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<a href="http://www.bruceeckel.com/javabook.html">Bruce Eckel's Thinking in Java</a>
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<H2 ALIGN=LEFT>
Drop-down
lists
</H2>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Like
a group of radio buttons, a <A NAME="Index1646"></A><A NAME="Index1647"></A><A NAME="Index1648"></A>drop-down
list is a way to force the user to select only one element from a group of
possibilities. However, it&#8217;s a much more compact way to accomplish this,
and it&#8217;s easier to change the elements of the list without surprising the
user. (You can change radio buttons dynamically, but that tends to be visibly
jarring).
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Java&#8217;s
<A NAME="Index1649"></A><A NAME="Index1650"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Choice</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
box is not like the combo box in Windows, which lets you select from a list 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>or</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
type in your own selection. With a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Choice</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
box you choose one and only one element from the list. In the following
example, the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Choice</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
box starts with a certain number of entries and then new entries are added to
the box when a button is pressed. This allows you to see some interesting
behaviors in 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Choice</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
boxes:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: Choice1.java</font>
<font color="#009900">// Using drop-down lists</font>
<font color="#0000ff">import</font> java.awt.*;
<font color="#0000ff">import</font> java.applet.*;

<font color="#0000ff">public</font> <font color="#0000ff">class</font> Choice1 <font color="#0000ff">extends</font> Applet {
  String[] description = { "Ebullient", "Obtuse",
    "Recalcitrant", "Brilliant", "Somnescent",
    "Timorous", "Florid", "Putrescent" };
  TextField t = <font color="#0000ff">new</font> TextField(30);
  Choice c = <font color="#0000ff">new</font> Choice();
  Button b = <font color="#0000ff">new</font> Button("Add items");
  <font color="#0000ff">int</font> count = 0;
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> init() {
    t.setEditable(<font color="#0000ff">false</font>);
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; 4; i++)
      c.addItem(description[count++]);
    add(t);
    add(c);
    add(b);
  }
  <font color="#0000ff">public</font> <font color="#0000ff">boolean</font> action (Event evt, Object arg) {
    <font color="#0000ff">if</font>(evt.target.equals(c))
      t.setText("index: " +  c.getSelectedIndex()
        + "   " + (String)arg);
    <font color="#0000ff">else</font> <font color="#0000ff">if</font>(evt.target.equals(b)) {
      <font color="#0000ff">if</font>(count &lt; description.length)
        c.addItem(description[count++]);
    } 
    <font color="#0000ff">else</font> 
      <font color="#0000ff">return</font> <font color="#0000ff">super</font>.action(evt, arg);
    <font color="#0000ff">return</font> <font color="#0000ff">true</font>;
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>TextField</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
displays the &#8220;selected index,&#8221; which is the sequence number of the
currently selected element, as well as the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
representation of the second argument of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>action(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
which is in this case the string that was selected.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">When
you run this applet, pay attention to the determination of the size of the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Choice</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
box: in Windows, the size is fixed from the first time you drop down the list.
This means that if you drop down the list, then add more elements to the list,
the elements will be there but the drop-down list won&#8217;t get any longer
</FONT><A NAME="fnB57" HREF="#fn57">[57]</A><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
(you can scroll through the elements). However, if you add all the elements
before the first time the list is dropped down, then it will be sized
correctly. Of course, the user will expect to see the whole list when
it&#8217;s dropped down, so this behavior puts some significant limitations on
adding elements to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Choice</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
boxes.
</FONT><a name="_Toc375545455"></a><a name="_Toc408018691"></a><P></DIV>
<HR><DIV ALIGN=LEFT><A NAME="fn57" HREF="#fnB57">[57]</A><FONT FACE="Carmina Md BT" SIZE=2 COLOR="Black">
This behavior is apparently a bug and will be fixed in a later version of Java.
</FONT><P></DIV>


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