Donut  |  1.6_r1
Html程序  |  110行  |  2.44 KB 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html>

<head>
<title>iget&lt;kind&gt;</title>
<link rel=stylesheet href="opcode.css">
</head>

<body>

<h1>iget&lt;kind&gt;</h1>

<h2>Purpose</h2>

<p>
Perform the identified object instance field operation with the identified
field, loading or storing into the value register.
</p>
<p>
Note: These opcodes are reasonable candidates for static linking, altering the
field argument to be a more direct offset.
</p>

<h2>Details</h2>

<table class="instruc">
<thead>
<tr>
  <th>Op &amp; Format</th>
  <th>Mnemonic / Syntax</th>
  <th>Arguments</th>
</tr>
</thead>
<tbody>
<tr>
  <td>52..58 22c</td>
  <td>i<i>instanceop</i> vA, vB, field@CCCC<br/>
    52: iget<br/>
    53: iget-wide<br/>
    54: iget-object<br/>
    55: iget-boolean<br/>
    56: iget-byte<br/>
    57: iget-char<br/>
    58: iget-short<br/>
  </td>
  <td><code>A:</code> dest value register or pair; (4 bits)<br/>
    <code>B:</code> object register (4 bits)<br/>
    <code>C:</code> instance field reference index (16 bits)</td>
</tr>
</tbody>
</table>

<h2>Constraints</h2>

<ul>
  <li>
    A and B must be valid register indices in the current stackframe.
  </li>
  <li>
    For the -wide variant, also A+1 must be a valid register index in the
    current stackframe.
  </li>
  <li>
    Register vB must contain an object reference.
  </li>
  <li>
    C must be a valid index into the field reference pool.
  </li>
  <li>
    The field must be an instance field. The type of the field denoted by C must
    match the variant of the instruction.
  </li>
</ul>

<h2>Behavior</h2>

<ul>
  <li>
    The value of the given instance field is read from the given object and
    moved into the given register vA, that is, vA'=&lt;object&gt;.&lt;field&gt;.
  </li>
  <li>
    If v(A-1) is the lower half of a register pair, v(A-1)' becomes undefined.
  </li>
    <li>For all but the -wide variant, if v(A+1) is the upper half of a register
    pair, v(A+1)' becomes undefined.
  </li>
  <li>
    For the -wide variant, if v(A+2) is the upper half of a register pair,
    v(A+2)' becomes undefined.
  </li>
</ul>

<h2>Exceptions</h2>

<ul>
  <li>
    NullPointerException if object is null.
  </li>
  <li>
    IllegalAccessException if &lt;object&gt;.&lt;field&gt; is not visible from
    the current context according to the usual visibility and access rules of
    the Java programming language.
  </li>
</ul>

</body>
</html>