giáo trình Java By Example phần 5

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giáo trình Java By Example phần 5 Table 17.2 Commonly Used FontMetrics Methods. Method Description Returns the width of a character. charWidth() Returns the fonts ascent. getAscent() Returns the fonts descent. getDescent() Returns the associated Font object. getFont() Returns the fonts height. getHeight() Returns the fonts leading (line spacing). getLeading() Returns the width of a string. stringWidth() Returns a string of information about the font. toString() NOTE If you havent used fonts before, some of the terms-leading, ascent, and descent-used in Table 17.2 may be unfamiliar to you. Leading (pronounced ledding) is the amount of white space between lines of text. Ascent is the height of a character, from the baseline to the top of the character. Descent is the size of the area that accommodates the descending portions of letters, such as the tail on a lowercase g. Height is the sum of ascent, descent, and leading. See Figure 17.3 for examples of each.Figure 17.3 : Ascent, descent, and leading determine the overall height of a font.Example: Displaying Font MetricsMost of the methods listed in Table 17.2 are self-explanatory. However, you probably want a chance tosee them in action. Listing 17.3 is the source code for the MetricsApplet, and Listing 17.4 is the appletsHTML document. When you run the MetricsApplet applet, you see the window shown in Figure 17.4. Atthe top of the window is a text box into which you can enter different strings of text. When you pressEnter, the applet displays the length of the string in pixels. Immediately below the text box is informationabout the current font.Figure 17.4 : This is Appletviewer running the MetricsApplet applet. Listing 17.3 MetricsApplet.java: An Applet That Displays Text Metrics. import java.awt.*; import java.applet.*; http://www.ngohaianh.infopublic class MetricsApplet extends Applet{ TextField textField; public void init() { textField = new TextField(20); add(textField); textField.setText(Default string); } public void paint(Graphics g) { Font font = getFont(); FontMetrics fontMetrics = g.getFontMetrics(font); int n = fontMetrics.getLeading(); String leading = String.valueOf(n); n = fontMetrics.getAscent(); String ascent = String.valueOf(n); n = fontMetrics.getDescent(); String descent = String.valueOf(n); n = fontMetrics.getHeight(); String height = String.valueOf(n); http://www.ngohaianh.info String s = textField.getText(); n = fontMetrics.stringWidth(s); String width = String.valueOf(n); g.drawString(FONT INFO:, 55, 60); g.drawString(Leading: + leading, 70, 80); g.drawString(Ascent: + ascent, 70, 95); g.drawString(Descent: + descent, 70, 110); g.drawString(Height: + height, 70, 125); g.drawString(STRING INFO:, 55, 155); g.drawString(Width: + width, 70, 175); } public boolean action(Event event, Object arg) { repaint(); return true; }}Listing 17.4 METRICSAPPLET.htmL: MetricsApplets HTML Document. http://www.ngohaianh.info Applet Test Page Applet Test Page NOTE Because all of the applets youve written so far in this book havent used text metrics when displaying text, you may wonder why you even need to bother with this stuff. Chances are that when youre running your applets under Windows 95 using the default font, everything will work fine. But remember that your applets may run on machines using other operating systems, and their default fonts may not be exactly the same size. Also, when you create your own fonts, you may not know the resultant fonts size exactly. In order to position text accurately, you need to use font metrics, as youll see later in this chapter.Creating FontsYou may thi ...