This question involves computing an integer based on two input strings. You will write the compute method

of the following Operator class.

public class Operator

$\{$

$/**$ Returns an integer value based on the input string $*/$

public static int transform$($String str$)$

$\{/*$ implementation not shown $*/\}$

$/**$ Returns an integer based on two input strings, as described in part

$($a$)$

$*$ Precondition Precondition: input and op are not null.

$*$ The length of input is even.

$*$ op is either $"$$$$","^^",$ or $"$##$".$

$*/$

public static int compute$($String input, String op$)$

$\{/*$ to be implemented in part $($a$)*/\}$

$//$ There may be variables and methods that are not shown.

$\}$

$($a$)$ Write the compute method of the Operator class. The method calculates an integer value based on an

input string with even length. The first half and the second half of input are transformed into numeric values

by calls to transform. The numeric values are then used in a calculation based on the mathematical operation

represented by the string, op$.$ The method returns the calculated result.

The helper method transform has been provided. The method returns an integer value based on its String

parameter. For example, the method call transform$("$pear$")$ might return the int value $3.$

The mathematical operations represented by op are described in the following table. Assume that value$1$ is

the numeric value obtained by calling transform on the first half of input and value$2$ is the numeric

value obtained by calling transform on the second half of input.

Test Booklet

Mock Exam Part $2$

Page $10$ of $14$ AP Computer Science A

Value of op Mathematical Operation Description

$"$$$$"$ Addition value$1$ plus value$2$

$"^^"$ Multiplication value$1$ times value$2$

$"$##$"$ Subtraction value$1$ minus value$2$

For example, assume that calls to transform are made from the Operator class and that

transform$("$orang$")$ returns $2$ and transform$("$epear$")$ returns $6.$ Then the method call

Operator.compute$("$orangepear$","$$$$")$ should return $8.$

As another example, the method call Operator.compute$("$orangepear$","$##$")$ should return $-4.$

Complete method compute. You must use transform appropriately to receive full credit.

$/**$ Returns an integer based on two input strings, as described in part

$($a$)$

$*$ Precondition Precondition: input and op are not null.

$*$ The length of input is even.

$*$ op is either $"$$$$","^^",$ or $"$##$".$

$*/$

public static int compute$($String input, String op$)$

$($b$)$ A programmer wants to modify the Operator class so that the compute method has a single String

parameter containing both input and op$.$

Write a description of how you would change the Operator class in order to support this modification. Do not

write the program code for this change.

Make sure to include the following in your response.

$$ Identify any new or modified variables or methods.

$$ Describe, for each new or revised variable or method, how it would change or be implemented, including

visibility and type.