Question

Please help to resolve my error. This Java code is supposed to evaluate one line equation of the form X Operator =Z where X is any name of a variable and Y and Z are integers By user in equation solver window. Currently the code executes expressions such as Y Operator(+,-,*,/) Z

package Equations;

/**
* This program evaluates arithmetic expressions
*/

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.StringTokenizer;

public class EquationSolver extends JFrame
implements ActionListener
{
private JTextField display;

private static final String ARROW = "==> ";

public EquationSolver()
{
super("Equation Solver");
display = new JTextField(40);
display.setFont(new Font("Monospaced", Font.BOLD, 14));
display.setBackground(Color.white);
display.setForeground(Color.blue);
display.addActionListener(this);
display.setText("Enter a math problem to solve");
setBounds(50, 150, 450, 100);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container c = getContentPane();
c.setLayout(new FlowLayout());
c.add(display);

setVisible(true);
// Select the whole display text:
display.selectAll();

// Prepare for typing:
display.requestFocus();
}

public void actionPerformed(ActionEvent e)
{
// Skip if display has any selected text:
if (display.getSelectedText() != null)
return;

String text = display.getText();
display.setText(text + " " + process(text));
display.selectAll();
}

private String process(String s)
{
String term1, op, term2, term3, equals;
equals = "=";

s = s.trim(); //this takes all the white space out on the end

//s.insert(" ",s.indexOf('=')+1);
//s.insert(" ",s.indexOf('=')-1);

//modify s so that there are spaces around the operator and/or equals sign (extra spaces are ok but must have 1 space)
//only works for 3 or 5 tokens in this program(the else part of the if-statement)

StringTokenizer terms = new StringTokenizer(s);

if (terms.countTokens() == 3)
{
term1 = terms.nextToken();
op = terms.nextToken();
term2 = terms.nextToken();
return evaluate(term1, op, term2);
}
else if(terms.countTokens() == 5)
{
term1 = terms.nextToken();
op = terms.nextToken();
term2 = terms.nextToken();
equals = terms.nextToken();
term3 = terms.nextToken();
return evaluate(term1, op, term2, term3);
}
else
return ARROW + "Syntax error";
}

/**
* Evaluates an arithmetic expression in the form
* "a +/- b" and returns the result
* in the form "= c" or an error message.
*/
private String evaluate(String term1, String op, String term2)
//write another method evaluate with 4 parameters for the second part of the problem
{
String result;

if (op.length() != 1)
return ARROW + "Syntax error";

char opSign = op.charAt(0); //why is this at 0?
int a = Integer.parseInt(term1);
int b = Integer.parseInt(term2);

switch (opSign)
{
case '+':
result = "= " + (a + b);
break;

case '-':
result = "= " + (a - b);
break;

case '*':
result = "= " + (a * b);
break;

case '%':
if(b==0)
result = "==> Divide by zero error!";
else // a%b==0
result = "= " + (a / b);
break;
case '/':
if(b==0)
result = "==> Divide by zero error!";
else if(a%b>0)
result = "==> " + a + " is not evenly divisible by " + b;
else //a%b==0
result = "= " + (a / b);
break;

default:
result = ARROW + "Invalid operation";
break;
}
return result;
}

private String evaluate(String term1, String op, String term2, String term3)
{
String result;

if (op.length() != 1)
return ARROW + "Syntax error";

char opSign = op.charAt(0);
int b = Integer.parseInt(term2);
int c = Integer.parseInt(term3);
int a = Integer.parseInt(term1);


switch (opSign)
{
case '+':
result = ARROW + a + "= " + (c - b);
break;

case '-':
result = a + "= " + (c + b);
break;

case '*':
if(b==0)
result = ARROW + "No Solution";
else if(c%b != 0)
result = ARROW + "The answer is not an integer";
else
result = ARROW + a + "= " + (c / b);
break;

case '%': //still needs work
if(b==0)
result = ARROW + "Divide by zero error!";
else // a%b==0
result = JOptionPane.showInputDialog(term1 + " = " + b + "n " + " + " + c + "where n>=0;");
break;

case '/':
if(b==0)
result = ARROW + "Divide by zero error!";
else //a%b==0
result = ARROW + a + "= " + (c * b);
break;

default:
result = ARROW + "Invalid operation";
break;
}
return result;
}

public static void main(String args[])
{

EquationSolver panel = new EquationSolver();

}
}

Answer 1

Modified Program:

/**
* This program evaluates arithmetic expressions
*/

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.StringTokenizer;

public class EquationSolver extends JFrame
implements ActionListener {
private JTextField display;

private static final String ARROW = "==> ";

public EquationSolver() {
super("Equation Solver");
display = new JTextField(40);
display.setFont(new Font("Monospaced", Font.BOLD, 14));
display.setBackground(Color.white);
display.setForeground(Color.blue);
display.addActionListener(this);
display.setText("Enter a math problem to solve");
setBounds(50, 150, 450, 100);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container c = getContentPane();
c.setLayout(new FlowLayout());
c.add(display);

setVisible(true);
// Select the whole display text:
display.selectAll();

// Prepare for typing:
display.requestFocus();
}

public void actionPerformed(ActionEvent e) {
// Skip if display has any selected text:
if (display.getSelectedText() != null)
return;

String text = display.getText();
display.setText(text + " " + process(text));
display.selectAll();
}

private String process(String s) {
String term1, op, term2, term3, equals;
equals = "=";

s = s.trim(); //this takes all the white space out on the end

//s.insert(" ",s.indexOf('=')+1);
//s.insert(" ",s.indexOf('=')-1);

//modify s so that there are spaces around the operator and/or equals sign (extra spaces are ok but must have 1 space)
//only works for 3 or 5 tokens in this program(the else part of the if-statement)

StringTokenizer terms = new StringTokenizer(s, "=+/*-%");
if (terms.countTokens() == 2) {

term1 = terms.nextToken();
if (s.contains("+"))
op = "+";
else if (s.contains("-"))
op = "-";
else if (s.contains("/"))
op = "/";
else if (s.contains("*"))
op = "*";
else if (s.contains("%"))
op = "%";
else return ARROW + "Syntax error";
term2 = terms.nextToken();
return evaluate(term1, op, term2);
} else if (terms.countTokens() == 3) {
term1 = terms.nextToken();
if (s.contains("+"))
op = "+";
else if (s.contains("-"))
op = "-";
else if (s.contains("/"))
op = "/";
else if (s.contains("*"))
op = "*";
else if (s.contains("%"))
op = "%";
else return ARROW + "Syntax error";

term2 = terms.nextToken();
term3 = terms.nextToken();
return evaluate(term1, op, term2, term3);
} else
return ARROW + "Syntax error";
}

/**
* Evaluates an arithmetic expression in the form
* "a +/- b" and returns the result
* in the form "= c" or an error message.
*/
private String evaluate(String term1, String op, String term2)
//write another method evaluate with 4 parameters for the second part of the problem
{
String result;

if (op.length() != 1)
return ARROW + "Syntax error";

char opSign = op.charAt(0); //why is this at 0?
int a = Integer.parseInt(term1);
int b = Integer.parseInt(term2);

switch (opSign) {
case '+':
result = "= " + (a + b);
break;

case '-':
result = "= " + (a - b);
break;

case '*':
result = "= " + (a * b);
break;

case '%':
if (b == 0)
result = "==> Divide by zero error!";
else // a%b==0
result = "= " + (a / b);
break;
case '/':
if (b == 0)
result = "==> Divide by zero error!";
else if (a % b > 0)
result = "==> " + a + " is not evenly divisible by " + b;
else //a%b==0
result = "= " + (a / b);
break;

default:
result = ARROW + "Invalid operation";
break;
}
return result;
}
private String evaluate(String term1, String op, String term2, String term3) {
String result;

char opSign = op.charAt(0);
int b = Integer.parseInt(term2);
int c = Integer.parseInt(term3);

switch (opSign) {
case '+':
result = ARROW + term1 + "= " + (c - b);
break;

case '-':
result = ARROW + term1 + "= " + (c + b);
break;

case '*':
if (b == 0)
result = ARROW + "No Solution";
else if (c % b != 0)
result = ARROW + "The answer is not an integer";
else
result = ARROW + term1 + "= " + (c / b);
break;

case '%': //still needs work
if (b == 0)
result = ARROW + "Divide by zero error!";
else // a%b==0
result = JOptionPane.showInputDialog(term1 + " = " + b + "n " + " + " + c + "where n>=0;");
break;

case '/':
if (b == 0)
result = ARROW + "Divide by zero error!";
else //a%b==0
result = ARROW + term1 + "= " + (c * b);
break;

default:
result = ARROW + "Invalid operation";
break;
}
return result;
}

public static void main(String args[]) {

EquationSolver panel = new EquationSolver();

}
}

Output: