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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"><html><head><title>VM Spec </title></head><body BGCOLOR=#eeeeff text=#000000 LINK=#0000ff VLINK=#000077 ALINK=#ff0000><table width=100%><tr><td><a href="VMSpecTOC.doc.html">Contents</a> | <a href="Instructions2.doc.html">Prev</a> | <a href="Instructions2.doc2.html">Next</a> | <a href="VMSpecIX.fm.html">Index</a></td><td align=right><i><i>The Java<sup><font size=-2>TM</font></sup> Virtual Machine Specification</i></i></td></tr></table><hr><br> <a href="Instructions2.doc.html">A</a><a href="Instructions2.doc1.html">B</a><a href="Instructions2.doc2.html">C</a><a href="Instructions2.doc3.html">D</a><a href="Instructions2.doc4.html">F</a><a href="Instructions2.doc5.html">G</a><a href="Instructions2.doc6.html">I</a><a href="Instructions2.doc7.html">J</a><a href="Instructions2.doc8.html">L</a><a href="Instructions2.doc9.html">M</a><a href="Instructions2.doc10.html">N</a><a href="Instructions2.doc11.html">P</a><a href="Instructions2.doc12.html">R</a><a href="Instructions2.doc13.html">S</a><a href="Instructions2.doc14.html">T</a><a href="Instructions2.doc15.html">W</a><a name="baload"></a><hr><h2>baload</h2><a name="baload.Operation"></a><p><b>Operation</b><br><blockquote><a name="67301"></a>Load <code>byte</code> or <code>boolean</code> from array<p><Table Border="1"></blockquote><p><b>Format</b><br><blockquote><tr><td><a name="67300"></a> <i>baload</i><td><a name="87568"></a> </Table><br></blockquote><p><a name="baload.Forms"></a><p><b>Forms</b><br><blockquote><a name="67302"></a><i>baload</i> = 51 (0x33)</blockquote><p><a name="baload.Operand"></a><p><b>Operand Stack</b><br><blockquote><a name="67303"></a>..., <i>arrayref</i>, <i>index</i> <img src="chars/arrwdbrt.gif"> ..., <i>value</i></blockquote><p><a name="baload.Description"></a><p><b>Description</b><br><blockquote><a name="67304"></a>The <i>arrayref</i> must be of type <code>reference</code> and must refer to an array whose components are of type <code>byte</code> or of type <code>boolean</code>. The <i>index</i> must be of type <code>int</code>. Both <i>arrayref</i> and <i>index</i> are popped from the operand stack. If the components of the array are of type <code>byte</code>, the component of the array at <i>index</i> is retrieved and sign-extended to an <code>int</code> <i>value</i>. If the components of the array are of type <code>boolean</code>, the component of the array at <i>index</i> is retrieved and zero-extended to an <code>int</code> <i>value</i>. In either case the resulting <i>value</i> is pushed onto the operand stack.</blockquote><p><a name="baload.Runtime"></a><p><b>Runtime Exceptions</b><br><blockquote><a name="67306"></a>If <i>arrayref</i><em> </em>is <code>null</code>, <i>baload</i> throws a <code>NullPointerException</code>. </blockquote><p><blockquote><a name="67307"></a>Otherwise, if <i>index</i> is not within the bounds of the array referenced by <i>arrayref</i>, the <i>baload</i> instruction throws an <code>ArrayIndex</code><code>OutOfBoundsException</code>.</blockquote><p><a name="baload.Notes"></a><p><b>Notes</b><br><blockquote><a name="101054"></a>The <i>baload</i> instruction is used to load values from both <code>byte</code> and <code>boolean</code> arrays. In Sun's implementation of the Java virtual machine, <code>boolean</code> arrays (arrays of type <code>T_BOOLEAN</code>; see <a href="Overview.doc.html#12237">§3.2</a> and the description of the <i>newarray</i> instruction in this chapter) are implemented as arrays of 8-bit values. Other implementations may implement packed <code>boolean</code> arrays; the <i>baload</i> instruction of such implementations must be used to access those arrays.</blockquote><p><a name="bastore"></a><hr><h2>bastore</h2><a name="bastore.Operation"></a><p><b>Operation</b><br><blockquote><a name="67321"></a>Store into <code>byte</code> or <code>boolean</code> array<p><Table Border="1"></blockquote><p><b>Format</b><br><blockquote><tr><td><a name="67320"></a> <i>bastore</i><td><a name="87568"></a> </Table><br></blockquote><p><a name="bastore.Forms"></a><p><b>Forms</b><br><blockquote><a name="67322"></a><i>bastore</i> = 84 (0x54)</blockquote><p><a name="bastore.Operand"></a><p><b>Operand Stack</b><br><blockquote><a name="67323"></a>..., <i>arrayref</i>, <i>index</i>, <i>value</i> <img src="chars/arrwdbrt.gif"> ...</blockquote><p><a name="bastore.Description"></a><p><b>Description</b><br><blockquote><a name="67324"></a>The <i>arrayref</i> must be of type <code>reference</code> and must refer to an array whose components are of type <code>byte</code> or of type <code>boolean</code>. The <i>index</i> and the <i>value</i> must both be of type <code>int</code>. The <i>arrayref</i>, <i>index</i>, and <i>value</i> are popped from the operand stack. If the components of the array are of type <code>byte</code>, the <code>int</code> <i>value</i> is truncated to a <code>byte</code> and stored as the component of the array indexed by <i>index</i>. If the components of the array are of type <code>boolean</code>, the <code>int</code> <i>value</i> is truncated to its low order bit then zero-extended to the storage size for components of <code>boolean</code> arrays used by the implementation. The result is stored as the component of the array indexed by <i>index</i>.</blockquote><p><a name="bastore.Runtime"></a><p><b>Runtime Exceptions</b><br><blockquote><a name="67326"></a>If <i>arrayref</i><em> </em>is <code>null</code>, <i>bastore</i> throws a <code>NullPointerException</code>. </blockquote><p><blockquote><a name="67327"></a>Otherwise, if <i>index</i> is not within the bounds of the array referenced by <i>arrayref</i>, the <i>bastore</i> instruction throws an <code>ArrayIndexOutOfBoundsException</code>.</blockquote><p><a name="bastore.Notes"></a><p><b>Notes</b><br><blockquote><a name="101065"></a>The <i>bastore</i> instruction is used to store values into both <code>byte</code> and <code>boolean</code> arrays. In Sun's implementation of the Java virtual machine, <code>boolean</code> arrays (arrays of type <code>T_BOOLEAN</code>; see <a href="Overview.doc.html#12237">§3.2</a> and the description of the <i>newarray</i> instruction in this chapter) are implemented as arrays of 8-bit values. Other implementations may implement packed <code>boolean</code> arrays; in such implementations the <i>bastore</i> instruction must be able to store <code>boolean</code> values into packed <code>boolean</code> arrays as well as <code>byte</code> values into <code>byte</code> arrays.</blockquote><p><a name="bipush"></a><hr><h2>bipush</h2><a name="bipush.Operation"></a><p><b>Operation</b><br><blockquote><a name="67336"></a>Push <code>byte</code><p><Table Border="1"></blockquote><p><b>Format</b><br><blockquote><tr><td><a name="67333"></a> <i>bipush</i><td><a name="87568"></a> <tr><td><a name="67335"></a> <i>byte</i><td><a name="87568"></a> </Table><br></blockquote><p><a name="bipush.Forms"></a><p><b>Forms</b><br><blockquote><a name="67337"></a><i>bipush</i><em> </em>= 16 (0x10)</blockquote><p><a name="bipush.Operand"></a><p><b>Operand Stack</b><br><blockquote><a name="67338"></a>... <img src="chars/arrwdbrt.gif"> ..., <i>value</i></blockquote><p><a name="bipush.Description"></a><p><b>Description</b><br><blockquote><a name="67339"></a>The immediate <i>byte</i> is sign-extended to an <code>int</code> <i>value</i>. That <i>value</i> is pushed onto the operand stack.</blockquote><p><hr><!-- This inserts footnotes--><p><a href="VMSpecTOC.doc.html">Contents</a> | <a href="Instructions2.doc.html">Prev</a> | <a href="Instructions2.doc2.html">Next</a> | <a href="VMSpecIX.fm.html">Index</a><p><font size="-1"><i>The Java</i><sup><font size=-2>TM</font></sup><i> Virtual Machine Specification </i><br><!-- HTML generated by Suzette Pelouch on March 30, 1999 --><i><a href="Copyright.doc.html">Copyright © 1999 Sun Microsystems, Inc.</a>All rights reserved</i><br>Please send any comments or corrections to <a href="mailto:jvm@java.sun.com">jvm@java.sun.com</a></font></body></html>⌨️ 快捷键说明
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