ch17.htm

Java_by_Example,初级经典例子哦,珍藏版本

<PRE>

g.setFont(font);

</PRE>

</BLOCKQUOTE>

<P>

At this point, the next text you display in your applet will use

the new font. However, although you request a certain type and

size of font, you can't be sure of what you'll get. The system

tries its best to match the requested font, but you still need

to know at least the size of the font with which you ended up.

You can get all the information you need by creating a <TT>FontMetrics</TT>

object, like this:

<BLOCKQUOTE>

<PRE>

FontMetrics fontMetrics = g.getFontMetrics(font);

</PRE>

</BLOCKQUOTE>

<P>

To get the height of a line of text, call the <TT>FontMetrics</TT>

object's <TT>getHeight()</TT> method, like this:

<BLOCKQUOTE>

<PRE>

int height = fontMetrics.getHeight();<BR>

</PRE>

</BLOCKQUOTE>

<P>

<CENTER>

<TABLE BORDER=1 WIDTH=80%>

<TR VALIGN=TOP><TD><B>CAUTION</B></TD></TR>

<TR VALIGN=TOP><TD>

<BLOCKQUOTE>

When creating a font, be aware that the user's system may not have a particular font loaded. In that case, Java chooses a default font as a replacement. This possible font substitution is a good reason to use methods like <TT>Font.getName()</TT> in order to see whether you got the font you wanted. You especially need to know the size of the font, so you can be sure to position your text lines properly.

</BLOCKQUOTE>



</TD></TR>

</TABLE>

</CENTER>

<P>

<H3><A NAME="ExampleDisplayingDifferentSizedFonts">

Example: Displaying Different Sized Fonts</A></H3>

<P>

You wouldn't create a font unless you had some text to display.

The problem is that before you can display your text, you need

to know at least the height of the font. Failure to consider the

font's height may give you text lines that overlap or that are

spaced too far apart. You can use the height returned from the

<TT>FontMetrics</TT> class's <TT>getHeight()</TT> method as a

row increment value for each line of text you need to print. Listing

17.5, which is the source code for the FontApplet2 applet, shows

how this is done. Listing 17.6 is the applet's HTML document,

and Figure 17.5 shows what the applet looks like.

<P>

<A HREF="f17-5.gif"><B> Figure 17.5 : </B><I>This is Appletviewer running the FontApplet2 applet.



</I></A><P>

<HR>

<BLOCKQUOTE>

<B>Listing 17.5&nbsp;&nbsp;FontApplet2.java: Displaying Different

Sized Fonts.<BR>

</B>

</BLOCKQUOTE>

<BLOCKQUOTE>

<PRE>

import java.awt.*;

import java.applet.*;



public class FontApplet2 extends Applet

{

    TextField textField;



    public void init()

    {

        textField = new TextField(10);

        add(textField);

        textField.setText(&quot;32&quot;);

    }



    public void paint(Graphics g)

    {

        String s = textField.getText();

        int height = Integer.parseInt(s);



        Font font = new Font(&quot;TimesRoman&quot;, Font.PLAIN, height);

        g.setFont(font);

        FontMetrics fontMetrics = g.getFontMetrics(font);

        height = fontMetrics.getHeight();



        int row = 80;

        g.drawString(&quot;This is the first line.&quot;, 70, row);

        row += height;

        g.drawString(&quot;This is the second line.&quot;, 70, row);

        row += height;

        g.drawString(&quot;This is the third line.&quot;, 70, row);

        row += height;

        g.drawString(&quot;This is the fourth line.&quot;, 70, row);

    }



    public boolean action(Event event, Object arg)

    {

        repaint();

        return true;

    }

}

</PRE>

</BLOCKQUOTE>

<HR>

<HR>

<BLOCKQUOTE>

<B>Listing 17.6&nbsp;&nbsp;FONTAPPLET2.htmL: FontApplet2's HTML

Document.<BR>

</B>

</BLOCKQUOTE>

<BLOCKQUOTE>

<PRE>

&lt;title&gt;Applet Test Page&lt;/title&gt;

&lt;h1&gt;Applet Test Page&lt;/h1&gt;

&lt;applet

    code=&quot;FontApplet2.class&quot;

    width=400

    height=200

    name=&quot;FontApplet2&quot;&gt;

&lt;/applet&gt;

</PRE>

</BLOCKQUOTE>

<HR>

<P>

When you run FontApplet2, you see the window shown in Figure 17.5.

The size of the active font is shown in the text box at the top

of the applet, and a sample of the font appears below the text

box. To change the size of the font, type a new value into the

text box and press Enter. Figure 17.6, for example, shows the

applet displaying 12-point font, whereas Figure 17.7 is the applet

displaying 120-point characters. As you can see, no matter what

font size you choose, the lines are properly spaced (although

large fonts overrun the boundaries of the applet's canvas).

<P>

<A HREF="f17-6.gif"><B> Figure 17.6 : </B><I>FontApplet2 can display any size characters you like. This is 12-point text.



</I></A><P>

<P>

<A HREF="f17-7.gif"><B> Figure 17.7 : </B><I>This is FontApplet2 displaying 120-point text.



</I></A><P>

<P>

The spacing of the lines is accomplished by first creating a variable

to hold the vertical position for the next line of text:

<BLOCKQUOTE>

<PRE>

int row = 80;

</PRE>

</BLOCKQUOTE>

<P>

Here, the program not only declares the <TT>row</TT> variable,

but also initializes it with the vertical position of the first

row of text.

<P>

The applet then prints the first text line, using <TT>row</TT>

for <TT>drawString()</TT>'s third argument:

<BLOCKQUOTE>

<PRE>

g.drawString(&quot;This is the first line.&quot;, 70, row);

</PRE>

</BLOCKQUOTE>

<P>

In preparation for printing the next line of text, the program

adds the font's height to the <TT>row</TT> variable:

<BLOCKQUOTE>

<PRE>

row += height;

</PRE>

</BLOCKQUOTE>

<P>

Each line of text is printed, with <TT>row</TT> being incremented

by the font's height in between, like this:

<BLOCKQUOTE>

<PRE>

g.drawString(&quot;This is the second line.&quot;, 70, row);

row += height;

g.drawString(&quot;This is the third line.&quot;, 70, row);

</PRE>

</BLOCKQUOTE>

<H2><A NAME="Summary"><FONT SIZE=5 COLOR=#Ff0000>

Summary</FONT></A></H2>

<P>

In regular Windows programming, creating and using fonts is a

meticulous and frustrating experience. Java, however, simplifies

this task by offering the <TT>Font</TT> and <TT>FontMetrics</TT>

classes. With just a few method calls, you can create the fonts

you need for your applet. Displaying text with any font is as

easy setting the font as the current font and getting the font's

size. The font's height is especially important because a font's

height determines the line spacing you must use. After you've

created and set the font, any text you display will use the new

font.

<H2><A NAME="ReviewQuestions"><FONT SIZE=5 COLOR=#Ff0000>

Review Questions</FONT></A></H2>

<OL>

<LI>What method of the <TT>Graphics</TT> class do you call to

get the active font?

<LI>What method of the <TT>Font</TT> class do you call to get

a font's name?

<LI>What method of the <TT>Font</TT> class do you call to get

a font's height?

<LI>Why is it important to determine the height of the current

font?

<LI>How do you get a reference to a <TT>FontMetrics</TT> object?

<LI>When would you use a <TT>FontMetrics</TT> object to obtain

information about a font instead of using the <TT>Font</TT> object?

<LI>How can you determine the width of an entire text string?

<LI>When referring to fonts, what is a point?

<LI>Define the terms ascent, descent, baseline, and leading.

<LI>How does a font's height relate to ascent, descent, and leading?

<LI>How do you create and use a new font?

<LI>What happens if the font you request is not available on the

user's system?

</OL>

<H2><A NAME="ReviewExercises"><FONT SIZE=5 COLOR=#Ff0000>

Review Exercises</FONT></A></H2>

<OL>

<LI>Write an applet that displays three lines of text using the

16-point Helvetica font. Use the height returned from the <TT>Font</TT>

class's <TT>getHeight()</TT> method to space your lines of text.

<LI>Modify the applet you created in exercise 1 to display bold

text.

<LI>Modify exercise 2's applet so that it uses a <TT>FontMetric</TT>

object to determine the font's height.

<LI>Write an applet called FontApplet3 that provides a button

that the user can click in order to switch between the Courier,

TimesRoman, and Helvetica fonts. The final applet should look

like Figure 17.8, displaying the text using the selected font

with a height of 32 points and using the bold style. Figure 17.9

shows what the applet looks like when the user has clicked the

button and switched to the TimesRoman font. (You can find the

solution to this problem in the CHAP17 folder of this book's CD-ROM.

</OL>

<P>

<A HREF="f17-8.gif"><B> Figure 17.8 : </B><I>This is FontApplet3 displaying the Courier font.

</I></A><P>

<A HREF="f17-9.gif"><B> Figure 17.9 : </B><I>Here's FontApplet3 displaying the TimesRoman font.

</I></A><P>



<HR>











<HR WIDTH="100%"></P></CENTER>

<!-- reference library footer #1-->
</CENTER>
<IMG SRC="/images/rule.gif" WIDTH="460" HEIGHT="5" VSPACE="5"
ALT="Ruler image"><br>

<FONT SIZE="-1">

Contact <a href="mailto:[e-mail]">
[e-mail]</a> with questions or comments.<br>


<a href="/legal/">
Copyright 1998</a> 
<a href="http://www.earthweb.com" target="_top">
EarthWeb Inc.</a>,  All rights reserved.<BR>
PLEASE READ THE <a href="/reference/usage.html">ACCEPTABLE USAGE STATEMENT</a>.
<BR>
Copyright 1998 Macmillan Computer Publishing. All rights reserved.
</FONT>
</BLOCKQUOTE>


<!--outer table--><TD VALIGN="TOP">

<!--right side ads -->
<a target="resource window" href="http://adserver.developer.com/cgi-bin/accipiter/adclick.exe/AREA=DCAD1.REF" alt="Click here for more info"><img src="http://adserver.developer.com/cgi-bin/accipiter/adserver.exe/AREA=DCAD1.REF" alt="Click here for more info" height="88" width="88" border="0"></a>
<P>
<a target="resource window" href="http://adserver.developer.com/cgi-bin/accipiter/adclick.exe/AREA=DCAD2.REF" alt="Click here for more info"><img src="http://adserver.developer.com/cgi-bin/accipiter/adserver.exe/AREA=DCAD2.REF" alt="Click here for more info" height="88" width="88" border="0"></a>
<P>



</td>
</tr>
</table>
</BODY>
</HTML>