using java textfields

[bravephantom]

In my project "scientific calculator", im using 2 textfields in my GUI app. the problem now (or actually what i dislike) is the user has to use the 2 textfields even if he needs a function of only 1 parameter as trig functions and roots.
when i enter 1 value in the first textfield and leave the other blank, the program doesnt give any output.
Is there any way so i can use only 1 textfield for functions which take 1 parameter?

[SammyB]

You'll need to give us more details. For single operand functions like sin and 1/x, a "normal" calculator would get the single operand from the display and replace the display with the results. For double operand functions like x mod y and x**y, you get the x from the display when the user presses the function button and you get the y from the display when the user presses = and display the results. So, having textfields doesn't make sense.

[bravephantom]

For double operand functions like x mod y and x**y, you get the x from the display when the user presses the function button and you get the y from the display when the user presses = and display the results. So, having textfields doesn't make sense.

first: did u mean i should use a stack so i get the operand (y) which comes immediately before the equal sign and the operand (x) that comes immediately before the operator ??

second: how can i use a textfield more than once instead of having multiple textfields??

[SammyB]

> should use a stack ?
You only need to have a class-level variable for the first operand and get the second operand from the textfield. That's sort of a stack, but a very small one.

> how can i use a textfield more than once
Take a look at the code I wrote for a simple calculator and try to understand it first, then think about how to add some scientific buttons. Notice that when an operator key is first pressed, I get the number from the textfield and store it in dDisplay, then on subsequent operator presses, I combine dDisplay with the current contents of the textfield.

Note, this is just a very simple calculator. If you want to have parentheses keys, then you will have to use a stack and the code will be more confusing.
[code=java]
/*
* Chapter 6: Calculator
* Programmer: Sam Barrett
* Date: 24 Oct 2007
* Filename: Calculator.java
* Purpose: This program creates a calculator with a menu.
* Change Notes: Created an array of 'key caps' to make button creation easier.
* Did all of the button stuff in a single loop.
* Used the first letter of the menu & keys in a single switch statement.
* Corrected the code so that it works like a regular calculator.
* (Their code for = was wrong)
* Made the button font readable and the buttons square.
* Changed some variable names to ones that I liked better.
* Demoted the class-level variables that did not need to be class-level.
* Made it more modular.
*/
import java.awt.*;
import java.awt.datatr ansfer.*;
import java.awt.event. ActionEvent;
import java.awt.event. ActionListener;
import java.awt.event. WindowAdapter;
import java.awt.event. WindowEvent;
import java.text.Decim alFormat;
import javax.swing.JOp tionPane;

public class Calculator extends Frame implements ActionListener
{
private TextField answerField;
private boolean isFirstOperand = true;
private boolean isClearPending = true;
private char cLastOp;
private double dDisplay = 0.0;
private DecimalFormat fmtDisplay = new DecimalFormat(" ########.###### ##");
private String[] sKeyCaps = {"7","8","9" ,"/",
"4","5","6","*" ,
"1","2","3" ,"-",
"0",".","=","+" };
public Calculator()
{
//Create Menu
MenuBar mnuBar = new MenuBar();
this.setMenuBar (mnuBar);
Menu mnuFile = new Menu("File", true);
mnuBar.add(mnuF ile);
MenuItem mnuFileExit = new MenuItem("Exit" );
mnuFileExit.add ActionListener( this);
mnuFile.add(mnu FileExit);
Menu mnuEdit = new Menu("Edit", true);
mnuBar.add(mnuE dit);
MenuItem mnuEditClear = new MenuItem("Clear ");
mnuEditClear.ad dActionListener (this);
mnuEdit.add(mnu EditClear);
MenuItem mnuEditCopy = new MenuItem("Copy" );
mnuEditCopy.add ActionListener( this);
mnuEdit.add(mnu EditCopy);
MenuItem mnuEditPaste = new MenuItem("Paste ");
mnuEditPaste.ad dActionListener (this);
mnuEdit.add(mnu EditPaste);
Menu mnuAbout = new Menu("About", true);
mnuBar.add(mnuA bout);
MenuItem mnuAboutCalc = new MenuItem("About Caculator");
mnuAboutCalc.ad dActionListener (this);
mnuAbout.add(mn uAboutCalc);

//Create Components
answerField = new TextField(20);
answerField.set Editable(false) ;

//Setup Frame & Layouts & buttons
this.setLayout( new BorderLayout()) ;
Panel keysPanel = new Panel();
keysPanel.setLa yout(new GridLayout(4,4, 10,10));
Font f = new Font("Verdana", Font.BOLD, 20);
Button[] keys = new Button[16];
for (int i=0; i<16; i++)
{
keys[i] = new Button(sKeyCaps[i]);
keys[i].setFont(f);
keys[i].addActionListe ner(this);
keysPanel.add(k eys[i]);
}
this.add(answer Field, BorderLayout.NO RTH);
this.add(keysPa nel, BorderLayout.CE NTER);

clearCalculator ();

this.addWindowL istener(
new WindowAdapter()
{
public void windowClosing(W indowEvent e)
{ System.exit(0); }
}
);
}
public void actionPerformed (ActionEvent e)
{
String sItem = e.getActionComm and();
char cFirst = sItem.charAt(0) ;
switch (cFirst)
{
case 'E': // Exit
System.exit(0);
break;
case 'C': // Clear or Copy
if (sItem == "Clear")
clearCalculator ();
else if (sItem == "Copy")
{
Clipboard cb = Toolkit.getDefa ultToolkit().ge tSystemClipboar d();
StringSelection contents = new StringSelection (answerField.ge tText());
cb.setContents( contents, null);
}
break;
case 'P': // Paste
Clipboard cb = Toolkit.getDefa ultToolkit().ge tSystemClipboar d();
Transferable contents = cb.getContents( this);
try
{
String s = (String)content s.getTransferDa ta((DataFlavor. stringFlavor));
answerField.set Text(fmtDisplay .format(Double. parseDouble(s)) );
}
catch (Throwable ex)
{
clearCalculator ();
}
break;
case 'A': // About
JOptionPane.sho wMessageDialog( this,
"Calculator ver. 1.0\nCornerSton e Software\nCopyr ight 2007\nAll rights reserved",
"About Calculator", JOptionPane.INF ORMATION_MESSAG E);
break;
case '0': case '1': case '2': case '3': case '4': case '5': // Numbers
case '6': case '7': case '8': case '9': case '.':
if (isClearPending ) // Start of a new operand
{
answerField.set Text("");
isClearPending = false;
}
answerField.set Text(answerFiel d.getText() + sItem);
break;
case '+': case '-': case '*': case '/': case '=': // Operators
if (isFirstOperand )
processFirstOp( cFirst);
else
processNextOp(c First);
break;
}
}

public void clearCalculator ()
{
isFirstOperand = true;
answerField.set Text("");
answerField.req uestFocus();
}
public void processFirstOp( char cOp)
{
String s = answerField.get Text();
if (s=="")
dDisplay = 0.0;
else
dDisplay = Double.parseDou ble(s);
isClearPending = true;
isFirstOperand = false;
cLastOp = cOp;
}

public void processNextOp(c har cOp)
{
String s = answerField.get Text();
if (s!="")
{
Double d = Double.parseDou ble(s);
switch (cLastOp) // Note, = falls thru: nothing to do but set ClearPending
{
case '+':
dDisplay += d;
break;
case '-':
dDisplay -= d;
break;
case '*':
dDisplay *= d;
break;
case '/':
dDisplay /= d;
break;
}
answerField.set Text(fmtDisplay .format(dDispla y));
isClearPending = true;
}
cLastOp = cOp;
}

public static void main(String[] args)
{
//Setup the frame
Calculator frm = new Calculator();
frm.setTitle("C alculator Application");
frm.setBounds(2 00, 200, 250, 300);
frm.setVisible( true);

//Setup an icon
Image icon = Toolkit.getDefa ultToolkit().ge tImage("calcIma ge.gif");
frm.setIconImag e(icon);
}
}
[/code]