A single class consisting of multiple methods is used to demonstrate the robustness of keyboard input in Java. A try-catch block is used. The program graphically prints out a square root table by using JTextArea, JScrollPane and JOptionPane.

package robustinput;
import javax.swing.JScrollPane;
import javax.swing.JOptionPane;
import javax.swing.JTextArea;
import java.text.DecimalFormat;
public class RobustInput
{
public static void main(String args[])
{
int inum = 0;
String typeErr = "That is not an integer.";
String rangeErr = "That number is out of range.";
boolean badType;
boolean badRange;
do
{
badType = false;
badRange = false;
try
{
inum = Integer.parseInt(JOptionPane.showInputDialog(null,
"Enter Positive Integer"));
}
catch (NumberFormatException e)
{
badType = true;
inum = 1;
}
if ((inum < 1) || (inum > 150)) badRange = true;
if (badType) JOptionPane.showMessageDialog(null, typeErr,
"Invalid",JOptionPane.ERROR_MESSAGE);
if (badRange) JOptionPane.showMessageDialog(null, rangeErr,
"Invalid",JOptionPane.ERROR_MESSAGE);
} while (badType || badRange);
System.out.println("\n\n\tYou entered: " + inum);
JTextArea outputArea = new JTextArea();
outputArea.append(" i\t Sqrt(i) \n_____________________\n");
DecimalFormat dec4 = new DecimalFormat("0.0000");
for (int i = 1; i <= inum; i++)
{
outputArea.append("\n ");
if (i < 10) outputArea.append("00");
else if (i < 100) outputArea.append("0");
outputArea.append(i + "\t");
if (i < 100) outputArea.append("0");
outputArea.append(dec4.format(Math.sqrt((double)i)));
}
// JOptionPane.showMessageDialog(null, outputArea, "Square Root Table",
JOptionPane.INFORMATION_MESSAGE);
JScrollPane scroller = new JScrollPane(outputArea);
JOptionPane.showMessageDialog(null, scroller, "Square Root Table",
JOptionPane.INFORMATION_MESSAGE);
}
}

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