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1   package net.sourceforge.pmd.rules;
2   
3   import java.util.HashMap;
4   import java.util.Map;
5   import java.util.Set;
6   
7   import net.sourceforge.pmd.AbstractJavaRule;
8   import net.sourceforge.pmd.ast.ASTLocalVariableDeclaration;
9   import net.sourceforge.pmd.ast.ASTStatementExpression;
10  import net.sourceforge.pmd.ast.ASTType;
11  import net.sourceforge.pmd.ast.ASTVariableDeclaratorId;
12  import net.sourceforge.pmd.ast.Node;
13  import net.sourceforge.pmd.ast.SimpleNode;
14  import net.sourceforge.pmd.symboltable.NameOccurrence;
15  import net.sourceforge.pmd.util.CollectionUtil;
16  
17  /**
18   * An operation on an Immutable object (String, BigDecimal or BigInteger) won't change
19   * the object itself. The result of the operation is a new object. Therefore,
20   * ignoring the operation result is an error.
21   */
22  public class UselessOperationOnImmutable extends AbstractJavaRule {
23  
24      /**
25       * These are the BigDecimal methods which are immutable
26       */
27      private static final Set<String> decMethods = CollectionUtil.asSet(new String[] { ".abs", ".add", ".divide", ".divideToIntegralValue", ".max", ".min", ".movePointLeft", ".movePointRight", ".multiply", ".negate", ".plus", ".pow", ".remainder", ".round", ".scaleByPowerOfTen", ".setScale", ".stripTrailingZeros", ".subtract", ".ulp" });
28  
29      /**
30       * These are the BigInteger methods which are immutable
31       */
32      private static final Set<String> intMethods = CollectionUtil.asSet(new String[] { ".abs", ".add", ".and", ".andNot", ".clearBit", ".divide", ".flipBit", ".gcd", ".max", ".min", ".mod", ".modInverse", ".modPow", ".multiply", ".negate", ".nextProbablePrine", ".not", ".or", ".pow", ".remainder", ".setBit", ".shiftLeft", ".shiftRight", ".subtract", ".xor" });
33  
34      /**
35       * These are the String methods which are immutable
36       */
37      private static final Set<String> strMethods = CollectionUtil.asSet(new String[] { ".concat", ".intern", ".replace", ".replaceAll", ".replaceFirst", ".substring", ".toLowerCase", ".toString", ".toUpperCase", ".trim" });
38  
39      /**
40       * These are the classes that the rule can apply to
41       */
42      private static final Map<String, Set<String>> mapClasses = new HashMap<String, Set<String>>();
43      static {
44          mapClasses.put("java.math.BigDecimal", decMethods);
45          mapClasses.put("BigDecimal", decMethods);
46          mapClasses.put("java.math.BigInteger", intMethods);
47          mapClasses.put("BigInteger", intMethods);
48          mapClasses.put("java.lang.String", strMethods);
49          mapClasses.put("String", strMethods);
50      }
51  
52      public Object visit(ASTLocalVariableDeclaration node, Object data) {
53  
54          ASTVariableDeclaratorId var = getDeclaration(node);
55          if (var == null) {
56              return super.visit(node, data);
57          }
58          String variableName = var.getImage();
59          for (NameOccurrence no: var.getUsages()) {
60              // FIXME - getUsages will return everything with the same name as the variable, 
61              // see JUnit test, case 6. Changing to SimpleNode below, revisit when getUsages is fixed
62              SimpleNode sn = no.getLocation();
63              Node primaryExpression = sn.jjtGetParent().jjtGetParent();
64              Class<? extends Node> parentClass = primaryExpression.jjtGetParent().getClass();
65              if (parentClass.equals(ASTStatementExpression.class)) {
66                  String methodCall = sn.getImage().substring(variableName.length());
67                  ASTType nodeType = node.getTypeNode();
68                  if ( nodeType != null ) {
69                      if ( mapClasses.get(nodeType.getTypeImage()).contains(methodCall)) {
70                          addViolation(data, sn);
71                      }
72                  }
73              }
74          }
75          return super.visit(node, data);
76      }
77  
78      /**
79       * This method checks the variable declaration if it is on a class we care
80       * about. If it is, it returns the DeclaratorId
81       * 
82       * @param node
83       *            The ASTLocalVariableDeclaration which is a problem
84       * @return ASTVariableDeclaratorId
85       */
86      private ASTVariableDeclaratorId getDeclaration(ASTLocalVariableDeclaration node) {
87          ASTType type = node.getTypeNode();
88          if (mapClasses.keySet().contains(type.getTypeImage())) {
89              return node.findChildrenOfType(ASTVariableDeclaratorId.class).get(0);
90          }
91          return null;
92      }
93  }