java语言程序设计-基础篇--第八版--英文课件(第17章).pptVIP

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * JTextArea If you want to let the user enter multiple lines of text, you cannot use text fields unless you create several of them. The solution is to use JTextArea, which enables the user to enter multiple lines of text. * JTextArea Constructors JTextArea(int rows, int columns) Creates a text area with the specified number of rows and columns. JTextArea(String s, int rows, int columns) Creates a text area with the initial text andthe number of rows and columns specified. * JTextArea Properties text editable columns lineWrap wrapStyleWord rows lineCount tabSize * Example: Using Text Areas This example gives a program that displays an image in a label, a title in a label, and a text in a text area. * Example, cont. * Run TextAreaDemo JComboBox A combo box is a simple list of items from which the user can choose. It performs basically the same function as a list, but can get only one value. * JComboBox Methods To add an item to a JComboBox jcbo, use jcbo.addItem(Object item) To get an item from JComboBox jcbo, use jcbo.getItem() * Using theitemStateChanged Handler public void itemStateChanged(ItemEvent e) { // Make sure the source is a combo box if (e.getSource() instanceof JComboBox) String s = (String)e.getItem(); } * When a choice is checked or unchecked, itemStateChanged() for ItemEvent is invoked as well as the actionPerformed() handler for ActionEvent. Example: Using Combo Boxes This example lets users view an image and a description of a countrys flag by selecting the country from a combo box. * Run ComboBoxDemo JList A list is a component that performs basically the same function as a combo box, but it enables the user to choose a single value or multiple values. * JList Constructors JList() Creates an empty list. JList(Object[] stringItems) Creates a new list initialized with items. * JList Properties selectedIndexd selectedIndices selectedValue sel