Java: The Calculator program is designed to perform operations on integers. Writ

Question

Java: The Calculator program is designed to perform operations on integers. Write a similar program that can be used to perform operations on decimal numbers. (Note: If division by zero occurs with values of the int data type, the program throws a division by zero exception. However, if you divide a decimal number by zero, Java does not throw the division by zero exception; it returns the answer as infinity. However, if division by zero occurs, your calculator program must output the message ERROR: / by zero.)

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class Calculator extends JFrame implements
ActionListener {
private JTextField displayText = new JTextField(30);
private JButton[] button = new JButton[16];
private String[] keys = {"7", "8", "9", "/",
"4", "5", "6", "*",
"1", "2", "3", "-",
"0", "C", "=", "+"};
private String numStr1 = "";
private String numStr2 = "";
private char op;
private boolean firstInput = true;
public Calculator() {
setTitle("My Calculator");
setSize(230, 200);
Container pane = getContentPane();
pane.setLayout(null);
displayText.setSize(200,30);
displayText.setLocation(10,10);
pane.add(displayText);
int x, y;
x = 10;
y = 40;
for (int ind = 0; ind < 16; ind++) {
button[ind] = new JButton(keys[ind]);
button[ind].addActionListener(this);
button[ind].setSize(50,30);
button[ind].setLocation(x, y);
pane.add(button[ind]);
x = x + 50;
if ((ind + 1) % 4 == 0) {
x = 10;
y = y + 30; } }
this.addWindowListener(new WindowAdapter()
{ public void windowClosing(WindowEvent e)
{ System.exit(0); } } );
setVisible(true); }
public static void main(String[] args)
{ Calculator C = new Calculator(); } }

Explanation / Answer

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

import java.io.*;

public class Calculator extends JFrame implements ActionListener

{

private JTextField displayText = new JTextField(30);

private JButton[] button = new JButton[16];

private String[] keys = {"7", "8", "9", "/",

"4", "5", "6", "*",

"1", "2", "3", "-",

"0", "C", "=", "+"};

private String numStr1 = "";

private String numStr2 = "";

private char op;

private boolean firstInput = true;

public Calculator()

{

setTitle("My Calculator");

setSize(230, 200);

Container pane = getContentPane();

pane.setLayout(null);

displayText.setSize(200, 30);

displayText.setLocation(10, 10);

pane.add(displayText);

int x, y;

x = 10;

y = 40;

for (int ind = 0; ind < 16; ind++)

{

button[ind] = new JButton(keys[ind]);

button[ind].addActionListener(this);

button[ind].setSize(50, 30);

button[ind].setLocation(x, y);

pane.add(button[ind]);

x = x + 50;

if((ind + 1) % 4 == 0)

{

x = 10;

y = y + 30;

}

}

this.addWindowListener(new WindowAdapter()

{

public void windowClosing(WindowEvent e)

{

System.exit(0);

}

}

);

setVisible(true);

setDefaultCloseOperation(EXIT_ON_CLOSE);

}

public void actionPerformed(ActionEvent e)

{

String resultStr; //Step 1

String str = String.valueOf(e.getActionCommand()); //Steps 1 and 2

char ch = str.charAt(0); //Steps 1 and 3

switch (ch) //Step 4

{

case '0': case '1': case '2': //Step 4a

case '3': case '4': case '5':

case '6': case '7': case '8':

case '9': if (firstInput)

{

numStr1 = numStr1 + ch;

displayText.setText(numStr1);

}

else

{

numStr2 = numStr2 + ch;

displayText.setText(numStr2);

}

break;

case '+': case '-': case '*': //Step 4b

case '/': op = ch;

firstInput = false;

break;

case '=': resultStr = evaluate(); //Step 4c

displayText.setText(resultStr);

numStr1 = resultStr;

numStr2 = "";

firstInput = false;

break;

case 'C': displayText.setText(""); //Step 4c

numStr1 = "";

numStr2 = "";

firstInput = true;

}

}

private String evaluate()

{

final char beep = 'u0007';

try

{

int num1 = Integer.parseInt(numStr1);

int num2 = Integer.parseInt(numStr2);

int result = 0;

switch (op)

{

case '+': result = num1 + num2;

break;

case '-': result = num1 - num2;

break;

case '*': result = num1 * num2;

break;

case '/': result = num1 / num2;

}

return String.valueOf(result);

}

catch(ArithmeticException e)

{

System.out.print(beep);

return "E R R O R: " + e.getMessage();

}

catch(NumberFormatException e)

{

System.out.print(beep);

if (numStr1.equals(""))

return "E R R O R: Invalid First Number" ;

else

return "E R R O R: Invalid Second Number" ;

}

catch(Exception e)

{

System.out.print(beep);

return "E R R O R";

}

}

public static void main(String[] args)

{

Calculator C = new Calculator();

}

}

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