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package simpledb;

import java.io.Serializable;

/**

* Predicate compares tuples to a specified Field value.

*/

public class Predicate implements Serializable {

int p_field;

Op p_op;

Field p_operand;

private static final long serialVersionUID = 1L;

/** Constants used for return codes in Field.compare */

public enum Op implements Serializable {

EQUALS, GREATER_THAN, LESS_THAN, LESS_THAN_OR_EQ, GREATER_THAN_OR_EQ, LIKE, NOT_EQUALS;

/**

* 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];

}

public String toString() {

if (this == EQUALS)

return "=";

if (this == GREATER_THAN)

return ">";

if (this == LESS_THAN)

return "<";

if (this == LESS_THAN_OR_EQ)

return "<=";

if (this == GREATER_THAN_OR_EQ)

return ">=";

if (this == LIKE)

return "LIKE";

if (this == NOT_EQUALS)

return "<>";

throw new IllegalStateException("impossible to reach here");

}

}

/**

* 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) {

// some code goes here

p_field = field;

p_op = op;

p_operand = operand;

}

/**

* @return the field number

*/

public int getField()

{

// some code goes here

return p_field;

}

/**

* @return the operator

*/

public Op getOp()

{

// some code goes here

return p_op;

}

/**

* @return the operand

*/

public Field getOperand()

{

// some code goes here

return p_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) {

// some code goes here

Field to_compare = t.getField(p_field);

boolean result = to_compare.compare(p_op, p_operand);

return result;

}

/**

* Returns something useful, like "f = field_id op = op_string operand =

* operand_string

*/

public String toString() {

// some code goes here

String output = "";

//f = field_id op = op_string operand =

output = "f: " + p_field;

output = "; op: " + p_op;

output = "; operand: " + p_operand;

return output;

}

}