Java event handler String error

Question

I am trying to make a GUI application where I am using 2-D array registered with an ActionListener. At compile time I am getting a String s = ((Button)o).getLabel(); declaration not valid here. error. In my application if you click the button every "x" label on button should toggle to "o". The code I used is:

from constructor

public ArrayDemo2()
{
    setLayout(new GridLayout(3,3));
    b= new Button[3][3];

    for(int i=0; i<b.length; i++)
    {
        for(int j=0; j<b[i].length; j++)
        {
            if(Math.random() < 0.5) add(b[i][j] = new Button("X"));
            else add(b[i][j] = new Button("O"));
            b[i][j].addActionListener(this);    
        }
    }
    addWindowListener(new WindowAdapter()
    {
        public void windowClosing(WindowEvent e)
        {
            System.exit(0);
        }
    });

    setSize(600,600);
    setVisible(true);

}
    public void actionPerformed(ActionEvent e)
    {
        Object o = e.getSource();
        String s = "";
        if(o instanceof Button)
        {
        s = ((Button)o).getLabel();
        }   
        if(s.equals("X"))
        ((Button)o).setLabel("O");
        else
        ((Button)o).setLabel("X");

    }

As some answers have already shown. Braces solve the compiler issue. In general, always put single line if and while statement in braces. It visually groups the logic and makes easy to avoid adding another line of code and mistakenly thinking it is captured by the the condition. — eclipz905, Nov 21 '14 at 18:51
`if(o instanceof Button) { Button b = (Button) o; b.setLabel( b.getLabel().equals("X") ? "O" : "X" ); }` — , Nov 21 '14 at 20:59

score 0 · Accepted Answer · answered Nov 21 '14 at 18:35

0

You can't declare a new String within an if statement without brackets.

You'd have to write:

if(o instanceof Button) {
    String s = ((Button)o).getLabel();
}

Which doesn't really make sense since the string goes out of scope immediately. What you probably want is something like this:

String s = "";
if(o instanceof Button) {
    s = ((Button)o).getLabel();
}

answered Nov 21 '14 at 18:35

Kevin DiTraglia

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Its not working. It show incompatible type during registering the event – Harpreet Singh Saini Nov 21 '14 at 18:41
Nothing in the code you posted shows any registering of an event, so I'm assuming the problem is in code you haven't posted in the question. This should solve the `declaration is not valid here` error message you asked about. – Kevin DiTraglia Nov 21 '14 at 18:44
The add actionlistener method needs something that implements ActionListener. You are passing `this`, so just add the `implements ActionListener` to your class. – Kevin DiTraglia Nov 21 '14 at 18:54
I am so sorry that was very poor mistake from my side that should have been taken care of. – Harpreet Singh Saini Nov 21 '14 at 18:57

Java event handler String error

1 Answers1