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<b>Trail:</b> Learning the Java Language
<br /><b>Lesson:</b> Numbers and Strings
<br /><b>Section:</b> Numbers
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<div class="linkLESSON"><a href="index.html">Numbers and Strings</a></div>
<div class="linkAHEAD"><a href="numbers.html">Numbers</a></div>
<div class="nolinkBHEAD">The Numbers Classes</div>
<div class="linkBHEAD"><a href="numberformat.html">Formatting Numeric Print Output</a></div>
<div class="linkBHEAD"><a href="beyondmath.html">Beyond Basic Arithmetic</a></div>
<div class="linkBHEAD"><a href="numbersummary.html">Summary of Numbers</a></div>
<div class="linkQUESTIONS"><a href="QandE/numbers-questions.html">Questions and Exercises</a></div>
<div class="linkAHEAD"><a href="characters.html">Characters</a></div>
<div class="linkAHEAD"><a href="strings.html">Strings</a></div>
<div class="linkBHEAD"><a href="converting.html">Converting Between Numbers and Strings</a></div>
<div class="linkBHEAD"><a href="manipstrings.html">Manipulating Characters in a String</a></div>
<div class="linkBHEAD"><a href="comparestrings.html">Comparing Strings and Portions of Strings</a></div>
<div class="linkBHEAD"><a href="buffers.html">The StringBuilder Class</a></div>
<div class="linkBHEAD"><a href="stringsummary.html">Summary of Characters and Strings</a></div>
<div class="linkAHEAD"><a href="autoboxing.html">Autoboxing and Unboxing</a></div>
<div class="linkQUESTIONS"><a href="QandE/characters-questions.html">Questions and Exercises</a></div>
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<div id="PageTitle"><h1>The Numbers Classes</h1></div>
<div id="PageContent">
<p>When working with numbers, most of the time you use the primitive types in your code. For example:</p>
<div class="codeblock"><pre>
int i = 500;
float gpa = 3.65f;
byte mask = 0xff;
</pre></div>
<p>There are, however, reasons to use objects in place of primitives, and the Java platform provides <i>wrapper</i> classes for each of the primitive data types. These classes "wrap" the primitive in an object. Often, the wrapping is done by the compiler—if you use a primitive where an object is expected, the compiler <i>boxes</i> the primitive in its wrapper class for you. Similarly, if you use a number object when a primitive is expected, the compiler <i>unboxes</i> the object for you. For more information, see
<a class="TutorialLink" target="_top" href="autoboxing.html">Autoboxing and Unboxing</a></p>
<p>All of the numeric wrapper classes are subclasses of the abstract class <code>Number</code>: <!-- figure --></p>
<center><img src="../../figures/java/objects-numberHierarchy.gif" width="327" height="149" align="bottom" alt="The class hierarchy of Number." /></center><div class="note"><hr /><strong>Note:</strong> There are four other subclasses of <code>Number</code> that are not discussed here. <code>BigDecimal</code> and <code>BigInteger</code> are used for high-precision calculations. <code>AtomicInteger</code> and <code>AtomicLong</code> are used for multi-threaded applications.
<hr /></div>
<p>There are three reasons that you might use a <code>Number</code> object rather than a primitive:</p>
<ol>
<li>As an argument of a method that expects an object (often used when manipulating collections of numbers).</li>
<li>To use constants defined by the class, such as <code>MIN_VALUE</code> and <code>MAX_VALUE</code>, that provide the upper and lower bounds of the data type.</li>
<li>To use class methods for converting values to and from other primitive types, for converting to and from strings, and for converting between number systems (decimal, octal, hexadecimal, binary).</li>
</ol>
<p>The following table lists the instance methods that all the subclasses of the <code>Number</code> class implement.</p>
<table border="1" cellpadding="4" cellspacing="3" summary="This table lists methods implemented by all subclasses of Number">
<caption style="font-weight: bold">Methods Implemented by all Subclasses of Number</caption>
<tr>
<th id="h1">Method</th>
<th id="h2">Description</th>
</tr>
<tr>
<td headers="h1"><code>byte byteValue()<br />
short shortValue()<br />
int intValue()<br />
long longValue()<br />
float floatValue()<br />
double doubleValue()</code></td>
<td headers="h2">Converts the value of this <code>Number</code> object to the primitive data type returned.</td>
</tr>
<tr>
<td headers="h1"><code>int compareTo(Byte anotherByte)<br />
int compareTo(Double anotherDouble)<br />
int compareTo(Float anotherFloat)<br />
int compareTo(Integer anotherInteger)<br />
int compareTo(Long anotherLong)<br />
int compareTo(Short anotherShort)</code></td>
<td headers="h2">Compares this <code>Number</code> object to the argument.</td>
</tr>
<tr>
<td headers="h1"><code>boolean equals(Object obj)</code></td>
<td headers="h2">Determines whether this number object is equal to the argument.<br />
The methods return <code>true</code> if the argument is not <code>null</code> and is an object of the same type and with the same numeric value.<br />
There are some extra requirements for <code>Double</code> and <code>Float</code> objects that are described in the Java API documentation.</td>
</tr>
</table>
<p>Each <code>Number</code> class contains other methods that are useful for converting numbers to and from strings and for converting between number systems. The following table lists these methods in the <code>Integer</code> class. Methods for the other <code>Number</code> subclasses are similar:</p>
<table border="1" cellpadding="4" cellspacing="3" summary="This table lists conversion methods for the Integer class">
<caption style="font-weight: bold">Conversion Methods, <code>Integer</code> Class</caption>
<tr>
<th id="h101">Method</th>
<th id="h102">Description</th>
</tr>
<tr>
<td headers="h101"><code>static Integer decode(String s)</code></td>
<td headers="h102">Decodes a string into an integer. Can accept string representations of decimal, octal, or hexadecimal numbers as input.</td>
</tr>
<tr>
<td headers="h101"><code>static int parseInt(String s)</code></td>
<td headers="h102">Returns an integer (decimal only).</td>
</tr>
<tr>
<td headers="h101"><code>static int parseInt(String s, int radix)</code></td>
<td headers="h102">Returns an integer, given a string representation of decimal, binary, octal, or hexadecimal (<code>radix</code> equals 10, 2, 8, or 16 respectively) numbers as input.</td>
</tr>
<tr>
<td headers="h101"><code>String toString()</code></td>
<td headers="h102">Returns a <code>String</code> object representing the value of this <code>Integer</code>.</td>
</tr>
<tr>
<td headers="h101"><code>static String toString(int i)</code></td>
<td headers="h102">Returns a <code>String</code> object representing the specified integer.</td>
</tr>
<tr>
<td headers="h101"><code>static Integer valueOf(int i)</code></td>
<td headers="h102">Returns an <code>Integer</code> object holding the value of the specified primitive.</td>
</tr>
<tr>
<td headers="h101"><code>static Integer valueOf(String s)</code></td>
<td headers="h102">Returns an <code>Integer</code> object holding the value of the specified string representation.</td>
</tr>
<tr>
<td headers="h101"><code>static Integer valueOf(String s, int radix)</code></td>
<td headers="h102">Returns an <code>Integer</code> object holding the integer value of the specified string representation, parsed with the value of radix. For example, if s = "333" and radix = 8, the method returns the base-ten integer equivalent of the octal number 333.</td>
</tr>
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