1. Examples of class: Using System.in.read ()
Instructor: Mainak Chaudhuri

2. Building a wrapper public class MyInput { // Read a character
public char ReadChar () throws java.io.IOException {
return (char)System.in.read (); }
// Read multiple characters
public String ReadString (int howmany) throws java.io.IOException {
String str = “”;
int k;
for (k=0; k<howmany; k++) {
str += (char)System.in.read ();
return str;

3. Building a wrapper // Read a line
public String ReadLine () throws java.io.IOException {
String str = “”;
char c;
while ((c=(char)System.in.read ()) != ‘\n’) {
str += c; }
return str;

4. Building a wrapper // Read an integer
public int ReadInt () throws java.io.IOException {
String str = “”;
char c;
while (true) {
c = (char)System.in.read ();
if ((c == ‘\n’) || (c == ‘ ‘)) {
break; }
str += c;
Integer n = new Integer (str.trim());
return n.intValue();

5. Building a wrapper // Read a double
public double ReadDouble () throws java.io.IOException {
String str = “”;
char c;
while (true) {
c = (char)System.in.read ();
if ((c == ‘\n’) || (c == ‘ ‘)) {
break; }
str += c;
Double n = new Double (str.trim());
return n.doubleValue();

6. Building a wrapper // Read a float
public float ReadFloat () java.io.IOException {
String str = “”;
char c;
while (true) {
c = (char)System.in.read ();
if ((c == ‘\n’) || (c == ‘ ‘)) {
break; }
str += c;
Float n = new Float (str.trim());
return n.floatValue();
} // end class

7. Using the wrapper Let us build an interactive calculator
Asks for two numbers (integers, floats, or doubles)
Asks for the operation type: +, -, /, *
Computes the answer, prints it, and prompts for the next input
User should be asked before closing the calculator
I leave it to you to extend it further with other complex operations

8. Using the wrapper class DeskCalculator {
public static void main (String a[]) throws java.io.IOException {
char inputOp, exitChar, sundries;
MyInput inp = new MyInput();
double operand1, operand2;
while (true) {
System.out.println (“Enter two numbers:”);
operand1 = inp.ReadDouble ();
operand2 = inp.ReadDouble ();
System.out.print (“What do you want to do? (+, -, *, /)”);
inputOp = inp.ReadChar (); // next slide

9. Using the wrapper // Eat up the \n at the end
sundries = inp.ReadChar ();
switch (inputOp) {
case ‘+’ :
System.out.println (operand1+operand2);
break;
case ‘-’ :
System.out.println (operand1-operand2);
// next slide

10. Using the wrapper case ‘*’ : System.out.println(operand1*operand2);
break;
case ‘/’ :
System.out.println(operand1/operand2);
default :
System.out.println (“Invalid operation!”);
} // end switch

11. Using the wrapper System.out.print (“Want to exit? (y/n)”);
exitChar = inp.ReadChar ();
// Eat up the ‘\n’
sundries = inp.ReadChar ();
if (exitChar == ‘y’) {
System.out.println (“Bye for now!”);
break; }
} // end while
} // end main
} // end class

12. Announcements Lab today for Thursday batch (B1/B2)
Notes on classes and objects in CopyPoint
Extra class on 12th November 1400 to 1615 in L7
Project progress report due on 1st November after class
Two pages
A convincing executive summary of progress (one page)
Future plans with clearly defined deadlines (one page)