Программа расчета уравнений - Java-код, использующий строки и конструктор с 4 параметрами. Решатель уравнений с одним шагом с переменной в первом месте

Question

Программа расчета уравнений - оператор switch должен работать, но term1 должен быть переменной (в алгебре), и я не думаю, что код использует его как переменную - следует оценить уравнение в виде x op b = c,где x - любое имя переменной, а b и c - целые числа. Результаты должны отображаться как x op b = c ==> x =

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;

        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
            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);
        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;
            //expand this switch statement to work on all the operators

            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 = a + "= " + (c - b);
            break;

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

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

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

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

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

    public static void main(String args[])
    {

        EquationSolver panel = new EquationSolver();

    }
}