001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2020 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.coding;
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 * <p>
029 * Checks that switch statement has a {@code default} clause.
030 * </p>
031 * <p>
032 * Rationale: It's usually a good idea to introduce a
033 * default case in every switch statement. Even if
034 * the developer is sure that all currently possible
035 * cases are covered, this should be expressed in the
036 * default branch, e.g. by using an assertion. This way
037 * the code is protected against later changes, e.g.
038 * introduction of new types in an enumeration type.
039 * </p>
040 * <p>
041 * To configure the check:
042 * </p>
043 * <pre>
044 * &lt;module name=&quot;MissingSwitchDefault&quot;/&gt;
045 * </pre>
046 * <p>Example of violation:</p>
047 * <pre>
048 * switch (i) {    // violation
049 *  case 1:
050 *    break;
051 *  case 2:
052 *    break;
053 * }
054 * </pre>
055 * <p>Example of correct code:</p>
056 * <pre>
057 * switch (i) {
058 *  case 1:
059 *    break;
060 *  case 2:
061 *    break;
062 *  default: // OK
063 *    break;
064 * }
065 * </pre>
066 * <p>
067 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
068 * </p>
069 * <p>
070 * Violation Message Keys:
071 * </p>
072 * <ul>
073 * <li>
074 * {@code missing.switch.default}
075 * </li>
076 * </ul>
077 *
078 * @since 3.1
079 */
080@StatelessCheck
081public class MissingSwitchDefaultCheck extends AbstractCheck {
082
083    /**
084     * A key is pointing to the warning message text in "messages.properties"
085     * file.
086     */
087    public static final String MSG_KEY = "missing.switch.default";
088
089    @Override
090    public int[] getDefaultTokens() {
091        return getRequiredTokens();
092    }
093
094    @Override
095    public int[] getAcceptableTokens() {
096        return getRequiredTokens();
097    }
098
099    @Override
100    public int[] getRequiredTokens() {
101        return new int[] {TokenTypes.LITERAL_SWITCH};
102    }
103
104    @Override
105    public void visitToken(DetailAST ast) {
106        final DetailAST firstCaseGroupAst = ast.findFirstToken(TokenTypes.CASE_GROUP);
107
108        if (!containsDefaultSwitch(firstCaseGroupAst)) {
109            log(ast, MSG_KEY);
110        }
111    }
112
113    /**
114     * Checks if the case group or its sibling contain the 'default' switch.
115     *
116     * @param caseGroupAst first case group to check.
117     * @return true if 'default' switch found.
118     */
119    private static boolean containsDefaultSwitch(DetailAST caseGroupAst) {
120        DetailAST nextAst = caseGroupAst;
121        boolean found = false;
122
123        while (nextAst != null) {
124            if (nextAst.findFirstToken(TokenTypes.LITERAL_DEFAULT) != null) {
125                found = true;
126                break;
127            }
128
129            nextAst = nextAst.getNextSibling();
130        }
131
132        return found;
133    }
134
135}