It doesn't see my 'if' statements

Discussion in 'Java' started by bilsch, Jun 26, 2012.

  1. bilsch

    bilsch Guest

    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 only
    does addition and subtraction but it doesn't work. A number is
    accumulated in the textbox and when '+' button is clicked the displayed
    string is converted to double, the displayed string remains until the
    first digit of the next number is entered then the first number is
    cleared and the second number begins. When '=' is clicked the second
    displayed string (number) is converted to double and added to the first
    double number. The operation is controlled by 'opFlag' and 'addFlag'
    settings. The problem apparently is that the 'if' statements that set
    the flags are not being executed. I tried NetBeans debugger to watch
    the values but I don't know how to use the debugger well enough. I'm
    hoping someone here can tell me what I'm doing wrong so I can move on.
    Your comments will be appreciated. TIA Bill S.

    THE GUI FILE:

    import java.awt.*;
    import javax.swing.*;

    public class CalcGUIQ2 extends JFrame {
    CrunchQ2 crunchNu = new CrunchQ2(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 one = new JButton("1");
    JButton two = new JButton("2");
    JButton tre = new JButton("3");
    JButton add = new JButton("+");
    JButton sub = new JButton("--");


    JButton zro = new JButton("0");
    JButton dot = new JButton(".");
    JButton equ = new JButton("=");

    public CalcGUIQ2() {
    super();
    setTitle("Calculator");


    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) {
    CalcGUIQ2 frame = new CalcGUIQ2();

    }
    }


    THE CALCULATION FILE:


    import javax.swing.*;
    import java.awt.event.*;

    public class CrunchQ2 implements ActionListener{
    CalcGUIQ2 gui;
    String strng1 = "";
    String noChar = "";
    String nine = "999999999";
    boolean addFlag = false;
    boolean subFlag = false;
    boolean opFlag = false;

    Double operand1 = 0.0;
    Double operand2 = 0.0;
    public CrunchQ2(CalcGUIQ2 in) {
    gui = in;
    }
    public void actionPerformed(ActionEvent event){
    String btn = event.getActionCommand();
    // opflag clears display
    if (opFlag = true){
    gui.number1.setText(noChar);
    opFlag = false;
    }
    if (btn == "=") {
    operand2=Double.parseDouble(strng1);
    if (addFlag = true) {
    operand1 += operand2;
    addFlag = false;
    }
    if (subFlag = true) {
    operand1 -= operand2;
    subFlag = false;
    }
    }
    if (btn == ".") {strng1 += btn;}
    else if (btn == "0") {strng1 += btn;}
    else if (btn == "1") {strng1 += btn;}
    else if (btn == "2") {strng1 += btn;}
    else if (btn == "3") {strng1 += btn;}
    else if (btn == "4") {strng1 += btn;}
    else if (btn == "5") {strng1 += btn;}
    else if (btn == "6") {strng1 += btn;}
    else if (btn == "7") {strng1 += btn;}
    else if (btn == "8") {strng1 += btn;}
    else if (btn == "9") {strng1 += btn;}
    gui.number1.setText(strng1);


    if (btn == "+") {
    addFlag = true;
    opFlag = true;
    operand1=Double.parseDouble(strng1);}

    if (btn == "--") {
    subFlag = true;
    opFlag = true;
    operand1=Double.parseDouble(strng1);}

    }
    }
    bilsch, Jun 26, 2012
    #1
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  2. bilsch

    Lew Guest

    On Tuesday, June 26, 2012 3:52:41 PM UTC-7, markspace wrote:
    > On 6/26/2012 3:49 PM, bilsch wrote:
    >
    > > public void actionPerformed(ActionEvent event){
    > > String btn = event.getActionCommand();
    > > // opflag clears display
    > > if (opFlag = true){

    >
    >
    > This is assignment, not == test. You need two == for equals testing.
    >
    > If you are using NetBeans, it should have flagged this with a warning.
    > Mine does.


    It's also redundant.

    if (opFlag)

    is all you need.

    Otherwise you are either saying 'if (true == true)' which is the exact same logic
    as 'if (true)', or 'if (false == true)', which is the same (almost) as 'if (false)'.

    --
    Lew
    Lew, Jun 27, 2012
    #2
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  3. On Tue, 26 Jun 2012 15:52:41 -0700, markspace wrote:

    > On 6/26/2012 3:49 PM, bilsch wrote:
    >
    >> public void actionPerformed(ActionEvent event){
    >> String btn = event.getActionCommand();
    >> // opflag clears display if (opFlag = true){

    >
    >
    > This is assignment, not == test. You need two == for equals testing.
    >
    > If you are using NetBeans, it should have flagged this with a warning.
    > Mine does.


    As far as I can see the result of your calculation is never written to
    gui.number1


    --
    martin@ | Martin Gregorie
    gregorie. | Essex, UK
    org |
    Martin Gregorie, Jun 27, 2012
    #3
  4. bilsch

    bilsch Guest

    On 6/26/2012 3:52 PM, markspace wrote:
    > On 6/26/2012 3:49 PM, bilsch wrote:
    >
    >> public void actionPerformed(ActionEvent event){
    >> String btn = event.getActionCommand();
    >> // opflag clears display
    >> if (opFlag = true){

    >
    >
    > This is assignment, not == test. You need two == for equals testing.
    >
    > If you are using NetBeans, it should have flagged this with a warning.
    > Mine does.
    >

    Thanks. My stupid mistake. NetBeans doesn't flag it on my system - ???

    I have now fixed those errors and it STILL doesn't work.
    bilsch, Jun 27, 2012
    #4
  5. bilsch

    bilsch Guest

    On 6/26/2012 4:44 PM, Martin Gregorie wrote:
    > On Tue, 26 Jun 2012 15:52:41 -0700, markspace wrote:
    >
    >> On 6/26/2012 3:49 PM, bilsch wrote:
    >>
    >>> public void actionPerformed(ActionEvent event){
    >>> String btn = event.getActionCommand();
    >>> // opflag clears display if (opFlag = true){

    >>
    >>
    >> This is assignment, not == test. You need two == for equals testing.
    >>
    >> If you are using NetBeans, it should have flagged this with a warning.
    >> Mine does.

    >
    > As far as I can see the result of your calculation is never written to
    > gui.number1
    >
    >

    It doesn't go that far. I'm testing for the display to change when the
    second string of digits starts getting entered.
    bilsch, Jun 27, 2012
    #5
  6. bilsch

    bilsch Guest

    On 6/26/2012 4:40 PM, Lew wrote:
    > On Tuesday, June 26, 2012 3:52:41 PM UTC-7, markspace wrote:
    >> On 6/26/2012 3:49 PM, bilsch wrote:
    >>
    >>> public void actionPerformed(ActionEvent event){
    >>> String btn = event.getActionCommand();
    >>> // opflag clears display
    >>> if (opFlag = true){

    >>
    >>
    >> This is assignment, not == test. You need two == for equals testing.
    >>
    >> If you are using NetBeans, it should have flagged this with a warning.
    >> Mine does.

    >
    > It's also redundant.
    >
    > if (opFlag)
    >
    > is all you need.
    >
    > Otherwise you are either saying 'if (true == true)' which is the exact same logic
    > as 'if (true)', or 'if (false == true)', which is the same (almost) as 'if (false)'.
    >

    I changed the opFlag and addFlag statements and it STILL doesn't work.
    TIA Bill S.
    bilsch, Jun 27, 2012
    #6
  7. bilsch

    Mike Winter Guest

    On 27/06/2012 01:22, bilsch wrote:

    >>> On 6/26/2012 3:49 PM, bilsch wrote:
    >>>
    >>>> public void actionPerformed(ActionEvent event){
    >>>> String btn = event.getActionCommand();
    >>>> // opflag clears display
    >>>> if (opFlag = true){


    [snip]

    > I changed the opFlag and addFlag statements and it STILL doesn't work.


    There's also the subFlag condition (and ideally using the equals method
    for comparison as mentioned in <jsd9cf$hha$>), but
    another, significant problem is to do with your program's logic as you
    don't reset the state of the String, strng1, or output the computed value.

    After an addition or subtraction operation, you need to reset your
    string so that you start building the next operand, not a concatenation
    of the first /and/ second operands. You also need to set the JTextField
    text to the (type-converted) value of operand1 when requesting the total.

    Kind regards,
    Mike

    --
    Michael Winter
    Replace ".invalid" with ".uk" to reply by e-mail.
    Mike Winter, Jun 27, 2012
    #7
  8. bilsch

    Roedy Green Guest

    On Tue, 26 Jun 2012 15:49:29 -0700, bilsch <> wrote,
    quoted or indirectly quoted someone who said :

    >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 only
    >does addition and subtraction but it doesn't work. A number is
    >accumulated in the textbox and when '+' button is clicked the displayed
    >string is converted to double, the displayed string remains until the
    >first digit of the next number is entered then the first number is
    >cleared and the second number begins. When '=' is clicked the second
    >displayed string (number) is converted to double and added to the first
    >double number. The operation is controlled by 'opFlag' and 'addFlag'
    >settings. The problem apparently is that the 'if' statements that set
    >the flags are not being executed. I tried NetBeans debugger to watch
    >the values but I don't know how to use the debugger well enough. I'm
    >hoping someone here can tell me what I'm doing wrong so I can move on.
    >Your comments will be appreciated. TIA Bill S.


    I have not studied your program, but it sounds from your general
    complaint like the problem might be you don't understand that nothing
    gets painted until after an event handler returns. You may not
    appreciate why event handlers cannot dither in the least. They have
    to do i tiny bit of work and return, or else they will gum up the
    entire JVM which an only process one Swing event at a time.


    I suggest some background reading on events. e.g.
    http://mindprod.com/jgloss/event11.html
    --
    Roedy Green Canadian Mind Products
    http://mindprod.com
    When you get stuck trying to solve a computer program:
    1. Go into the kitchen and make coffee.
    2. If that fails, go for a walk.
    3. If that fails, take a nap.
    Why? To avoid being swamped with details, to see the big picture,
    to allow in some random noise to kick you out of your thinking rut.
    Roedy Green, Jun 27, 2012
    #8
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