Swing Java Interface Implementation error

Question

My project is supposed to do basic operations on polynomials. Each polynomial si an ArrayList of objects from class Monom. I created an interface with Swing. I made a method that transforms a String received into a Polinom object. If I use basic commands, like when I press a button, get text and show it, everything works fine. But when I call the method mentioned before (toPolinom) , the buttons do not work anymore and red lines are written in the console.

This is how the button code looks like :

 mybutton = new JButton("Suma");
    mybutton.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {

            String pol1 = numberField1.getText();
            String pol2 = numberField2.getText();
            polinom1 = new Polinom(p1);
            polinom2 = new Polinom(p2);
            polinom1 = polinom1.toPolinom(pol1);
            polinom2 = polinom2.toPolinom(pol2);
            resultField.setText(polinom1.suma(polinom1, polinom2)
                    .toString());       

        }
    }); 

   mybutton2 = new JButton("Diferenta");
    mybutton2.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            String pol1 = numberField1.getText();
            String pol2 = numberField2.getText();
            polinom1 = polinom1.toPolinom(pol1);
            polinom2 = polinom2.toPolinom(pol2);
            resultField.setText(rezultat.diferenta(polinom1, polinom2)
                    .toString());

        }
    });

resultField and numberField1 are type JTextField;

This is my toPolinom() method from class Polinom.java:

   public  Polinom toPolinom(String p1) {

    List<Monom> prez = new ArrayList<Monom>();
    int grad, coef;
    int i = 0;
    for(i=0; i<p1.length()-1; i=i+5){
        grad=0; coef=0;
        if(p1.charAt(i)=='+') coef=Character.getNumericValue(p1.charAt(i+1));
        else if (p1.charAt(i)=='-') coef=-Character.getNumericValue(p1.charAt(i+1));
        grad=Character.getNumericValue(p1.charAt(i+4));
        prez.add(new MonomZ(grad, coef));
    }


    return new Polinom(prez);
}

I tested this methode, and it works.

Finally, this is what I receive when I click my buttons :

   Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: -1
at java.util.ArrayList.elementData(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at tema1.Polinom.toString(Polinom.java:208)
at tema1.Fatza$1.actionPerformed(Fatza.java:61)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$400(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

The warning methode added :

  public String toString() {

    String Rezultat = "";
    for (int i = 0; i < polinom.size() - 1; i++) {
        Rezultat = Rezultat + verificare(polinom.get(i), polinom, i);
    }
    return Rezultat
            + verificare(polinom.get(polinom.size() - 1), polinom, //line 208
                    polinom.size() - 1);

}

private String verificare(Monom monom, List<Monom> polinom, int n) {
    // functia verifica daca trebuie adaugat semn sau nu
    String text;
    boolean ok = true;
    for (int i = 0; i < n; i++) {
        if (polinom.get(i).getCoef().doubleValue() != 0) {
            ok = false;
            break;
        }
    }
    double numar = monom.getCoef().doubleValue();
    if (ok == true && numar > 0) {
        text = monom.toString();
    } else {
        text = "+" + monom.toString();
    }
    if (numar < 0) {// numarul are inclus semn negativ
        text = monom.toString();
    }
    return text;
}

If I forgot any information, please ask me.

Don't ignore the exception message as it's telling you what's wrong, an ArrayIndexOutOfBoundsException, what the incorrect value is, -1 and the line number where it occurs: at tema1.Polinom.toString(Polinom.java:208). So what code is on line 208 of the Polinom class? — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Mar 17, 2015 at 19:10
Please show that line of code and the code around it. Edit your question. And it matters little if it's working well anywhere else as it's not working well now. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Mar 17, 2015 at 19:13

Hovercraft Full Of Eels · Accepted Answer · 2015-03-17 19:15:30Z

3

You're calling

verificare(polinom.get(polinom.size() - 1), polinom,' 'polinom.size() - 1);

and getting an ArrayIndexOutOfBoundsException with a -1 value suggesting that your polinom collection's size is 0 when you are getting the error. Check for this, and don't call this method if the size is 0.

answered Mar 17, 2015 at 19:15

Hovercraft Full Of Eels

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2 Comments

Laura D Over a year ago

You are right. If I don't call for this methode in ActionListener, I have no errors. But How come it works in my tests and all the rest? Could you point what I am doing wrong? Thank you

Hovercraft Full Of Eels Over a year ago

@LauraD: for that you would need to create and post a minimal runnable example program or mcve.

Rami.Q · Accepted Answer · 2015-03-17 19:24:05Z

3

in your methode:

public  Polinom toPolinom(String p1) {
    ....
    for(i=0; i<p1.length()-1; i=i+5){

you increment i every loop about 5

so imagine this string "1234567": first loop you get 12345, next loop only 67, but you try to do this:

grad=Character.getNumericValue(p1.charAt(i+4));

at this moment, i+4 = 9, and this is outOfBound... i guess (not tested it, and you don't show the line where the error is) this is your problem

edited Mar 17, 2015 at 19:24

answered Mar 17, 2015 at 19:18

Rami.Q

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2 Comments

Laura D Over a year ago

the thing about toPolinom() is that it is made to only work for particular cases. The user must respect some rules. So my String looks like : +1X^3-2X^0.

JonH Over a year ago

@LauraD In this case your issue is probably from what Hovercraft mentioned as long as you are validating the length of p1. +1 anyhow as this could of been the issue had there been no rules in place to validate p1.Length%5==0

Laura D · Accepted Answer · 2015-03-18 16:38:35Z

Everything worked perfectly after I modified the methods toString() and verificare() as follows:

      public String toString() {
    int ok = 0;
    String Rezultat = "";
    for (int i = 0; i < polinom.size(); i++) {
        Rezultat = Rezultat + verificare(polinom.get(i), polinom, i);
        if (polinom.get(i).getCoef().doubleValue() != 0)
            ok = 1;
    }
    if (ok == 1)
        return Rezultat;
    else
        return "0";

}

private String verificare(Monom monom, List<Monom> polinom, int n) {
    String text = "";

    double numar = monom.getCoef().doubleValue();
    if (n != 0 && numar > 0) {

        text = "+" + monom.toString();
    } else
        text = monom.toString();
    if (numar < 0) {// numarul are inclus semn negativ
        text = monom.toString();
    }
    return text;

}

Thank you very much for all your help!

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