The document presents a Java program using the Scanner class to create a transaction menu allowing users to process yogurt purchases and manage stamps. It includes symbolic constants for various options and prompts the user to purchase yogurt or shut down the program, while handling user input and displaying results. Additionally, it includes error handling for invalid inputs and manages the logic for redeeming free yogurt based on earned stamps.

2. Using Scanner class in Java
This class transaction is displaying a menu and accepting values in
different formats using scanner class methods.
import java.util.Scanner;
public class Transaction
{
public static void main(String[] args) {
// symbolic constants
final int FREE_YOGURT_STAMPS = 7;
final char PURCHASE_OPTION = 'p';
final char STOP_OPTION = 's';
final char YES_OPTION = 'y';
final char NO_OPTION = 'n';
final String MENU = "Menu:n P (process Purchase)n S (Shut
down)nn Your choice: ";
final String INVALID_CHOICE = "n *** Use P or S, please.
***n";
final String PROMPT_AWARD = "nYou qualify for a free yogurt.
Would you like to use your credits? (Y or N)";
final String PROMPT_NUM_YOGURT = "nHow many yogurts would you
like to buy? ";
final String EARN_STAMPS = "n You just earned %d stamps and
have a total of %d to use.nn";
final String USE_STAMPS = "nYou have just used %d stamps and
have a total of %d to use.nEnjoy your free yogurt.nn";
final String INVALID_RESP = "n *** Invalid response ***n";
Scanner in = new Scanner(System.in);
// number of stamps of the single customer
int stamps = 0;
// the main loop, stop until user entered s
while (true) {
System.out.print(MENU);
String line = in.nextLine().trim(); // read one line
if (line.length() > 0) {

3. // check the first letter
char first = line.charAt(0);
first = Character.toLowerCase(first); // convert to
lower case
if (first == STOP_OPTION) {
// first letter is an upper or lower case 's'
// break the loop to end the program
break;
}
if (first == PURCHASE_OPTION) {
// the operators choose purchase
if (stamps >= FREE_YOGURT_STAMPS) {
// ask the customer to choose award
transaction
System.out.println(PROMPT_AWARD);
// check the first letter
line = in.nextLine().trim();
if (line.length() > 0) {
first = line.charAt(0);
first = Character.toLowerCase(first); //
convert to lower case
if (first == YES_OPTION) {
stamps = stamps - FREE_YOGURT_STAMPS;
System.out.printf(USE_STAMPS,
FREE_YOGURT_STAMPS, stamps);
continue;
} else if (first == NO_OPTION) {
// flow down to the normal transaction
} else {
// invalid option
System.out.println(INVALID_RESP);
continue;
}
}
}
// normal transaction
System.out.println(PROMPT_NUM_YOGURT);
int num = in.nextInt();
in.nextLine(); // ignore the n in the line
if (num >= 0) {
stamps = stamps + num;
System.out.printf(EARN_STAMPS, num, stamps);
} else {
// invalid number
System.out.println(INVALID_RESP);
}
continue;
}
}

4. // otherwise, invalid input
System.out.println(INVALID_CHOICE);
}
}
}