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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN""http://www.w3.org/TR/REC-html40/frameset.dtd"><!--NewPage--><HTML><HEAD><!-- Generated by javadoc on Thu Apr 27 23:36:47 PDT 2000 --><TITLE>Java 2 Platform SE v1.3: Class ArrayList</TITLE><LINK REL ="stylesheet" TYPE="text/css" HREF="../../stylesheet.css" TITLE="Style"></HEAD><BODY BGCOLOR="white"><!-- ========== START OF NAVBAR ========== --><A NAME="navbar_top"><!-- --></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0"><TR><TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1"><A NAME="navbar_top_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3"> <TR ALIGN="center" VALIGN="top"> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD> <TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="class-use/ArrayList.html"><FONT CLASS="NavBarFont1"><B>Use</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../index-files/index-1.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD> </TR></TABLE></TD><TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM><b>Java<sup><font size=-2>TM</font></sup> 2 Platform<br>Std. Ed. v1.3</b></EM></TD></TR><TR><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../java/util/AbstractSet.html"><B>PREV CLASS</B></A> <A HREF="../../java/util/Arrays.html"><B>NEXT CLASS</B></A></FONT></TD><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../index.html" TARGET="_top"><B>FRAMES</B></A> <A HREF="ArrayList.html" TARGET="_top"><B>NO FRAMES</B></A></FONT></TD></TR><TR><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2"> SUMMARY: INNER | <A HREF="#fields_inherited_from_class_java.util.AbstractList">FIELD</A> | <A HREF="#constructor_summary">CONSTR</A> | <A HREF="#method_summary">METHOD</A></FONT></TD><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">DETAIL: FIELD | <A HREF="#constructor_detail">CONSTR</A> | <A HREF="#method_detail">METHOD</A></FONT></TD></TR></TABLE><!-- =========== END OF NAVBAR =========== --><HR><!-- ======== START OF CLASS DATA ======== --><H2><FONT SIZE="-1">java.util</FONT><BR>Class ArrayList</H2><PRE><A HREF="../../java/lang/Object.html">java.lang.Object</A> | +--<A HREF="../../java/util/AbstractCollection.html">java.util.AbstractCollection</A> | +--<A HREF="../../java/util/AbstractList.html">java.util.AbstractList</A> | +--<B>java.util.ArrayList</B></PRE><DL><DT><B>All Implemented Interfaces:</B> <DD><A HREF="../../java/lang/Cloneable.html">Cloneable</A>, <A HREF="../../java/util/Collection.html">Collection</A>, <A HREF="../../java/util/List.html">List</A>, <A HREF="../../java/io/Serializable.html">Serializable</A></DD></DL><HR><DL><DT>public class <B>ArrayList</B><DT>extends <A HREF="../../java/util/AbstractList.html">AbstractList</A><DT>implements <A HREF="../../java/util/List.html">List</A>, <A HREF="../../java/lang/Cloneable.html">Cloneable</A>, <A HREF="../../java/io/Serializable.html">Serializable</A></DL><P>Resizable-array implementation of the <tt>List</tt> interface. Implements all optional list operations, and permits all elements, including <tt>null</tt>. In addition to implementing the <tt>List</tt> interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent to <tt>Vector</tt>, except that it is unsynchronized.)<p> The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>, <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant time. The <tt>add</tt> operation runs in <i>amortized constant time</i>, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the <tt>LinkedList</tt> implementation.<p> Each <tt>ArrayList</tt> instance has a <i>capacity</i>. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.<p> An application can increase the capacity of an <tt>ArrayList</tt> instance before adding a large number of elements using the <tt>ensureCapacity</tt> operation. This may reduce the amount of incremental reallocation.<p> <strong>Note that this implementation is not synchronized.</strong> If multiple threads access an <tt>ArrayList</tt> instance concurrently, and at least one of the threads modifies the list structurally, it <i>must</i> be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the list. If no such object exists, the list should be "wrapped" using the <tt>Collections.synchronizedList</tt> method. This is best done at creation time, to prevent accidental unsynchronized access to the list: <pre> List list = Collections.synchronizedList(new ArrayList(...)); </pre><p> The iterators returned by this class's <tt>iterator</tt> and <tt>listIterator</tt> methods are <i>fail-fast</i>: if list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.<P><DL><DT><B>Since: </B><DD>1.2</DD><DT><B>See Also: </B><DD><A HREF="../../java/util/Collection.html"><CODE>Collection</CODE></A>, <A HREF="../../java/util/List.html"><CODE>List</CODE></A>, <A HREF="../../java/util/LinkedList.html"><CODE>LinkedList</CODE></A>, <A HREF="../../java/util/Vector.html"><CODE>Vector</CODE></A>, <A HREF="../../java/util/Collections.html#synchronizedList(java.util.List)"><CODE>Collections.synchronizedList(List)</CODE></A>, <A HREF="../../serialized-form.html#java.util.ArrayList">Serialized Form</A></DL><HR><P><!-- ======== INNER CLASS SUMMARY ======== --><!-- =========== FIELD SUMMARY =========== --><A NAME="fields_inherited_from_class_java.util.AbstractList"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor"><TD><B>Fields inherited from class java.util.<A HREF="../../java/util/AbstractList.html">AbstractList</A></B></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><A HREF="../../java/util/AbstractList.html#modCount">modCount</A></CODE></TD></TR></TABLE> <!-- ======== CONSTRUCTOR SUMMARY ======== --><A NAME="constructor_summary"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TD COLSPAN=2><FONT SIZE="+2"><B>Constructor Summary</B></FONT></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../java/util/ArrayList.html#ArrayList()">ArrayList</A></B>()</CODE><BR> Constructs an empty list.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../java/util/ArrayList.html#ArrayList(java.util.Collection)">ArrayList</A></B>(<A HREF="../../java/util/Collection.html">Collection</A> c)</CODE><BR> Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../java/util/ArrayList.html#ArrayList(int)">ArrayList</A></B>(int initialCapacity)</CODE><BR> Constructs an empty list with the specified initial capacity.</TD></TR></TABLE> <!-- ========== METHOD SUMMARY =========== --><A NAME="method_summary"><!-- --></A><TABLE BORDER="1" CELLPADDING="3" CELLSPACING="0" WIDTH="100%"><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TD COLSPAN=2><FONT SIZE="+2"><B>Method Summary</B></FONT></TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#add(int, java.lang.Object)">add</A></B>(int index, <A HREF="../../java/lang/Object.html">Object</A> element)</CODE><BR> Inserts the specified element at the specified position in this list.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> boolean</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#add(java.lang.Object)">add</A></B>(<A HREF="../../java/lang/Object.html">Object</A> o)</CODE><BR> Appends the specified element to the end of this list.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> boolean</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#addAll(java.util.Collection)">addAll</A></B>(<A HREF="../../java/util/Collection.html">Collection</A> c)</CODE><BR> Appends all of the elements in the specified Collection to the end of this list, in the order that they are returned by the specified Collection's Iterator.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> boolean</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#addAll(int, java.util.Collection)">addAll</A></B>(int index, <A HREF="../../java/util/Collection.html">Collection</A> c)</CODE><BR> Inserts all of the elements in the specified Collection into this list, starting at the specified position.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#clear()">clear</A></B>()</CODE><BR> Removes all of the elements from this list.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> <A HREF="../../java/lang/Object.html">Object</A></CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#clone()">clone</A></B>()</CODE><BR> Returns a shallow copy of this <tt>ArrayList</tt> instance.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> boolean</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#contains(java.lang.Object)">contains</A></B>(<A HREF="../../java/lang/Object.html">Object</A> elem)</CODE><BR> Returns <tt>true</tt> if this list contains the specified element.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> void</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#ensureCapacity(int)">ensureCapacity</A></B>(int minCapacity)</CODE><BR> Increases the capacity of this <tt>ArrayList</tt> instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> <A HREF="../../java/lang/Object.html">Object</A></CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#get(int)">get</A></B>(int index)</CODE><BR> Returns the element at the specified position in this list.</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE> int</CODE></FONT></TD><TD><CODE><B><A HREF="../../java/util/ArrayList.html#indexOf(java.lang.Object)">indexOf</A></B>(<A HREF="../../java/lang/Object.html">Object</A> elem)</CODE><BR>⌨️ 快捷键说明
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