Cannot resolve Varibles

[Bob Dundy]

I have followed the instructions in creating this quadratic program, but I keep getting these compiler errors:
Error: cannot resolve symbol
symbol : variable A
location: class Quadratic
Error: cannot resolve symbol
symbol : variable B
location: class Quadratic
Error: cannot resolve symbol
symbol : variable C
location: class Quadratic
here is the code:

import java.awt.Graphics;
import javax.swing.*;
public class Quadratic extends JApplet {
  double root1;
  double root2;
  
  public static void main( String args[] )
  {
    String firstNumber;     //first value entered, A
    String secondNumber;    //second value entered, B
    String thirdNumber;     //third value entered, C
        
    int A;
    int B;
    int C;
    double root1;
    double root2;
    
    //Obtain values from user
    firstNumber = JOptionPane.showInputDialog( "Solving AX^2 + BX + C, enter A:" );
    secondNumber = JOptionPane.showInputDialog( "Solving AX^2 + BX + C, enter B:" );
    thirdNumber = JOptionPane.showInputDialog( "Solving AX^2 + BX + C, enter C:" );
        
    //Convert numbers from type string to type integer
    A = Integer.parseInt( firstNumber );
    B = Integer.parseInt( secondNumber );
    C = Integer.parseInt( thirdNumber );
    
    //Solving the Quadratic Eqution 
    root1 = ( (double)-B + ( Math.sqrt(Math.pow(B, 2) + ( 4 * A * C ) ) ) ) / ( 2 * A );
    root2 = ( (double)-B - ( Math.sqrt(Math.pow(B, 2) + ( 4 * A * C ) ) ) ) / ( 2 * A );
  
  }//End Method Main
  
  public void paint( Graphics g )
  {
    super.paint( g );
    
    //Draw Rectangle starting at (15, 10), with width 300 pixels, and height 60 pixels
    g.drawRect( 0, 0, 300, 60 );
    
    g.drawString( "Solving " +A +"X^2 + " +B +"X " +C +" = 0", 25, 15 );
    g.drawString( "Root 1 = " + root1, 25, 30 );
    g.drawString( "Root 2 = " + root2, 25, 45);
    
  }//end method paint
  
}//end class Quadratic  

The errors says line 50, which is the g.drawString( "Solving " +A .....
Please help.

[Dirk Schreckmann]

Welcome to JavaRanch, Bob!
The variable A declared in the main method is not available in another method. In other words, variables local to a method are not accessible from another method.
Perhaps you want A to be an instance variable - declared outside of any method.
Getting any ideas?

[Ernest Friedman-Hill]

Hi Bob,
Welcome to JavaRanch!
The variables A, B, and C are defined inside the method main(). That means, by default, that they're only available inside main(). If you try to use them in paint(), as you do here, the compiler will complain that it doesn't know which A, B, and C you mean, since there are none that apply during paint().
There are a couple of ways to exchange information between methods. One way is by passing the variables as arguments -- just as you pass the string firstNumber to the Integer.parseInt() method, you could imaging passing A, B, and C to paint().
Unfortunately, in this case, paint() doesn't accept any int arguments, so that isn't going to work here. What you could do instead is make A, B, and C into static variables defined in the scope of the class itself, not inside main(). Such variables would be useable by all the methods in the class.

public class Quadratic extends JApplet {
  static int A, B, C;
  ...

And remove the definitions inside main().

[Bob Dundy]

Thanks guys, now I understand my mistake
I have to define the local variable so that it is not only in one method.

[Layne Lund]

If it's not in a method, then it is no longer local. Such a variable is called an "instance" variable because each instance of the class gets its own copy of the variable.
Layne

[Ernest Friedman-Hill]

Originally posted by Layne Lund:
Such a variable is called an "instance" variable...

Unless they're static, as they'll need to be here, in which case they're called "static variables" or "class variables."

[Layne Lund]

Point