ArithmeticExpression


1   package com.calipso.reportgenerator.reportcalculator.arithmetic;
2   
3   import java.util.Map  ;
4   import java.util.Collection  ;
5   import java.io.Serializable  ;
6   
7   /**
8    * Resuelve expressiones aritmeticas
9    */
10  
11  public abstract class ArithmeticExpression implements Serializable  {
12  
13    /**
14     * Retorna el resultado para la expresion que recibe
15     * por parametro.
16     * @param expression
17     * @return
18     */
19    public static ArithmeticExpression newFrom(String   expression) {
20      String   exp = prepareExpression(expression);
21      Object  [] tokens = getTokens(exp);
22      if (tokens.length == 1) {
23        return ValueArithmeticExp.newValueExpFrom(prepareExpression(tokens[0].toString()));
24      } else {
25        ArithmeticExpression subExp1 = ArithmeticExpression.newFrom(tokens[0].toString());
26        ArithmeticExpression subExp2 = ArithmeticExpression.newFrom(tokens[2].toString());
27        return OperationArithmeticExp.newOperationFrom(subExp1, tokens[1].toString(), subExp2);
28      }
29    }
30  
31    /**
32     * Prepara una expression previamente a ser resuelta.
33     * @param expression
34     * @return
35     */
36    private static String   prepareExpression(String   expression) {
37      String   exp = expression.trim();
38      if (exp.charAt(0) == '(' && exp.charAt(exp.length() - 1) == ')') {
39        if(!(exp.indexOf(")") < exp.indexOf("(", 1))){
40          return exp.substring(1, exp.length() - 1);
41        }
42      }
43      return exp;
44    }
45  
46    /**
47     * Devuelve el indice del operador primario de la expresion
48     * @param expression
49     * @return
50     */
51    private static int indexOfOperator(String   expression) {
52      int index = -1;
53      int alternateIndex = -1;
54      int parenthesis = 0;
55      for (int i = 0; i < expression.length(); i++) {
56        char current = expression.charAt(i);
57        if (current == '(') {
58          parenthesis++;
59        } else {
60          if (current == ')') {
61            parenthesis--;
62          } else {
63            if ((parenthesis == 0)) {
64              if (current == '+' || current == '-') {
65                index = i;
66                break;
67              } else {
68                if (current == '*' || current == '/') {
69                  alternateIndex = i;
70                }
71              }
72            }
73          }
74        }
75      }
76      if (index == -1) {
77        index = alternateIndex;
78      }
79      return index;
80    }
81  
82    /**
83     * En base al indice del operador primario parte en dos
84     * la expresion, ubica cada porcion en un array de 3 posiciones
85     * siendo la posicion del medio la que contiene el operador
86     * primario y retorna dicho array.
87     * @param expression
88     * @return
89     */
90    private static Object  [] getTokens(String   expression) {
91      int index = indexOfOperator(expression);
92      if (index == -1) {
93        return new Object  []{expression};
94      } else {
95        Object  [] array = new Object  [3];
96        array[0] = expression.substring(0, index);
97        array[1] = expression.substring(index, index +1);
98        array[2] = expression.substring(index + 1);
99        return array;
100     }
101   }
102 
103   public abstract float value(Map   context);
104 
105   public void getVariables(Collection   variables) {
106     //Do nothing
107   }
108 }
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