Question

Need help with implementing a While, Do-while and for loops in a program.

UML:

- scnr : Scanner

- rows : int

- MAX_ASCII : int

-------------------------------------------------------------------------------

+ CharacterTables() :

+ CharacterTables(rows : int) :

- getStartingValue() : int

-displayTable(startValue : int) : void

- userContinue() : boolean

+ main(args : String[]) : void

In Section 5.10 we saw that there is a close relationship between char and int. Variables of type char store numbers. (Actually, variables of all types store numbers - that’s what’s in computer storage: 0s and 1s.) In Java, you can do something like this:

char letter = 65;

System.out.println(letter);

and you will see the letter ‘A’ printed. (See Table 5.10.1) On the other hand, you can’t do this:

int x = 65;

char letter = x;             // will cause an error

System.out.println(letter);

because the compiler cannot verify that the x won’t be a value that is out of bounds for a char. But you can force the conversion with a cast (section 5.8) this way:

int x = 65;

char letter = (char) x;

System.out.println(letter);

if you’re sure (like here) that x will be a valid char value.

In this lab, you will print a small table of corresponding int and char values. (See the sample run.)

1. Create a class named CharacterTables as specified in the UML.

2. Create a constant for the max ASCII value (126.)

3. The main method will have only one line:
   new CharacterTables();

4. The no-arg constructor calls the 1 arg constructor with an argument of 10.

5. The 1-arg constructor does the work of the application, calling the three private methods in a loop until the user enters ‘Q’. See the sample run.

6. The getStartingValue method has an endless loop. It prompts for the starting value, which must be between 0 and (MAX_ASCII - rows + 1) so that the table does not extend beyond the ASCII table. Return only when a valid value has been entered.

7. The displayTable method will print the table shown, in a loop. Each row has a number and the corresponding character. The first row will be the user’s number and corresponding letter, the second row will be the number+1, etc.

8. The userContinue method prompts the user to continue or quit. It returns false on entry of ‘Q’ or ‘q’, true otherwise.

9. When a loop is required , you must determine the correct type of loop to use.

10. // Table must be printed using (printf), Only use While, Do-While and For loops in this exercise.

Sample run

User input in bold.

Enter a starting integer between 0 and 117: -1

Enter a starting integer between 0 and 117: 118

Enter a starting integer between 0 and 117: 117

117 u

118 v

119 w

120 x

121 y

122 z

123 {

124 |

125 }

126 ~

Enter C to continue, Q to quit: c

Enter a starting integer between 0 and 117: 61

61 =

62 >

63 ?

64 @

65 A

66 B

67 C

68 D

69 E

70 F

Enter C to continue, Q to quit: q

Answer 1

Source Code in Java:

import java.util.Scanner;
class CharacterTables
{
//class variables
Scanner scnr;
int rows;
final int MAX_ASCII=126; //constant variable to store maximum ASCII value
CharacterTables(int rows) //parametrized constructor
{
this.rows=rows;
scnr=new Scanner(System.in);
}
CharacterTables() //default constructor
{
this(10);
}
int getStartingValue() //method to input starting value till it is valid and return it
{
int startValue;
do
{
System.out.print("Enter a starting integer between 0 and "+(MAX_ASCII-rows+1)+": ");
startValue=scnr.nextInt();
}while(startValue<=0 || startValue>MAX_ASCII-rows+1);
return startValue;
}
void displayTable(int startValue) //method to display a table of characters from a given starting value
{
for(int i=startValue;i<startValue+rows;i++)
{
System.out.printf("%d %c\n",i,i);
}
}
boolean userContinue() //method to accept user choice to continue or not and return a boolean accordingly
{
System.out.print("Enter C to continue, Q to quit: ");
char ch=scnr.next().charAt(0);
if(ch=='q' || ch=='Q')
return false;
return true;
}
public static void main(String args[])
{
//running the methods
CharacterTables ct=new CharacterTables();
do
{
int startValue=ct.getStartingValue();
ct.displayTable(startValue);
}while(ct.userContinue());
}
}

Output: