Re: I need a different approach - suggestions please
On 6/27/2012 6:54 PM, Lew wrote:
bilsch wrote:
Lew wrote:
There are a few mistakes in your code.
You don't need to call 'super()' in the constructor explicitly.
That's what happens by default anyway.
You called the constructor directly from the 'main()' routine. That means
you called it from the primary thread of the program. You don't know this
yet, probably, unless you've already studied concurrency in Java a little bit.
The problem is that the GUI won't work right if you do that. You have to
move GUI actions onto the "Event Dispatch Thread" (EDT), a background
thread that the system creates to handle all GUI actions.
Also, you start all the action from the constructor. That's bad. As its name
implies, a constructor's purpose is to _construct_ an object, not run its logic.
Run the logic after construction completes and the instance is no longer in a
partially-built state.
And make your indentation consistent with the Java coding conventions (available
on line).
So all together, you'd do something like:
public static void main(String[] arguments) {
java.awt.EventQueue.invokeAndWait( new Runnable() {
@Override public void run() {
CalcGUIQ1 calculator = new CalcGUIQ1();
calculator.setVisible(true);
}
});
}
With help I've gotten some errors out of the program but I have reached
a point where something just won't work how it should. Your comments
What doesn't work, and how should it?
here lead me to believe the reason is the basic way I have things laid
out. But I don't know how to:
> move GUI actions onto the "Event Dispatch Thread" (EDT), further I
dont know how to write an EDT, or what specifically are 'GUI actions' as
opposed to other lines that relate to the GUI.
You don't write the EDT. Did you read the tutorial link I provided?
<http://docs.oracle.com/javase/tutorial/uiswing/concurrency/index.html>
GUI actions are all things that happen on the GUI, such as creating
a 'JFrame', calling 'pack()', playing with 'Graphics', or anything else that
is part of the GUI. Non-GUI actions are things like writing files, calculating
values, updating the logical model, or anything else that is not part of
the GUI.
Do please read the tutorial to which I linked. There's a reason I provided
that link.
Also, I thought the stuff I have in the constructor belonged there.
Not all of it. The program itself must run from a *completely*
constructed object. You start the program from inside the
constructor, therefore it is running on an *incompletely*
constructed object.
I dont know where to call the constructor from if not from 'main'.
You should call the constructor from 'main()', provided you properly
guard it inside the 'invokeAndWait()' call.
Why did you think I recommended otherwise?
I did some reading about threads being unsafe.
It would be very helpful to me if you could show how to rearrange the
code like you say would be better. If you have the time, it would be
very helpful. Thanks.
What was wrong with what I already showed you (and you quoted)?
I looked at the link when you provided it. It said dont read this until
you first read the basic stuff about concurrence in previous topics. I
read that stuff.
Here's the code that should work but doesnt. A stripped down version of
my program is in the 2 files copied below. It is a simple calculator
like in Windows accessories. The example below only does addition and
subtraction. It isn't completely written - never writes the answer to
the textbox I haven't got that far yet. The code below is supposed to
work as follows: A number is sent to the textbox using button clicks and
when '+' button is clicked the displayed string is converted to double.
The displayed string remains displayed until the first digit of the next
number is entered then the displayed string is cleared and the second
number begins in the display. When '=' is clicked the second displayed
number (actually a string) is converted to double and added to the first
double number. The operation should be controlled by the 'opFlag' and
'addFlag' settings. It should clear the textbox when the second number
is entered but it does not. Print statements are included to show
variable values.
THE GUI FILE:
import java.awt.*;
import javax.swing.*;
public class KalcGUI extends JFrame {
Krunch crunchNu = new Krunch(this);
// set up row 1
JPanel row1 = new JPanel();
JTextField number1 = new JTextField(30);
// set up row 2
JPanel row2 = new JPanel();
JButton sev = new JButton("7");
JButton ate = new JButton("8");
JButton nin = new JButton("9");
JButton fou = new JButton("4");
JButton fiv = new JButton("5");
JButton six = new JButton("6");
JButton b04 = new JButton("");
JButton one = new JButton("1");
JButton two = new JButton("2");
JButton tre = new JButton("3");
JButton zro = new JButton("0");
JButton dot = new JButton(".");
JButton equ = new JButton("=");
JButton add = new JButton("+");
JButton sub = new JButton("--");
public KalcGUI() {
super();
setTitle("Calculator");
//setLookAndFeel();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
GridLayout layout = new GridLayout(2, 1, 10, 10);
setLayout(layout);
//add listeners
dot.addActionListener(crunchNu);
zro.addActionListener(crunchNu);
one.addActionListener(crunchNu);
two.addActionListener(crunchNu);
tre.addActionListener(crunchNu);
fou.addActionListener(crunchNu);
fiv.addActionListener(crunchNu);
six.addActionListener(crunchNu);
sev.addActionListener(crunchNu);
ate.addActionListener(crunchNu);
nin.addActionListener(crunchNu);
equ.addActionListener(crunchNu);
add.addActionListener(crunchNu);
sub.addActionListener(crunchNu);
FlowLayout layout1 = new FlowLayout(FlowLayout.CENTER, 10, 10);
row1.add(number1);
row1.setLayout(layout1);
add(row1);
GridLayout layout2 = new GridLayout(5, 3, 10, 10);
row2.setLayout(layout2);
row2.add (sev);
row2.add (ate);
row2.add (nin);
row2.add (fou);
row2.add (fiv);
row2.add (six);
row2.add (one);
row2.add (two);
row2.add (tre);
row2.add (zro);
row2.add (dot);
row2.add (equ);
row2.add (add);
row2.add (sub);
add(row2);
pack();
setVisible(true);
}
public static void main(String[] arguments) {
KalcGUI frame = new KalcGUI();
}
}
THE CALCULATION FILE:
import javax.swing.*;
import java.awt.event.*;
public class Krunch implements ActionListener{
KalcGUI gui;
String strng1 = "";
boolean invFlag = false;
boolean addFlag = false;
boolean subFlag = false;
boolean opFlag = false;
int neg = 0;
String noChar = "";
Double operand1 = 0.0;
Double operand2 = 0.0;
public Krunch(KalcGUI in) {
gui = in;
}
public void actionPerformed(ActionEvent event){
//String strng1 = "";
String btn = event.getActionCommand();
// opflag clears display
if (opFlag){
System.out.println(opFlag);
// THIS SHOULD CLEAR THE TEXTBOX //
gui.number1.setText(noChar);
opFlag = false;
}
if (btn == "=") {operand2=Double.parseDouble(strng1);
if (addFlag) {
operand1 += operand2;
addFlag = false;
}
if (subFlag) {
operand1 += operand2;
subFlag = false;
}
}
if( btn.equals( "1" ) || btn.equals( "2" ) || btn.equals( "3" )
|| btn.equals( "4" )
|| btn.equals( "5" ) || btn.equals( "6" ) ||
btn.equals( "7" ) || btn.equals( "8" )
|| btn.equals( "9" ) || btn.equals( "0" ) ||
btn.equals( "." )) {
strng1 += btn;
}
gui.number1.setText(strng1);
if (btn == "+") {
addFlag = true;
opFlag = true;
System.out.println(addFlag);
System.out.println(opFlag);
operand1=Double.parseDouble(strng1);}
if (btn == "--") {
subFlag = true;
opFlag = true;
operand1=Double.parseDouble(strng1);}
}
}