Perhaps there are some mistakes but it isn't important, I can fix it myself later. I only don't know how:
1. Send variables a, b, c from the first class to the second class
2. Create a command on the button bt that will draw the graph from the second class in the new window

Oh, and I said that i need graph a*x*x + b*x + c, and in the program is a* sin(b*x + c), but nevermind that


Code:
 import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;



public class mmm extends JFrame implements ActionListener
{
    private final int length = 600;
    private final int height = 400;
    private JTextArea ta;
    private JButton bt;
    private Container c1;
    
   public mmm()
    {
        setSize (length, height);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setTitle("Test");
                
        c1 = getContentPane();
        c1.setLayout(null);
       
        
        ta = new JTextArea();
        ta.setSize(sirina - 100, visina - 100);
        ta.setLocation(1,1);
        c1.add(ta); 
        
        bt = new JButton();
        bt.setLocation(sirina - 80, 50);
        bt.setSize(60, 20);
        bt.addActionListener(this);
        bt.setText("U redu");
        c1.add(bt);
               
    
        setVisible(true);
    }
    
    
    
    public void get_a_b_c()
    {
        String tmp = ta.getText();
        String a1 = "";
        String b1 = "";
        String c1 = "";
        String g = "";
        
        boolean u1 = true;
        boolean u2 = true;
        boolean bo = true;
        for (int i = 0; i < tmp.length(); i++)
        {
            String z = tmp.substring(i, i+1);
            if (((u1 == true) && (u2 == true)) && ((z.equals("0")) || (z.equals("1")) || (z.equals("2")) || (z.equals("3")) || (z.equals("4")) || (z.equals("5")) || (z.equals("6")) || (z.equals("7")) || (z.equals("8")) || (z.equals("9")))) 
                a1 = a1 + z;
            if ((z.equals(",")) && (u1 == false))
                u2 = false;
            if ((z.equals(",")) && (u1 == true))
                u1 = false;
            if (((u1 == false) && (u2 == true)) && ((z.equals("0")) || (z.equals("1")) || (z.equals("2")) || (z.equals("3")) || (z.equals("4")) || (z.equals("5")) || (z.equals("6")) || (z.equals("7")) || (z.equals("8")) || (z.equals("9"))))  
                b1 = b1 + z;
            if (((u1 == false) && (u2 == false)) && ((z.equals("0")) || (z.equals("1")) || (z.equals("2")) || (z.equals("3")) || (z.equals("4")) || (z.equals("5")) || (z.equals("6")) || (z.equals("7")) || (z.equals("8")) || (z.equals("9"))))  
                c1 = c1 + z;
            bo = ((z.equals(",")) || (z.equals("0")) || (z.equals("1")) || (z.equals("2")) || (z.equals("3")) || (z.equals("4")) || (z.equals("5")) || (z.equals("6")) || (z.equals("7")) || (z.equals("8")) || (z.equals("9")));
            if (bo == false)
                g = "greska!!";
        }
        if (g.equals("greska!!"))
        {
            JOptionPane.showMessageDialog (this, "Error!", "Error", JOptionPane.ERROR_MESSAGE);
        }
        
        int a = Integer.parseInt(a1);
        int b = Integer.parseInt(b1);
        int c = Integer.parseInt(c1); 
    
        
    }
    
    
    
                
    public void actionPerformed(ActionEvent e)
    {

        
        if (e.getSource().equals(bt))
      
        // Here should be the command that draws graph
        
  }
    
    public static void main(String[] s)
    {
        mmm m = new mmm();
    }
    
}
Code:
import javax.swing.*;
import java.awt.*;

public class test2 extends JFrame
{
    private final int length = 640, height = 480;
 
    public test2()
    {
        
        setTitle ("Graph of function f (x) = " + a + " sin (" + b + " x + " + c + ")");
        
        setSize (length, height);
        setDefaultCloseOperation (EXIT_ON_CLOSE);
        setBackground (Color.white);
        setVisible (true);
    }
    private void xos (Graphics g)
    {
        g.setColor (Color.blue);
        g.drawLine (0, height / 2, length, height / 2);
        for (int i = 1; i < length/ 20; i++)
        g.drawLine (i * 20, height / 2 - 2, i * 20, height / 2 + 2);
    }
    private void yos (Graphics g)
    {
        g.setColor (Color.blue);
        g.drawLine (length / 2, 0, length / 2, height);
        for (int i = 1; i < height / 20; i++)
        g.drawLine (length / 2 - 2, i * 20, length / 2 + 2, i * 20);
    }
    public void crtaj (Graphics g)
    {
        double x = - length / 40.0, xs = length / 2.0, ys = height / 2.0, y;
        int xp, yp;
        g.setColor (Color.red);
        while (x < length / 40)
        {
            y = a * x*x + b * x + c;
            xp = (int)(xs + 20 * x);
            yp = (int)(ys - 20 * y);
            g.drawOval (xp, yp, 1, 1);
            x += 0.05;
        }
    }
    public void paint (Graphics g)
    {
        xos (g);
        yos (g);
        crtaj (g);
    }
    
    public static void main (String[] s)
    {
        test2 t2 = new test2 (3,3,3);
    }   
}