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1   ////////////////////////////////////////////////////////////////////////////////
2   // checkstyle: Checks Java source code for adherence to a set of rules.
3   // Copyright (C) 2001-2017 the original author or authors.
4   //
5   // This library is free software; you can redistribute it and/or
6   // modify it under the terms of the GNU Lesser General Public
7   // License as published by the Free Software Foundation; either
8   // version 2.1 of the License, or (at your option) any later version.
9   //
10  // This library is distributed in the hope that it will be useful,
11  // but WITHOUT ANY WARRANTY; without even the implied warranty of
12  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13  // Lesser General Public License for more details.
14  //
15  // You should have received a copy of the GNU Lesser General Public
16  // License along with this library; if not, write to the Free Software
17  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
18  ////////////////////////////////////////////////////////////////////////////////
19  
20  package com.puppycrawl.tools.checkstyle.checks.coding;
21  
22  import antlr.collections.AST;
23  import com.puppycrawl.tools.checkstyle.StatelessCheck;
24  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
25  import com.puppycrawl.tools.checkstyle.api.DetailAST;
26  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
27  
28  /**
29   * <p>Checks that string literals are not used with
30   * {@code ==} or {@code &#33;=}.
31   * </p>
32   * <p>
33   * Rationale: Novice Java programmers often use code like
34   * {@code if (x == &quot;something&quot;)} when they mean
35   * {@code if (&quot;something&quot;.equals(x))}.
36   * </p>
37   *
38   * @author Lars K&uuml;hne
39   */
40  @StatelessCheck
41  public class StringLiteralEqualityCheck extends AbstractCheck {
42  
43      /**
44       * A key is pointing to the warning message text in "messages.properties"
45       * file.
46       */
47      public static final String MSG_KEY = "string.literal.equality";
48  
49      @Override
50      public int[] getDefaultTokens() {
51          return getRequiredTokens();
52      }
53  
54      @Override
55      public int[] getAcceptableTokens() {
56          return getRequiredTokens();
57      }
58  
59      @Override
60      public int[] getRequiredTokens() {
61          return new int[] {TokenTypes.EQUAL, TokenTypes.NOT_EQUAL};
62      }
63  
64      @Override
65      public void visitToken(DetailAST ast) {
66          // no need to check for nulls here, == and != always have two children
67          final AST firstChild = ast.getFirstChild();
68          final AST secondChild = firstChild.getNextSibling();
69  
70          if (firstChild.getType() == TokenTypes.STRING_LITERAL
71                  || secondChild.getType() == TokenTypes.STRING_LITERAL) {
72              log(ast.getLineNo(), ast.getColumnNo(),
73                      MSG_KEY, ast.getText());
74          }
75      }
76  }