How do you get the screen width in java?

java.awt.Toolkit.getDefaultToolkit().getScreenSize()

Here are the two methods I use, which account for multiple monitors and task-bar insets. If you don't need the two methods separately, you can, of course, avoid getting the graphics config twice.

static public Rectangle getScreenBounds(Window wnd) {
    Rectangle                           sb;
    Insets                              si=getScreenInsets(wnd);

    if(wnd==null) { 
        sb=GraphicsEnvironment
           .getLocalGraphicsEnvironment()
           .getDefaultScreenDevice()
           .getDefaultConfiguration()
           .getBounds(); 
        }
    else { 
        sb=wnd
           .getGraphicsConfiguration()
           .getBounds(); 
        }

    sb.x     +=si.left;
    sb.y     +=si.top;
    sb.width -=si.left+si.right;
    sb.height-=si.top+si.bottom;
    return sb;
    }

static public Insets getScreenInsets(Window wnd) {
    Insets                              si;

    if(wnd==null) { 
        si=Toolkit.getDefaultToolkit().getScreenInsets(GraphicsEnvironment
           .getLocalGraphicsEnvironment()
           .getDefaultScreenDevice()
           .getDefaultConfiguration()); 
        }
    else { 
        si=wnd.getToolkit().getScreenInsets(wnd.getGraphicsConfiguration()); 
        }
    return si;
    }

The following code should do it (haven't tried it):

GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice gd = ge.getDefaultScreenDevice();
gd.getDefaultConfiguration().getBounds().getWidth();

edit:

For multiple monitors you should use the following code (taken from the javadoc of java.awt.GraphicsConfiguration:

  Rectangle virtualBounds = new Rectangle();
  GraphicsEnvironment ge = GraphicsEnvironment.
          getLocalGraphicsEnvironment();
  GraphicsDevice[] gs =
          ge.getScreenDevices();
  for (int j = 0; j < gs.length; j++) { 
      GraphicsDevice gd = gs[j];
      GraphicsConfiguration[] gc =
          gd.getConfigurations();
      for (int i=0; i < gc.length; i++) {
          virtualBounds =
              virtualBounds.union(gc[i].getBounds());
      }
  } 

Toolkit has a number of classes that would help:

1. getScreenSize - raw screen size
2. getScreenInsets - gets size of toolbar, dock
3. getScreenResolution - dpi

We end up using 1 and 2, to compute usable maximum window size. To get the relevant GraphicsConfiguration, we use

GraphicsEnvironment.getLocalGraphicsEnvironment().getScreenDevices()[0].getDefaultConfiguration();

but there may be smarter multiple-monitor solutions.

The OP probably wanted something like this:

Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();

Toolkit.getDefaultToolkit().getScreenSize().getWidth()

You can get it by using the AWT Toolkit.

Toolkit.getScreenSize().

Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();