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<br /><b>Lesson:</b> Numbers and Strings

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<div id="PageTitle"><h1>Characters</h1></div>

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<!-- Characters -->

<p>Most of the time, if you are using a single character value, you will use the primitive <code>char</code> type. For example:</p>

<div class="codeblock"><pre>

char ch = 'a';

// Unicode for uppercase Greek omega character

char uniChar = '\u039A';

// an array of chars

char[] charArray = { 'a', 'b', 'c', 'd', 'e' };

</pre></div>

<p>There are times, however, when you need to use a char as an object&#151;for example, as a method argument where an object is expected. The Java programming language provides a <i>wrapper</i> class that &quot;wraps&quot; the <code>char</code> in a <code>Character</code> object for this purpose. An object of type <code>Character</code> contains a single field, whose type is <code>char</code>. This

<a class="SourceLink" target="_blank" href="http://docs.oracle.com/javase/7/docs/api/java/lang/Character.html" onclick="showCode('../../displayCode.html', 'http://docs.oracle.com/javase/7/docs/api/java/lang/Character.html'); return false;"><code>Character</code></a> class also offers a number of useful class (i.e., static) methods for manipulating characters.</p>

<p>You can create a <code>Character</code> object with the <code>Character</code> constructor:</p>

<div class="codeblock"><pre>

Character ch = new Character('a');

</pre></div>

<p>The Java compiler will also create a <code>Character</code> object for you under some circumstances. For example, if you pass a primitive <code>char</code> into a method that expects an object, the compiler automatically converts the <code>char</code> to a <code>Character</code> for you. This feature is called <em>autoboxing</em>&#151;or <em>unboxing</em>, if the conversion goes the other way.</p>

<p>Here is an example of boxing,</p>

<div class="codeblock"><pre>

// the primitive char 'a' is boxed

// into the Character object ch

Character ch = 'a';

</pre></div>

<p>and here is an example of both boxing and unboxing,</p>

<div class="codeblock"><pre>

// method parameter and return

// type = Character object

Character test(Character c) {...}

// primitive 'x' is boxed for method

// test, return is unboxed to char 'c'

char c = test('x');

</pre></div>

<div class="note"><hr /><strong>Note:</strong>&nbsp;The <code>Character</code> class is immutable, so that once it is created, a <code>Character</code> object cannot be changed.

<hr /></div>

<p>The following table lists some of the most useful methods in the <code>Character</code> class, but is not exhaustive. For a complete listing of all methods in this class (there are more than 50), refer to the

<a class="SourceLink" target="_blank" href="http://docs.oracle.com/javase/7/docs/api/java/lang/Character.html" onclick="showCode('../../displayCode.html', 'http://docs.oracle.com/javase/7/docs/api/java/lang/Character.html'); return false;"><code>java.lang.Character</code></a> API specification.</p>

<table width="100%" border="1" cellpadding="4" cellspacing="3" summary="This table lists Character methods">

<caption style="font-weight: bold">Useful Methods in the <code>Character</code> Class</caption>

<tr>

<th id="h1" width="30%">Method</th>

<th id="h2">Description</th>

</tr>

<tr>

<td headers="h1"><code>boolean isLetter(char ch)<br />

boolean isDigit(char ch)</code></td>

<td headers="h2">Determines whether the specified char value is a letter or a digit, respectively.</td>

</tr>

<tr>

<td headers="h1"><code>boolean isWhitespace(char ch)</code></td>

<td headers="h2">Determines whether the specified char value is white space.</td>

</tr>

<tr>

<td headers="h1"><code>boolean isUpperCase(char ch)<br />

boolean isLowerCase(char ch)</code></td>

<td headers="h2">Determines whether the specified char value is uppercase or lowercase, respectively.</td>

</tr>

<tr>

<td headers="h1"><code>char toUpperCase(char ch)<br />

char toLowerCase(char ch)</code></td>

<td headers="h2">Returns the uppercase or lowercase form of the specified char value.</td>

</tr>

<tr>

<td headers="h1"><code>toString(char ch)</code></td>

<td headers="h2">Returns a <code>String</code> object representing the specified character value &#151; that is, a one-character string.</td>

</tr>

</table>

<h2>Escape Sequences</h2>

<p>A character preceded by a backslash (\) is an <i>escape sequence</i> and has special meaning to the compiler. The following table shows the Java escape sequences:</p>

<table width="50%" border="1" cellpadding="4" cellspacing="3" summary="This table lists character sequences used for formatting">

<caption style="font-weight: bold">Escape Sequences</caption>

<tr>

<th id="h101" width="30%">Escape Sequence</th>

<th id="h102">Description</th>

</tr>

<tr>

<td headers="h101"><code>\t</code></td>

<td headers="h102">Insert a tab in the text at this point.</td>

</tr>

<tr>

<td headers="h101"><code>\b</code></td>

<td headers="h102">Insert a backspace in the text at this point.</td>

</tr>

<tr>

<td headers="h101"><code>\n</code></td>

<td headers="h102">Insert a newline in the text at this point.</td>

</tr>

<tr>

<td headers="h101"><code>\r</code></td>

<td headers="h102">Insert a carriage return in the text at this point.</td>

</tr>

<tr>

<td headers="h101"><code>\f</code></td>

<td headers="h102">Insert a formfeed in the text at this point.</td>

</tr>

<tr>

<td headers="h101"><code>\&#39;</code></td>

<td headers="h102">Insert a single quote character in the text at this point.</td>

</tr>

<tr>

<td headers="h101"><code>\&quot;</code></td>

<td headers="h102">Insert a double quote character in the text at this point.</td>

</tr>

<tr>

<td headers="h101"><code>\\</code></td>

<td headers="h102">Insert a backslash character in the text at this point.</td>

</tr>

</table>

<p>When an escape sequence is encountered in a print statement, the compiler interprets it accordingly. For example, if you want to put quotes within quotes you must use the escape sequence, \&quot;, on the interior quotes. To print the sentence</p>

<div class="codeblock"><pre>

She said "Hello!" to me.

</pre></div>

<p>you would write</p>

<div class="codeblock"><pre>

System.out.println("She said \"Hello!\" to me.");

</pre></div>

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