirstChild();
186
187            while (child != null) {
188                final int type = child.getType();
189                if (type == TokenTypes.METHOD_DEF
190                        || type == TokenTypes.VARIABLE_DEF) {
191                    hasMethodOrField = true;
192                    final DetailAST modifiers =
193                        child.findFirstToken(TokenTypes.MODIFIERS);
194                    final boolean isStatic =
195                        modifiers.branchContains(TokenTypes.LITERAL_STATIC);
196                    final boolean isPrivate =
197                        modifiers.branchContains(TokenTypes.LITERAL_PRIVATE);
198
199                    if (!isStatic) {
200                        hasNonStaticMethodOrField = true;
201                    }
202                    if (isStatic && !isPrivate) {
203                        hasNonPrivateStaticMethodOrField = true;
204                    }
205                }
206                if (type == TokenTypes.CTOR_DEF) {
207                    hasDefaultCtor = false;
208                    final DetailAST modifiers =
209                        child.findFirstToken(TokenTypes.MODIFIERS);
210                    if (!modifiers.branchContains(TokenTypes.LITERAL_PRIVATE)
211                        && !modifiers.branchContains(TokenTypes.LITERAL_PROTECTED)) {
212                        // treat package visible as public
213                        // for the purpose of this Check
214                        hasPublicCtor = true;
215                    }
216
217                }
218                child = child.getNextSibling();
219            }
220        }
221    }
222}