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<title>The Java Language Specification The Package java.lang </title>
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<p><strong>
CHAPTER 20 </strong></p>
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<h1>The Package java.lang </h1>
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The <code>java.lang</code> package contains classes that are fundamental to the design of
the Java language. The most important classes are <code>Object</code>, which is the root of the
class hierarchy, and <code>Class</code>, instances of which represent classes at run time.
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Frequently it is necessary to represent a value of primitive type as if it were an object. The wrapper classes <code>Boolean</code>, <code>Character</code>, <code>Integer</code>, <code>Long</code>, <code>Float</code>, and <code>Double</code> serve this purpose. An object of type <code>Double</code>, for example, contains a field whose type is <code>double</code>, representing that value in such a way that a reference to it can be stored in a variable of reference type. These classes also provide a number of methods for converting among primitive values, as well as supporting such standard methods as <code>equals</code> and <code>hashCode</code>.<p>
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The class <code>Math</code> provides commonly used mathematical functions such as sine, cosine, and square root. The classes <code>String</code> and <code>StringBuffer</code> similarly provide commonly used operations on character strings.<p>
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Classes <code>ClassLoader</code>, <code>Process</code>, <code>Runtime</code>, <code>SecurityManager</code>, and <code>System</code> provide "system operations" that manage the dynamic loading of classes, creation of external processes, host environment inquiries such as the time of day, and enforcement of security policies.<p>
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Class <code>Throwable</code> encompasses objects that may be thrown by the <code>throw</code> statement <a href="14.doc.html#237350">(§14.16)</a>. Subclasses of <code>Throwable</code> represent errors and exceptions.<p>
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The hierarchy of classes defined in package <code>java.lang</code> is as follows.<p>
<pre><a name="20232"></a><code><b>Object</b></code> <code><b><a href="javalang.doc1.html#46442">§20.1</a></b></code>
<a name="31472"></a><code><b> </b></code>interface <code><b>Cloneable</b></code> <code><b><a href="javalang.doc1.html#31348">§20.2</a>
</b></code><a name="31477"></a><code><b> Class</b></code> <code><b><a href="javalang.doc2.html#14342">§20.3</a>
</b></code><a name="20278"></a><code><b> Boolean</b></code> <code><b><a href="javalang.doc3.html#14344">§20.4</a>
</b></code><a name="20279"></a><code><b> Character</b></code> <code><b><a href="javalang.doc4.html#14345">§20.5</a>
</b></code><a name="20280"></a><code><b> Number</b></code> <code><b><a href="javalang.doc5.html#2349">§20.6</a>
</b></code><a name="20281"></a><code><b> Integer</b></code> <code><b><a href="javalang.doc6.html#14348">§20.7</a>
</b></code><a name="20282"></a><code><b> Long</b></code> <code><b><a href="javalang.doc7.html#46750">§20.8</a>
</b></code><a name="20283"></a><code><b> Float</b></code> <code><b><a href="javalang.doc8.html#14394">§20.9</a>
</b></code><a name="20284"></a><code><b> Double</b></code> <code><b><a href="javalang.doc9.html#14390">§20.10</a>
</b></code><a name="20285"></a><code><b> Math</b></code> <code><b><a href="javalang.doc10.html#47547">§20.11</a>
</b></code><a name="20286"></a><code><b> String</b></code> <code><b><a href="javalang.doc11.html#14460">§20.12</a>
</b></code><a name="20287"></a><code><b> StringBuffer</b></code> <code><b><a href="javalang.doc12.html#14461">§20.13</a>
</b></code><a name="20288"></a><code><b> ClassLoader</b></code> <code><b><a href="javalang.doc13.html#14462">§20.14</a>
</b></code><a name="20289"></a><code><b> Process</b></code> <code><b><a href="javalang.doc14.html#14463">§20.15</a>
</b></code><a name="20290"></a><code><b> Runtime</b></code> <code><b><a href="javalang.doc15.html#2637">§20.16</a>
</b></code><a name="20291"></a><code><b> SecurityManager</b></code> <code><b><a href="javalang.doc16.html#46274">§20.17</a>
</b></code><a name="31485"></a><code><b> System</b></code> <code><b><a href="javalang.doc17.html#36485">§20.18</a>
</b></code><a name="31490"></a><code><b> </b></code>interface <code><b>Runnable</b></code> <code><b><a href="javalang.doc17.html#2668">§20.19</a>
</b></code><a name="20293"></a><code><b> Thread</b></code> <code><b><a href="javalang.doc18.html#2658">§20.20</a>
</b></code><a name="20294"></a><code><b> ThreadGroup</b></code> <code><b><a href="javalang.doc19.html#14469">§20.21</a>
</b></code><a name="20276"></a><code><b> Throwable</b></code> <code><b><a href="javalang.doc20.html#46198">§20.22</a>
</b></code><a name="20233"></a><code><b> Error
</b></code><a name="20234"></a><code><b> LinkageError
</b></code><a name="20235"></a><code><b> ClassCircularityError
</b></code><a name="20236"></a><code><b> ClassFormatError
</b></code><a name="20237"></a><code><b> ExceptionInInitializerError
</b></code><a name="33346"></a><code><b> IncompatibleClassChangeError
</b></code><a name="20238"></a><code><b> AbstractMethodError
</b></code><a name="20239"></a><code><b> IllegalAccessError
</b></code><a name="20240"></a><code><b> InstantiationError
</b></code><a name="20241"></a><code><b> NoSuchFieldError
</b></code><a name="20242"></a><code><b> NoSuchMethodError
</b></code><a name="20243"></a><code><b> NoClassDefFoundError
</b></code><a name="20244"></a><code><b> UnsatisfiedLinkError
</b></code><a name="20245"></a><code><b> VerifyError
</b></code><a name="20246"></a><code><b> VirtualMachineError
</b></code><a name="20247"></a><code><b> InternalError
</b></code><a name="20248"></a><code><b> OutOfMemoryError
</b></code><a name="20249"></a><code><b> StackOverflowError
</b></code><a name="20250"></a><code><b> UnknownError
</b></code><a name="20251"></a><code><b> ThreadDeath
</b></code><a name="20252"></a><code><b> Exception
</b></code><a name="20253"></a><code><b> ClassNotFoundException
</b></code><a name="31428"></a><code><b> CloneNotSupportedException
</b></code><a name="20254"></a><code><b> IllegalAccessException
</b></code><a name="20255"></a><code><b> InstantiationException
</b></code><a name="20256"></a><code><b> InterruptedException
</b></code><a name="20258"></a><code><b> RuntimeException
</b></code><a name="20259"></a><code><b> ArithmeticException
</b></code><a name="20260"></a><code><b> ArrayStoreException
</b></code><a name="20261"></a><code><b> ClassCastException
</b></code><a name="20262"></a><code><b> IllegalArgumentException
</b></code><a name="20264"></a><code><b> IllegalThreadStateException
</b></code><a name="36571"></a><code><b> NumberFormatException
</b></code><a name="36859"></a><code><b> IllegalMonitorStateException
</b></code><a name="20299"></a><code><b> IndexOutOfBoundsException
</b></code><a name="20302"></a><code><b> NegativeArraySizeException
</b></code><a name="20269"></a><code><b> NullPointerException
</b></code><a name="46441"></a><code><b> SecurityException
</b></code></pre>
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<font size=-1>Java Language Specification (HTML generated by Suzette Pelouch on February 24, 1998)<br>
<i><a href="jcopyright.doc.html">Copyright © 1996 Sun Microsystems, Inc.</a>
All rights reserved</i>
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Please send any comments or corrections to <a href="mailto:doug.kramer@sun.com">doug.kramer@sun.com</a>
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