Monday, September 17th, 2007
GridBagLayout, a Java layout manager, to position the components in the applet window. GridBagLayout is flexible and offers us a quick way of producing an attractive interface. Listing 4.3 Setting up the user interface. public void init() { QueryField.setEditable(true); OutputField.setEditable(false); NameField.setEditable(true); DBurl.setEditable(true); // We want to set the individual TextArea and TextField to be editable so // the user can edit the OutputField, where we plan on showing the // results of the query. GridBagLayout gridbag = new GridBagLayout(); GridBagConstraints Con = new GridBagConstraints(); // create a new instance of GridBagLayout and the complementary // GridBagConstraints. setLayout(gridbag); // Set the layout of the applet to the gridbag that we created above. setFont(new Font(”Helvetica”, Font.PLAIN, 12)); setBackground(Color.gray); // Set the font and color of the applet. Con.weightx=1.0; Con.weighty=0.0; Con.anchor = GridBagConstraints.CENTER; Con.fill = GridBagConstraints.NONE; Con.gridwidth = GridBagConstraints.REMAINDER; This code requires some explanation. The weightx and weighty properties determine how the space in the respective direction is distributed. If either weight property is set to 0, the default, any extra space is distributed around the outside of the components in the corresponding direction. The components are also centered automatically in that direction. If either weight property is set to 1, any extra space is distributed within the spaces between components in the corresponding direction. Hence, in setting the weightx=1, we have told the GridBagLayout layout manager to position the components on each row so that extra space is added equally between the components on that row. However, the rows of components are vertically clumped together because the weighty property is set to 0.0. Later on, we ll change weighty to 1 so that the large TextArea (the OutputField) takes up extra space equal to all the components added before it. Take a look at Figure 4.3, shown at the end of the chapter, to see what I mean. We also set the anchor property to tell the GridBagLayout to position the components on the center, relative to each other. The fill property is set to NONE so that the components are not stretched to fill empty space. You will find this technique to be useful when you want a large graphics area (Canvas) to take up any empty space that is available around it, respective to the other components. The gridwidth is set to
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