Predicate.java

package simpledb;

/** Predicate compares tuples to a specified Field value.
 */
public class Predicate {

 /** Constants used for return codes in Field.compare */
 public enum Op {
 EQUALS, GREATER_THAN, LESS_THAN, LESS_THAN_OR_EQ, GREATER_THAN_OR_EQ, LIKE, NOT_EQUALS;

 /**
 * Interface to access operations by a string containing an integer
 * index for command-line convenience.
 *
 * @param s a string containing a valid integer Op index
 */
 public static Op getOp(String s) {
 return getOp(Integer.parseInt(s));
 }

 /**
 * Interface to access operations by integer value for command-line
 * convenience.
 *
 * @param i a valid integer Op index
 */
 public static Op getOp(int i) {
 return values()[i];
 }
 }
 
	protected int field;
	
 protected Op op;
 
 protected Field operand;

 /**
 * Constructor.
 *
 * @param field field number of passed in tuples to compare against.
 * @param op operation to use for comparison
 * @param operand field value to compare passed in tuples to
 */
 public Predicate(int field, Op op, Field operand) {
 	this.field = field;
 	this.op = op;
 	this.operand = operand;
 }

 /**
 * Compares the field number of t specified in the constructor to the
 * operand field specified in the constructor using the operator specific
 * in the constructor. The comparison can be made through Field's
 * compare method.
 *
 * @param t The tuple to compare against
 * @return true if the comparison is true, false otherwise.
 */
 public boolean filter(Tuple t) {
 	Field f = t.getField (field);
 	if (f != null)
 		return f.compare(op, operand);
 return false;
 }

 /**
 * Returns something useful, like
 * "f = this.fieldid op = this.opstring operand = this.operandstring
 */
 public String toString() {
 	return String.format("f = %i op = %s operand = %s", field, op, operand);
 }
}