cannot instantiate a class using a button

问题

I am trying to make a screen capturing program.

What I have is a transparent window, which will give the area to be captured, with a button capture on it, and I am trying to instantiate a class captureScreen that works good when captureScreen is individually executed using a command prompt

I am trying to instantiate this captureScreen class when button capture is hit.

I have tried keeping this class on my screenrecord.java, putting the code in event listener also. In both these cases,I get these errors

AWTException,must be caught or declared

 Robot robot = new Robot();

and IOException in BufferedImage image line.

And keeping the captureScreen.java separate does nothing.System.out.println("Start"); would even not print anything.

Here is my screenrecord.java code

public class screenrecord extends JFrame implements ActionListener{
    public screenrecord() {...
    }
    public void actionPerformed(ActionEvent e){
        if ("record".equals(e.getActionCommand())) {
            captureScreen a = new captureScreen();
            } 
    }   
}

And captureScreen.java, works fine individually.

public class captureScreen extends Object{

    public static void main(String args[]){
        ...
        Robot robot = new Robot();
        BufferedImage image = robot.createScreenCapture(screenRectangle);
        ImageIO.write(image, "png", new File(filename));
        System.out.println("Done");
    }

}

All your suggestions, comments, advices are welcome and appreciated. Please help me sort this problem. Thanks.

回答1:

You need to be using try/catches. Those aren't errors so much as warnings. For instance, insert this around the code that has the AWTException:

try
{
    //code causing AWTException
    Robot robot = new Robot();
}
catch(AWTException e)
{
    System.out.println("Error"+e);
}

And:

try
{
    //code causing IOException
    BufferedImage image = robot.createScreenCapture(screenRectangle);
}
catch(IOException e)
{
    System.out.println("Error"+e);
}

Or combine both:

try
{
    //code causing AWTException or IOException
    Robot robot = new Robot();
    BufferedImage image = robot.createScreenCapture(screenRectangle);
}
catch(IOException e)
{
    System.out.println("Error"+e);
}
catch(AWTException e)
{
    System.out.println("Error"+e);
}

For further reading, this may help clarify exceptions:

http://docs.oracle.com/javase/tutorial/essential/exceptions/definition.html

回答2:

Works on editing the captureScreen.java as,

public class captureScreen extends Object{

    public captureScreen() {
        ....
        filename = ".\\out.png";
        try{Robot robot = new Robot();
             ............ }
        catch(Exception e)  /* Catch Exceptions too  */
        {
            System.out.println("Error"+e);
        }
    }

    public static void main(String args[]){
        new captureScreen();
    }
}

Use main to instantiate another function.

来源：https://stackoverflow.com/questions/17220399/cannot-instantiate-a-class-using-a-button

标签

java

swing

actionlistener

instantiation

awtrobot