epubjs

<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head><title>Tables</title><link rel="stylesheet" href="core.css" type="text/css"/><meta name="generator" content="DocBook XSL Stylesheets V1.74.0"/></head><body><div class="sect1" title="Tables"><div class="titlepage"><div><div><h1 class="title"><a id="learnjava3-CHP-18-SECT-3"/>Tables</h1></div></div></div><p><a id="idx11026" class="indexterm"/> Tables present information in orderly rows and columns. This is useful for presenting financial figures or representing data from a relational database. Like trees, tables in Swing are incredibly powerful and customizable. If you go with the default options, they’re also pretty easy to use.</p><p>The <a id="I_indexterm18_id802173" class="indexterm"/><code class="literal">JTable</code> class represents a visual table component. A <code class="literal">JTable</code> is based on a <code class="literal">TableModel</code>, one of a dozen or so supporting interfaces and classes in the <a id="I_indexterm18_id802195" class="indexterm"/><code class="literal">javax.swing.table</code> package.</p><div class="sect2" title="A First Stab: Freeloading"><div class="titlepage"><div><div><h2 class="title"><a id="learnjava3-CHP-18-SECT-3.1"/>A First Stab: Freeloading</h2></div></div></div><p><a id="idx11029" class="indexterm"/> <code class="literal">JTable</code> has one constructor that creates a default table model for you from arrays of data. You just need to supply it with the names of your column headers and a 2D array of <code class="literal">Object</code>s representing the table’s data. The first index selects the table’s row; the second index selects the column. The following example shows how easy it is to get going with tables using this constructor:</p><a id="I_18_tt1084"/><pre class="programlisting"> <code class="c1">//file: DullShipTable.java</code> <code class="kn">import</code> <code class="nn">java.awt.*</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">java.awt.event.*</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">javax.swing.*</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">javax.swing.table.*</code><code class="o">;</code> <code class="kd">public</code> <code class="kd">class</code> <code class="nc">DullShipTable</code> <code class="o">{</code> <code class="kd">public</code> <code class="kd">static</code> <code class="kt">void</code> <code class="nf">main</code><code class="o">(</code><code class="n">String</code><code class="o">[]</code> <code class="n">args</code><code class="o">)</code> <code class="o">{</code> <code class="c1">// create some tabular data</code> <code class="n">String</code><code class="o">[]</code> <code class="n">headings</code> <code class="o">=</code> <code class="k">new</code> <code class="n">String</code><code class="o">[]</code> <code class="o">{</code><code class="s">"Number"</code><code class="o">,</code> <code class="s">"Hot?"</code><code class="o">,</code> <code class="s">"Origin"</code><code class="o">,</code> <code class="s">"Destination"</code><code class="o">,</code> <code class="s">"Ship Date"</code><code class="o">,</code> <code class="s">"Weight"</code> <code class="o">};</code> <code class="n">Object</code><code class="o">[][]</code> <code class="n">data</code> <code class="o">=</code> <code class="k">new</code> <code class="n">Object</code><code class="o">[][]</code> <code class="o">{</code> <code class="o">{</code> <code class="s">"100420"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">FALSE</code><code class="o">,</code> <code class="s">"Des Moines IA"</code><code class="o">,</code> <code class="s">"Spokane WA"</code><code class="o">,</code> <code class="s">"02/06/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">450</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"202174"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">TRUE</code><code class="o">,</code> <code class="s">"Basking Ridge NJ"</code><code class="o">,</code> <code class="s">"Princeton NJ"</code><code class="o">,</code> <code class="s">"05/20/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">1250</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"450877"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">TRUE</code><code class="o">,</code> <code class="s">"St. Paul MN"</code><code class="o">,</code> <code class="s">"Austin TX"</code><code class="o">,</code> <code class="s">"03/20/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">1745</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"101891"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">FALSE</code><code class="o">,</code> <code class="s">"Boston MA"</code><code class="o">,</code> <code class="s">"Albany NY"</code><code class="o">,</code> <code class="s">"04/04/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">88</code><code class="o">)</code> <code class="o">}</code> <code class="o">};</code> <code class="c1">// create the data model and the JTable</code> <code class="n">JTable</code> <code class="n">table</code> <code class="o">=</code> <code class="k">new</code> <code class="n">JTable</code><code class="o">(</code><code class="n">data</code><code class="o">,</code> <code class="n">headings</code><code class="o">);</code> <code class="n">JFrame</code> <code class="n">frame</code> <code class="o">=</code> <code class="k">new</code> <code class="n">JFrame</code><code class="o">(</code><code class="s">"DullShipTable v1.0"</code><code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">add</code><code class="o">(</code><code class="k">new</code> <code class="n">JScrollPane</code><code class="o">(</code><code class="n">table</code><code class="o">));</code> <code class="n">frame</code><code class="o">.</code><code class="na">setDefaultCloseOperation</code><code class="o">(</code> <code class="n">JFrame</code><code class="o">.</code><code class="na">EXIT_ON_CLOSE</code> <code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">setSize</code><code class="o">(</code><code class="mi">500</code><code class="o">,</code> <code class="mi">200</code><code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">setVisible</code><code class="o">(</code><code class="kc">true</code><code class="o">);</code> <code class="o">}</code> <code class="o">}</code></pre><p>This small application produces the display shown in <a class="xref" href="ch18s03.html#learnjava3-CHP-18-FIG-7" title="Figure 18-7. A rudimentary JTable">Figure 18-7</a>.</p><div class="figure"><a id="learnjava3-CHP-18-FIG-7"/><div class="figure-contents"><div class="mediaobject"><a id="I_18_tt1085"/><img src="httpatomoreillycomsourceoreillyimages1707673.png" alt="A rudimentary JTable"/></div></div><p class="title">Figure 18-7. A rudimentary JTable</p></div><p>For very little typing, we’ve gotten some pretty impressive stuff. Here are a few things that come for free:</p><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Column headings</em></span></span></dt><dd><p>The <code class="literal">JTable</code> has automatically formatted the column headings differently than the table cells. It’s clear that they are not part of the table’s data area.</p></dd><dt><span class="term"><span class="emphasis"><em>Cell overflow</em></span></span></dt><dd><p>If a cell’s data is too long to fit in the cell, it is automatically truncated and shown with an ellipsis (...). This is shown in the Origin cell in the second row in <a class="xref" href="ch18s03.html#learnjava3-CHP-18-FIG-7" title="Figure 18-7. A rudimentary JTable">Figure 18-7</a>.</p></dd><dt><span class="term"><span class="emphasis"><em>Row selection</em></span></span></dt><dd><p>You can click on any cell in the table to select its entire row. This behavior is controllable; you can select single cells, entire rows, entire columns, or some combination of these. To configure the <code class="literal">JTable</code>’s selection behavior, use the <a id="I_indexterm18_id802339" class="indexterm"/><code class="literal">setCellSelectionEnabled()</code>, <a id="I_indexterm18_id802350" class="indexterm"/><code class="literal">setColumnSelectionAllowed()</code>, and <a id="I_indexterm18_id802361" class="indexterm"/><code class="literal">setRowSelectionAllowed()</code> methods.</p></dd><dt><span class="term"><span class="emphasis"><em>Cell editing</em></span></span></dt><dd><p>Double-clicking on a cell opens it for editing; you’ll get a little cursor in the cell. You can type directly into the cell to change the cell’s data.</p></dd><dt><span class="term"><span class="emphasis"><em>Column sizing</em></span></span></dt><dd><p>If you position the mouse cursor between two column headings, you’ll get a little left-right arrow cursor. Click and drag to change the size of the column to the left. Depending on how the <code class="literal">JTable</code> is configured, the other columns may also change size. The resizing behavior is controlled with the <a id="I_indexterm18_id802401" class="indexterm"/><code class="literal">setAutoResizeMode()</code> method.</p></dd><dt><span class="term"><span class="emphasis"><em>Column reordering</em></span></span></dt><dd><p>If you click and drag on a column heading, you can move the entire column to another part of the table.</p></dd></dl></div><p>Play with this for a while. It’s fun!<a id="I_indexterm18_id802424" class="indexterm"/></p></div><div class="sect2" title="Round Two: Creating a Table Model"><div class="titlepage"><div><div><h2 class="title"><a id="learnjava3-CHP-18-SECT-3.2"/>Round Two: Creating a Table Model</h2></div></div></div><p><a id="idx11028" class="indexterm"/> <code class="literal">JTable</code> is a very powerful component. You get a lot of very nice behavior for free. However, the default settings are not quite what we wanted for this simple example. In particular, we intended the table entries to be read-only; they should not be editable. Also, we’d like entries in the Hot? column to be checkboxes instead of words. Finally, it would be nice if the Weight column were formatted appropriately for numbers rather than for text.</p><p>To achieve more flexibility with <a id="I_indexterm18_id802466" class="indexterm"/><code class="literal">JTable</code>, we’ll write our own data model by implementing the <a id="I_indexterm18_id802478" class="indexterm"/><code class="literal">TableModel</code> interface. Fortunately, Swing makes this easy by supplying a class that does most of the work, <a id="I_indexterm18_id802490" class="indexterm"/><code class="literal">AbstractTableModel</code>. To create a table model, we’ll just subclass <code class="literal">AbstractTableModel</code> and override whatever behavior we want to change.</p><p>At a minimum, all <code class="literal">AbstractTableModel</code> subclasses have to define the following three methods:</p><div class="variablelist"><dl><dt><span class="term"><code class="literal">public int getRowCount()</code>, <code class="literal">public int getColumnCount()</code></span></dt><dd><p>Returns the number of rows and columns in this data model</p></dd><dt><span class="term"><code class="literal">public Object getValueAt(int</code> <em class="replaceable"><code>row</code></em> <code class="literal">, int</code> <em class="replaceable"><code>column</code></em> <code class="literal">)</code></span></dt><dd><p>Returns the value for the given cell</p></dd></dl></div><p>When the <code class="literal">JTable</code> needs data values, it calls the <a id="I_indexterm18_id802568" class="indexterm"/><code class="literal">getValueAt()</code> method in the table model. To get an idea of the total size of the table, <code class="literal">JTable</code> calls the <a id="I_indexterm18_id802585" class="indexterm"/><code class="literal">getRowCount()</code> and <a id="I_indexterm18_id802596" class="indexterm"/><code class="literal">getColumnCount()</code> methods in the table model.</p><p>A very simple table model looks like this:</p><a id="I_18_tt1086"/><pre class="programlisting"> <code class="kd">public</code> <code class="kd">static</code> <code class="kd">class</code> <code class="nc">ShipTableModel</code> <code class="kd">extends</code> <code class="n">AbstractTableModel</code> <code class="o">{</code> <code class="kd">private</code> <code class="n">Object</code><code class="o">[][]</code> <code class="n">data</code> <code class="o">=</code> <code class="k">new</code> <code class="n">Object</code><code class="o">[][]</code> <code class="o">{</code> <code class="o">{</code> <code class="s">"100420"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">FALSE</code><code class="o">,</code> <code class="s">"Des Moines IA"</code><code class="o">,</code> <code class="s">"Spokane WA"</code><code class="o">,</code> <code class="s">"02/06/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">450</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"202174"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">TRUE</code><code class="o">,</code> <code class="s">"Basking Ridge NJ"</code><code class="o">,</code> <code class="s">"Princeton NJ"</code><code class="o">,</code> <code class="s">"05/20/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">1250</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"450877"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">TRUE</code><code class="o">,</code> <code class="s">"St. Paul MN"</code><code class="o">,</code> <code class="s">"Austin TX"</code><code class="o">,</code> <code class="s">"03/20/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">1745</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"101891"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">FALSE</code><code class="o">,</code> <code class="s">"Boston MA"</code><code class="o">,</code> <code class="s">"Albany NY"</code><code class="o">,</code> <code class="s">"04/04/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">88</code><code class="o">)</code> <code class="o">}</code> <code class="o">};</code> <code class="kd">public</code> <code class="kt">int</code> <code class="nf">getRowCount</code><code class="o">()</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">.</code><code class="na">length</code><code class="o">;</code> <code class="o">}</code> <code class="kd">public</code> <code class="kt">int</code> <code class="nf">getColumnCount</code><code class="o">()</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="mi">0</code><code class="o">].</code><code class="na">length</code><code class="o">;</code> <code class="o">}</code> <code class="kd">public</code> <code class="n">Object</code> <code class="nf">getValueAt</code><code class="o">(</code><code class="kt">int</code> <code class="n">row</code><code class="o">,</code> <code class="kt">int</code> <code class="n">column</code><code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="n">row</code><code class="o">][</code><code class="n">column</code><code class="o">];</code> <code class="o">}</code> <code class="o">}</code></pre><p>We’d like to use the same column headings that we used in the previous example. The table model supplies these through a method called <a id="I_indexterm18_id802629" class="indexterm"/><code class="literal">getColumnName()</code>. We could add column headings to our simple table model like this:</p><a id="I_18_tt1087"/><pre class="programlisting"> <code class="kd">private</code> <code class="n">String</code><code class="o">[]</code> <code class="n">headings</code> <code class="o">=</code> <code class="k">new</code> <code class="n">String</code><code class="o">[]</code> <code class="o">{</code> <code class="s">"Number"</code><code class="o">,</code> <code class="s">"Hot?"</code><code class="o">,</code> <code class="s">"Origin"</code><code class="o">,</code> <code class="s">"Destination"</code><code class="o">,</code> <code class="s">"Ship Date"</code><code class="o">,</code> <code class="s">"Weight"</code> <code class="o">};</code> <code class="kd">public</code> <code class="n">String</code> <code class="nf">getColumnName</code><code class="o">(</code><code class="kt">int</code> <code class="n">column</code><code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="n">headings</code><code class="o">[</code><code class="n">column</code><code class="o">];</code> <code class="o">}</code></pre><p>By default, <code class="literal">AbstractTableModel</code> makes all its cells noneditable, which is what we wanted. No changes need to be made for this.</p><p>The final modification is to have the Hot? column and the Weight column formatted specially. To do this, we give our table model some knowledge about the column types. <code class="literal">JTable</code> automatically generates checkbox cells for <code class="literal">Boolean</code> column types and specially formatted number cells for <code class="literal">Number</code> types. To give the table model some intelligence about its column types, we override the <a id="I_indexterm18_id802681" class="indexterm"/><code class="literal">getColumnClass()</code> method. The <code class="literal">JTable</code> calls this method to determine the data type of each column. It may then represent the data in a special way. This table model returns the class of the item in the first row of its data:</p><a id="I_18_tt1088"/><pre class="programlisting"> <code class="kd">public</code> <code class="n">Class</code> <code class="nf">getColumnClass</code><code class="o">(</code><code class="kt">int</code> <code class="n">column</code><code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="mi">0</code><code class="o">][</code><code class="n">column</code><code class="o">].</code><code class="na">getClass</code><code class="o">();</code> <code class="o">}</code></pre><p>That’s really all there is to do. The following complete example illustrates how you can use your own table model to create a <code class="literal">JTable</code> using the techniques just described:</p><a id="I_18_tt1089"/><pre class="programlisting"> <code class="c1">//file: ShipTable.java</code> <code class="kn">import</code> <code class="nn">java.awt.*</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">java.awt.event.*</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">javax.swing.*</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">javax.swing.table.*</code><code class="o">;</code> <code class="kd">public</code> <code class="kd">class</code> <code class="nc">ShipTable</code> <code class="o">{</code> <code class="kd">public</code> <code class="kd">static</code> <code class="kd">class</code> <code class="nc">ShipTableModel</code> <code class="kd">extends</code> <code class="n">AbstractTableModel</code> <code class="o">{</code> <code class="kd">private</code> <code class="n">String</code><code class="o">[]</code> <code class="n">headings</code> <code class="o">=</code> <code class="k">new</code> <code class="n">String</code><code class="o">[]</code> <code class="o">{</code> <code class="s">"Number"</code><code class="o">,</code> <code class="s">"Hot?"</code><code class="o">,</code> <code class="s">"Origin"</code><code class="o">,</code> <code class="s">"Destination"</code><code class="o">,</code> <code class="s">"Ship Date"</code><code class="o">,</code> <code class="s">"Weight"</code> <code class="o">};</code> <code class="kd">private</code> <code class="n">Object</code><code class="o">[][]</code> <code class="n">data</code> <code class="o">=</code> <code class="k">new</code> <code class="n">Object</code><code class="o">[][]</code> <code class="o">{</code> <code class="o">{</code> <code class="s">"100420"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">FALSE</code><code class="o">,</code> <code class="s">"Des Moines IA"</code><code class="o">,</code> <code class="s">"Spokane WA"</code><code class="o">,</code> <code class="s">"02/06/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">450</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"202174"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">TRUE</code><code class="o">,</code> <code class="s">"Basking Ridge NJ"</code><code class="o">,</code> <code class="s">"Princeton NJ"</code><code class="o">,</code> <code class="s">"05/20/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">1250</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"450877"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">TRUE</code><code class="o">,</code> <code class="s">"St. Paul MN"</code><code class="o">,</code> <code class="s">"Austin TX"</code><code class="o">,</code> <code class="s">"03/20/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">1745</code><code class="o">)</code> <code class="o">},</code> <code class="o">{</code> <code class="s">"101891"</code><code class="o">,</code> <code class="n">Boolean</code><code class="o">.</code><code class="na">FALSE</code><code class="o">,</code> <code class="s">"Boston MA"</code><code class="o">,</code> <code class="s">"Albany NY"</code><code class="o">,</code> <code class="s">"04/04/2000"</code><code class="o">,</code> <code class="k">new</code> <code class="n">Float</code><code class="o">(</code><code class="mi">88</code><code class="o">)</code> <code class="o">}</code> <code class="o">};</code> <code class="kd">public</code> <code class="kt">int</code> <code class="nf">getRowCount</code><code class="o">()</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">.</code><code class="na">length</code><code class="o">;</code> <code class="o">}</code> <code class="kd">public</code> <code class="kt">int</code> <code class="nf">getColumnCount</code><code class="o">()</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="mi">0</code><code class="o">].</code><code class="na">length</code><code class="o">;</code> <code class="o">}</code> <code class="kd">public</code> <code class="n">Object</code> <code class="nf">getValueAt</code><code class="o">(</code><code class="kt">int</code> <code class="n">row</code><code class="o">,</code> <code class="kt">int</code> <code class="n">column</code><code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="n">row</code><code class="o">][</code><code class="n">column</code><code class="o">];</code> <code class="o">}</code> <code class="kd">public</code> <code class="n">String</code> <code class="nf">getColumnName</code><code class="o">(</code><code class="kt">int</code> <code class="n">column</code><code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="n">headings</code><code class="o">[</code><code class="n">column</code><code class="o">];</code> <code class="o">}</code> <code class="kd">public</code> <code class="n">Class</code> <code class="nf">getColumnClass</code><code class="o">(</code><code class="kt">int</code> <code class="n">column</code><code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="mi">0</code><code class="o">][</code><code class="n">column</code><code class="o">].</code><code class="na">getClass</code><code class="o">();</code> <code class="o">}</code> <code class="o">}</code> <code class="kd">public</code> <code class="kd">static</code> <code class="kt">void</code> <code class="nf">main</code><code class="o">(</code><code class="n">String</code><code class="o">[]</code> <code class="n">args</code><code class="o">)</code> <code class="o">{</code> <code class="c1">// create the data model and the JTable</code> <code class="n">TableModel</code> <code class="n">model</code> <code class="o">=</code> <code class="k">new</code> <code class="n">ShipTableModel</code><code class="o">();</code> <code class="n">JTable</code> <code class="n">table</code> <code class="o">=</code> <code class="k">new</code> <code class="n">JTable</code><code class="o">(</code><code class="n">model</code><code class="o">);</code> <code class="n">table</code><code class="o">.</code><code class="na">setAutoResizeMode</code><code class="o">(</code><code class="n">JTable</code><code class="o">.</code><code class="na">AUTO_RESIZE_OFF</code><code class="o">);</code> <code class="n">JFrame</code> <code class="n">frame</code> <code class="o">=</code> <code class="k">new</code> <code class="n">JFrame</code><code class="o">(</code><code class="s">"ShipTable v1.0"</code><code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">getContentPane</code><code class="o">().</code><code class="na">add</code><code class="o">(</code><code class="k">new</code> <code class="n">JScrollPane</code><code class="o">(</code><code class="n">table</code><code class="o">));</code> <code class="n">frame</code><code class="o">.</code><code class="na">setDefaultCloseOperation</code><code class="o">(</code> <code class="n">JFrame</code><code class="o">.</code><code class="na">EXIT_ON_CLOSE</code> <code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">setSize</code><code class="o">(</code><code class="mi">500</code><code class="o">,</code> <code class="mi">200</code><code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">setVisible</code><code class="o">(</code><code class="kc">true</code><code class="o">);</code> <code class="o">}</code> <code class="o">}</code></pre><p>The running application is shown in <a class="xref" href="ch18s03.html#learnjava3-CHP-18-FIG-8" title="Figure 18-8. Customizing a table">Figure 18-8</a>.<a id="I_indexterm18_id802749" class="indexterm"/></p><div class="figure"><a id="learnjava3-CHP-18-FIG-8"/><div class="figure-contents"><div class="mediaobject"><a id="I_18_tt1090"/><img src="httpatomoreillycomsourceoreillyimages1707674.png" alt="Customizing a table"/></div></div><p class="title">Figure 18-8. Customizing a table</p></div></div><div class="sect2" title="Round Three: A Simple Spreadsheet"><div class="titlepage"><div><div><h2 class="title"><a id="learnjava3-CHP-18-SECT-3.3"/>Round Three: A Simple Spreadsheet</h2></div></div></div><p><a id="idx11021" class="indexterm"/> <a id="idx11030" class="indexterm"/>To illustrate just how powerful and flexible the separation of the data model from the GUI can be, we’ll show a more complex model. In the following example, we’ll implement a very slim but functional spreadsheet (see <a class="xref" href="ch18s03.html#learnjava3-CHP-18-FIG-9" title="Figure 18-9. A simple spreadsheet">Figure 18-9</a>) using almost no customization of the <code class="literal">JTable</code>. All of the data processing is in a <code class="literal">TableModel</code> called <code class="literal">SpreadSheetModel</code>.</p><div class="figure"><a id="learnjava3-CHP-18-FIG-9"/><div class="figure-contents"><div class="mediaobject"><a id="I_18_tt1091"/><img src="httpatomoreillycomsourceoreillyimages1707675.png" alt="A simple spreadsheet"/></div></div><p class="title">Figure 18-9. A simple spreadsheet</p></div><p>Our spreadsheet does the expected stuff—allowing you to enter numbers or mathematical expressions such as <code class="literal">(A1*B2)+C3</code> into each cell.<sup>[<a id="learnjava3-CHP-18-FN-1" href="#ftn.learnjava3-CHP-18-FN-1" class="footnote">41</a>]</sup> All cell editing and updating is driven by the standard <a id="I_indexterm18_id802867" class="indexterm"/><code class="literal">JTable</code>. We implement the methods necessary to set and retrieve cell data. Of course, we don’t do any real validation here, so it’s easy to break our table. (For example, there is no check for circular dependencies, which may be undesirable.)</p><p>As you will see, the bulk of the code in this example is in the inner class used to parse the value of the equations in the cells. If you don’t find this part interesting, you might want to skip ahead. But if you have never seen an example of this kind of parsing before, we think you will find it to be very cool. Through the magic of recursion and Java’s powerful <code class="literal">String</code> manipulation, it takes us only about 50 lines of code to implement a parser capable of handling basic arithmetic with arbitrarily nested parentheses.</p><p>Here’s the code:</p><a id="I_18_tt1092"/><pre class="programlisting"> <code class="c1">//file: SpreadsheetModel.java</code> <code class="kn">import</code> <code class="nn">java.util.StringTokenizer</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">javax.swing.*</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">javax.swing.table.AbstractTableModel</code><code class="o">;</code> <code class="kn">import</code> <code class="nn">java.awt.event.*</code><code class="o">;</code> <code class="kd">public</code> <code class="kd">class</code> <code class="nc">SpreadsheetModel</code> <code class="kd">extends</code> <code class="n">AbstractTableModel</code> <code class="o">{</code> <code class="n">Expression</code> <code class="o">[][]</code> <code class="n">data</code><code class="o">;</code> <code class="kd">public</code> <code class="nf">SpreadsheetModel</code><code class="o">(</code> <code class="kt">int</code> <code class="n">rows</code><code class="o">,</code> <code class="kt">int</code> <code class="n">cols</code> <code class="o">)</code> <code class="o">{</code> <code class="n">data</code> <code class="o">=</code> <code class="k">new</code> <code class="n">Expression</code> <code class="o">[</code><code class="n">rows</code><code class="o">][</code><code class="n">cols</code><code class="o">];</code> <code class="o">}</code> <code class="kd">public</code> <code class="kt">void</code> <code class="nf">setValueAt</code><code class="o">(</code><code class="n">Object</code> <code class="n">value</code><code class="o">,</code> <code class="kt">int</code> <code class="n">row</code><code class="o">,</code> <code class="kt">int</code> <code class="n">col</code><code class="o">)</code> <code class="o">{</code> <code class="n">data</code><code class="o">[</code><code class="n">row</code><code class="o">][</code><code class="n">col</code><code class="o">]</code> <code class="o">=</code> <code class="k">new</code> <code class="n">Expression</code><code class="o">(</code> <code class="o">(</code><code class="n">String</code><code class="o">)</code><code class="n">value</code> <code class="o">);</code> <code class="n">fireTableDataChanged</code><code class="o">();</code> <code class="o">}</code> <code class="kd">public</code> <code class="n">Object</code> <code class="nf">getValueAt</code><code class="o">(</code> <code class="kt">int</code> <code class="n">row</code><code class="o">,</code> <code class="kt">int</code> <code class="n">col</code> <code class="o">)</code> <code class="o">{</code> <code class="k">if</code> <code class="o">(</code> <code class="n">data</code><code class="o">[</code><code class="n">row</code><code class="o">][</code><code class="n">col</code><code class="o">]</code> <code class="o">!=</code> <code class="kc">null</code> <code class="o">)</code> <code class="k">try</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="n">row</code><code class="o">][</code><code class="n">col</code><code class="o">].</code><code class="na">eval</code><code class="o">()</code> <code class="o">+</code> <code class="s">""</code><code class="o">;</code> <code class="o">}</code> <code class="k">catch</code> <code class="o">(</code> <code class="n">BadExpression</code> <code class="n">e</code> <code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="s">"Error"</code><code class="o">;</code> <code class="o">}</code> <code class="k">return</code> <code class="s">""</code><code class="o">;</code> <code class="o">}</code> <code class="kd">public</code> <code class="kt">int</code> <code class="nf">getRowCount</code><code class="o">()</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">.</code><code class="na">length</code><code class="o">;</code> <code class="o">}</code> <code class="kd">public</code> <code class="kt">int</code> <code class="nf">getColumnCount</code><code class="o">()</code> <code class="o">{</code> <code class="k">return</code> <code class="n">data</code><code class="o">[</code><code class="mi">0</code><code class="o">].</code><code class="na">length</code><code class="o">;</code> <code class="o">}</code> <code class="kd">public</code> <code class="kt">boolean</code> <code class="nf">isCellEditable</code><code class="o">(</code><code class="kt">int</code> <code class="n">row</code><code class="o">,</code> <code class="kt">int</code> <code class="n">col</code><code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="kc">true</code><code class="o">;</code> <code class="o">}</code> <code class="kd">class</code> <code class="nc">Expression</code> <code class="o">{</code> <code class="n">String</code> <code class="n">text</code><code class="o">;</code> <code class="n">StringTokenizer</code> <code class="n">tokens</code><code class="o">;</code> <code class="n">String</code> <code class="n">token</code><code class="o">;</code> <code class="n">Expression</code><code class="o">(</code> <code class="n">String</code> <code class="n">text</code> <code class="o">)</code> <code class="o">{</code> <code class="k">this</code><code class="o">.</code><code class="na">text</code> <code class="o">=</code> <code class="n">text</code><code class="o">.</code><code class="na">trim</code><code class="o">();</code> <code class="o">}</code> <code class="kt">float</code> <code class="nf">eval</code><code class="o">()</code> <code class="kd">throws</code> <code class="n">BadExpression</code> <code class="o">{</code> <code class="n">tokens</code> <code class="o">=</code> <code class="k">new</code> <code class="n">StringTokenizer</code><code class="o">(</code> <code class="n">text</code><code class="o">,</code> <code class="s">" */+-()"</code><code class="o">,</code> <code class="kc">true</code> <code class="o">);</code> <code class="k">try</code> <code class="o">{</code> <code class="k">return</code> <code class="n">sum</code><code class="o">();</code> <code class="o">}</code> <code class="k">catch</code> <code class="o">(</code> <code class="n">Exception</code> <code class="n">e</code> <code class="o">)</code> <code class="o">{</code> <code class="k">throw</code> <code class="k">new</code> <code class="n">BadExpression</code><code class="o">();</code> <code class="o">}</code> <code class="o">}</code> <code class="kd">private</code> <code class="kt">float</code> <code class="nf">sum</code><code class="o">()</code> <code class="o">{</code> <code class="kt">float</code> <code class="n">value</code> <code class="o">=</code> <code class="n">term</code><code class="o">();</code> <code class="k">while</code><code class="o">(</code> <code class="n">more</code><code class="o">()</code> <code class="o">&&</code> <code class="n">match</code><code class="o">(</code><code class="s">"+-"</code><code class="o">)</code> <code class="o">)</code> <code class="k">if</code> <code class="o">(</code> <code class="n">match</code><code class="o">(</code><code class="s">"+"</code><code class="o">)</code> <code class="o">)</code> <code class="o">{</code> <code class="n">consume</code><code class="o">();</code> <code class="n">value</code> <code class="o">=</code> <code class="n">value</code> <code class="o">+</code> <code class="n">term</code><code class="o">();</code> <code class="o">}</code> <code class="k">else</code> <code class="o">{</code> <code class="n">consume</code><code class="o">();</code> <code class="n">value</code> <code class="o">=</code> <code class="n">value</code> <code class="o">-</code> <code class="n">term</code><code class="o">();</code> <code class="o">}</code> <code class="k">return</code> <code class="n">value</code><code class="o">;</code> <code class="o">}</code> <code class="kd">private</code> <code class="kt">float</code> <code class="nf">term</code><code class="o">()</code> <code class="o">{</code> <code class="kt">float</code> <code class="n">value</code> <code class="o">=</code> <code class="n">element</code><code class="o">();</code> <code class="k">while</code><code class="o">(</code> <code class="n">more</code><code class="o">()</code> <code class="o">&&</code> <code class="n">match</code><code class="o">(</code> <code class="s">"*/"</code><code class="o">)</code> <code class="o">)</code> <code class="k">if</code> <code class="o">(</code> <code class="n">match</code><code class="o">(</code><code class="s">"*"</code><code class="o">)</code> <code class="o">)</code> <code class="o">{</code> <code class="n">consume</code><code class="o">();</code> <code class="n">value</code> <code class="o">=</code> <code class="n">value</code> <code class="o">*</code> <code class="n">element</code><code class="o">();</code> <code class="o">}</code> <code class="k">else</code> <code class="o">{</code> <code class="n">consume</code><code class="o">();</code> <code class="n">value</code> <code class="o">=</code> <code class="n">value</code> <code class="o">/</code> <code class="n">element</code><code class="o">();</code> <code class="o">}</code> <code class="k">return</code> <code class="n">value</code><code class="o">;</code> <code class="o">}</code> <code class="kd">private</code> <code class="kt">float</code> <code class="nf">element</code><code class="o">()</code> <code class="o">{</code> <code class="kt">float</code> <code class="n">value</code><code class="o">;</code> <code class="k">if</code> <code class="o">(</code> <code class="n">match</code><code class="o">(</code> <code class="s">"("</code><code class="o">)</code> <code class="o">)</code> <code class="o">{</code> <code class="n">consume</code><code class="o">();</code> <code class="n">value</code> <code class="o">=</code> <code class="n">sum</code><code class="o">();</code> <code class="o">}</code> <code class="k">else</code> <code class="o">{</code> <code class="n">String</code> <code class="n">svalue</code><code class="o">;</code> <code class="k">if</code> <code class="o">(</code> <code class="n">Character</code><code class="o">.</code><code class="na">isLetter</code><code class="o">(</code> <code class="n">token</code><code class="o">().</code><code class="na">charAt</code><code class="o">(</code><code class="mi">0</code><code class="o">)</code> <code class="o">)</code> <code class="o">)</code> <code class="o">{</code> <code class="kt">int</code> <code class="n">col</code> <code class="o">=</code> <code class="n">findColumn</code><code class="o">(</code> <code class="n">token</code><code class="o">().</code><code class="na">charAt</code><code class="o">(</code><code class="mi">0</code><code class="o">)</code> <code class="o">+</code> <code class="s">""</code> <code class="o">);</code> <code class="kt">int</code> <code class="n">row</code> <code class="o">=</code> <code class="n">Character</code><code class="o">.</code><code class="na">digit</code><code class="o">(</code> <code class="n">token</code><code class="o">().</code><code class="na">charAt</code><code class="o">(</code><code class="mi">1</code><code class="o">),</code> <code class="mi">10</code> <code class="o">);</code> <code class="n">svalue</code> <code class="o">=</code> <code class="o">(</code><code class="n">String</code><code class="o">)</code><code class="n">getValueAt</code><code class="o">(</code> <code class="n">row</code><code class="o">,</code> <code class="n">col</code> <code class="o">);</code> <code class="o">}</code> <code class="k">else</code> <code class="n">svalue</code> <code class="o">=</code> <code class="n">token</code><code class="o">();</code> <code class="n">value</code> <code class="o">=</code> <code class="n">Float</code><code class="o">.</code><code class="na">parseFloat</code><code class="o">(</code> <code class="n">svalue</code> <code class="o">);</code> <code class="o">}</code> <code class="n">consume</code><code class="o">();</code> <code class="c1">// ")" or value token</code> <code class="k">return</code> <code class="n">value</code><code class="o">;</code> <code class="o">}</code> <code class="kd">private</code> <code class="n">String</code> <code class="nf">token</code><code class="o">()</code> <code class="o">{</code> <code class="k">if</code> <code class="o">(</code> <code class="n">token</code> <code class="o">==</code> <code class="kc">null</code> <code class="o">)</code> <code class="k">while</code> <code class="o">(</code> <code class="o">(</code><code class="n">token</code><code class="o">=</code><code class="n">tokens</code><code class="o">.</code><code class="na">nextToken</code><code class="o">()).</code><code class="na">equals</code><code class="o">(</code><code class="s">" "</code><code class="o">)</code> <code class="o">);</code> <code class="k">return</code> <code class="n">token</code><code class="o">;</code> <code class="o">}</code> <code class="kd">private</code> <code class="kt">void</code> <code class="nf">consume</code><code class="o">()</code> <code class="o">{</code> <code class="n">token</code> <code class="o">=</code> <code class="kc">null</code><code class="o">;</code> <code class="o">}</code> <code class="kd">private</code> <code class="kt">boolean</code> <code class="nf">match</code><code class="o">(</code> <code class="n">String</code> <code class="n">s</code> <code class="o">)</code> <code class="o">{</code> <code class="k">return</code> <code class="n">s</code><code class="o">.</code><code class="na">indexOf</code><code class="o">(</code> <code class="n">token</code><code class="o">()</code> <code class="o">)!=-</code><code class="mi">1</code><code class="o">;</code> <code class="o">}</code> <code class="kd">private</code> <code class="kt">boolean</code> <code class="nf">more</code><code class="o">()</code> <code class="o">{</code> <code class="k">return</code> <code class="n">tokens</code><code class="o">.</code><code class="na">hasMoreTokens</code><code class="o">();</code> <code class="o">}</code> <code class="o">}</code> <code class="kd">class</code> <code class="nc">BadExpression</code> <code class="kd">extends</code> <code class="n">Exception</code> <code class="o">{</code> <code class="o">}</code> <code class="kd">public</code> <code class="kd">static</code> <code class="kt">void</code> <code class="nf">main</code><code class="o">(</code> <code class="n">String</code> <code class="o">[]</code> <code class="n">args</code> <code class="o">)</code> <code class="o">{</code> <code class="n">JFrame</code> <code class="n">frame</code> <code class="o">=</code> <code class="k">new</code> <code class="n">JFrame</code><code class="o">(</code><code class="s">"Excelsior!"</code><code class="o">);</code> <code class="n">JTable</code> <code class="n">table</code> <code class="o">=</code> <code class="k">new</code> <code class="n">JTable</code><code class="o">(</code> <code class="k">new</code> <code class="n">SpreadsheetModel</code><code class="o">(</code><code class="mi">15</code><code class="o">,</code> <code class="mi">5</code><code class="o">)</code> <code class="o">);</code> <code class="n">table</code><code class="o">.</code><code class="na">setPreferredScrollableViewportSize</code><code class="o">(</code> <code class="n">table</code><code class="o">.</code><code class="na">getPreferredSize</code><code class="o">()</code> <code class="o">);</code> <code class="n">table</code><code class="o">.</code><code class="na">setCellSelectionEnabled</code><code class="o">(</code><code class="kc">true</code><code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">getContentPane</code><code class="o">().</code><code class="na">add</code><code class="o">(</code> <code class="k">new</code> <code class="n">JScrollPane</code><code class="o">(</code> <code class="n">table</code> <code class="o">)</code> <code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">setDefaultCloseOperation</code><code class="o">(</code> <code class="n">JFrame</code><code class="o">.</code><code class="na">EXIT_ON_CLOSE</code> <code class="o">);</code> <code class="n">frame</code><code class="o">.</code><code class="na">pack</code><code class="o">();</code> <code class="n">frame</code><code class="o">.</code><code class="na">show</code><code class="o">();</code> <code class="o">}</code> <code class="o">}</code></pre><p>Our model extends <a id="I_indexterm18_id802986" class="indexterm"/><code class="literal">AbstractTableModel</code> and overrides just a few methods. As you can see, our data is stored in a 2D array of <code class="literal">Expression</code> objects. The <a id="I_indexterm18_id803003" class="indexterm"/><code class="literal">setValueAt()</code> method of our model creates <code class="literal">Expression</code> objects from the strings typed by the user and stores them in the array. The <a id="I_indexterm18_id803021" class="indexterm"/><code class="literal">getValueAt()</code> method returns a value for a cell by calling the ex