Operator.java

package com.esri.geoevent.processor.cacheawarefieldcalculator.expression;

public abstract class Operator
{
  final boolean leftAssociative;
  final String symbol;
  final int precedence;
  final int operandCount;

  /**
   * Create a new {@link Operator} for two operands
   * 
   * @param symbol
   *          the symbol to be used in expressions to identify this operation
   * @param leftAssociative
   *          true is the operation is left associative
   * @param precedence
   *          the precedence of the operation
   */
  protected Operator(final String symbol, final boolean leftAssociative, final int precedence)
  {
    super();
    this.leftAssociative = leftAssociative;
    this.symbol = symbol;
    this.precedence = precedence;
    this.operandCount = 2;
  }

  /**
   * Create a new {@link Operator}
   * 
   * @param symbol
   *          the symbol to be used in expressions to identify this operation
   * @param leftAssociative
   *          true is the operation is left associative
   * @param precedence
   *          the precedence of the operation
   * @param operandCount
   *          the number of operands of the operation. A value of 1 means the
   *          operation takes one operand. Any other value means the operation
   *          takes 2 arguments.
   */
  protected Operator(final String symbol, final boolean leftAssociative, final int precedence, final int operandCount)
  {
    super();
    this.leftAssociative = leftAssociative;
    this.symbol = symbol;
    this.precedence = precedence;
    this.operandCount = operandCount == 1 ? 1 : 2;
  }

  /**
   * Create a left associative {@link Operator} with precedence value of 1
   * that uses two operands
   * 
   * @param symbol
   *          the {@link String} to use a symbol for this operation
   */
  protected Operator(final String symbol)
  {
    super();
    this.leftAssociative = true;
    this.symbol = symbol;
    this.precedence = 1;
    this.operandCount = 2;
  }

  /**
   * Create a left associative {@link Operator} for two operands
   * 
   * @param symbol
   *          the {@link String} to use a symbol for this operation
   * @param precedence
   *          the precedence of the operation
   */
  protected Operator(final String symbol, final int precedence)
  {
    super();
    this.leftAssociative = true;
    this.symbol = symbol;
    this.precedence = precedence;
    this.operandCount = 2;
  }

  /**
   * Apply the custom operation on the two operands and return the result as an
   * Object An example implementation for a multiplication could look like this:
   * 
   * <pre>
   * <code>{@code}
   *       Object applyOperation(Object[] values) {
   *           return values[0]*values[1];
   *       }
   * </pre>
   * 
   * </code>
   * 
   * @param values
   *          the operands for the operation. If the {@link Operator} uses
   *          only one operand such as a factorial the operation has to be
   *          applied to the first element of the values array. If the
   *          {@link Operator} uses two operands the operation has to be
   *          applied to the first two items in the values array, with special
   *          care given to the operator associativity. The operand to the left
   *          of the symbol is the first element in the array while the operand
   *          to the right is the second element of the array.
   * @return the result of the operation
   */
  protected abstract Object applyOperation(Object[] values);
}