001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2026 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.blocks;
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 * <div>
029 * Finds nested blocks (blocks that are used freely in the code).
030 * </div>
031 *
032 * <p>
033 * Rationale: Nested blocks are often leftovers from the
034 * debugging process, they confuse the reader.
035 * </p>
036 *
037 * <p>
038 * For example, this check finds the obsolete braces in
039 * </p>
040 * {@snippet :
041 * public void guessTheOutput()
042 * {
043 *   int whichIsWhich = 0;
044 *   {
045 *     whichIsWhich = 2;
046 *   }
047 *   System.out.println("value = " + whichIsWhich);
048 * }
049 * }
050 *
051 * <p>
052 * and debugging / refactoring leftovers such as
053 * </p>
054 * {@snippet :
055 * // if (conditionThatIsNotUsedAnyLonger)
056 * {
057 *   System.out.println("unconditional");
058 * }
059 * }
060 *
061 * <p>
062 * A case in a switch statement does not implicitly form a block.
063 * Thus, to be able to introduce local variables that have case scope
064 * it is necessary to open a nested block. This is supported, set
065 * the allowInSwitchCase property to true and include all statements of the case in the block.
066 * </p>
067 *
068 * @since 3.1
069 */
070@StatelessCheck
071public class AvoidNestedBlocksCheck extends AbstractCheck {
072
073    /**
074     * A key is pointing to the warning message text in "messages.properties" file.
075     */
076    public static final String MSG_KEY_BLOCK_NESTED = "block.nested";
077
078    /**
079     * Allow nested blocks if they are the only child of a switch case.
080     */
081    private boolean allowInSwitchCase;
082
083    /**
084     * Creates a new {@code AvoidNestedBlocksCheck} instance.
085     */
086    public AvoidNestedBlocksCheck() {
087        // no code by default
088    }
089
090    @Override
091    public int[] getDefaultTokens() {
092        return getRequiredTokens();
093    }
094
095    @Override
096    public int[] getAcceptableTokens() {
097        return getRequiredTokens();
098    }
099
100    @Override
101    public int[] getRequiredTokens() {
102        return new int[] {TokenTypes.SLIST};
103    }
104
105    @Override
106    public void visitToken(DetailAST ast) {
107        final DetailAST parent = ast.getParent();
108        if (parent.getType() == TokenTypes.SLIST
109                && (!allowInSwitchCase || hasSiblings(ast))) {
110            log(ast, MSG_KEY_BLOCK_NESTED);
111        }
112    }
113
114    /**
115     * Checks whether the AST node has any siblings or not.
116     *
117     * @param ast node to examine
118     * @return {@code true} if the node has one or more siblings
119     */
120    private static boolean hasSiblings(DetailAST ast) {
121        return ast.getPreviousSibling() != null || ast.getNextSibling() != null;
122    }
123
124    /**
125     * Setter to allow nested blocks if they are the only child of a switch case.
126     *
127     * @param allowInSwitchCase whether nested blocks are allowed
128     *                 if they are the only child of a switch case.
129     * @since 3.2
130     */
131    public void setAllowInSwitchCase(boolean allowInSwitchCase) {
132        this.allowInSwitchCase = allowInSwitchCase;
133    }
134
135}