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A Java virtual machine instruction consists of an opcode specifying the operation to be performed, f

All <code>constant_pool</code> table entries have the following general format:<p>
<pre><br><a name="9604"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>cp_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 info[];
</code><a name="9689"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br></pre><a name="86988"></a>
Each item in the <code>constant_pool</code> table must begin with a 1-byte tag indicating the 
kind of <code>cp_info</code> entry. The contents of the <code>info</code> array vary with the value of <code>tag</code>. 
The valid tags and their values are listed in <a href="ClassFile.doc.html#87125">Table 4.3</a>. Each tag byte must be followed by two or more bytes giving information about the specific constant. The format
of the additional information varies with the tag value.<p><Table Border="1">
<tr><th><b><i>Constant Type
</i></b>
<th><b><i>Value
</i></b>
<tr><td><a name="87125"></a>
<code>CONSTANT_Class</code>
<td><a name="87127"></a>
<code>7</code>

<tr><td><a name="87129"></a>
<code>CONSTANT_Fieldref</code>
<td><a name="87131"></a>
<code>9</code>

<tr><td><a name="87133"></a>
<code>CONSTANT_Methodref</code>
<td><a name="87135"></a>
<code>10</code>

<tr><td><a name="87137"></a>
<code>CONSTANT_InterfaceMethodref</code>
<td><a name="87139"></a>
<code>11</code>

<tr><td><a name="87141"></a>
<code>CONSTANT_String</code>
<td><a name="87143"></a>
<code>8</code>

<tr><td><a name="87145"></a>
<code>CONSTANT_Integer</code>
<td><a name="87147"></a>
<code>3</code>

<tr><td><a name="87149"></a>
<code>CONSTANT_Float</code>
<td><a name="87151"></a>
<code>4</code>

<tr><td><a name="87153"></a>
<code>CONSTANT_Long</code>
<td><a name="87155"></a>
<code>5</code>

<tr><td><a name="87157"></a>
<code>CONSTANT_Double</code>
<td><a name="87159"></a>
<code>6</code>

<tr><td><a name="87161"></a>
<code>CONSTANT_NameAndType</code>
<td><a name="87163"></a>
<code>12</code>

<tr><td><a name="87165"></a>
<code>CONSTANT_Utf8</code>
<td><a name="87167"></a>
<code>1</code>

</Table><br><br>
<p><a name="1221"></a>
<h3>4.4.1    The <code>CONSTANT_Class_info</code> Structure</h3>
<a name="1222"></a>
The <code>CONSTANT_Class_info</code> structure is used to represent a class or an interface:
<p><pre><br><a name="1223"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>CONSTANT_Class_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 name_index;
</code><a name="1226"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br></pre><a name="9357"></a>
The items of the <code>CONSTANT_Class_info</code> structure are the following:
<p><a name="1228"></a>
<dl><dt><code>tag</code>
<dd> The <code>tag</code> item has the value <code>CONSTANT_Class</code> (<code>7</code>).<p>
<a name="8829"></a>
<dt><code>name_index</code>
<dd> The value of the <code>name_index</code> item must be a valid index into the <code>constant_pool</code> table. The <code>constant_pool</code> entry at that index must be a <code>CONSTANT_Utf8_info</code> <a href="ClassFile.doc.html#7963">(&#167;4.4.7)</a> structure representing a valid fully qualified class or interface name <a href="Concepts.doc.html#20389">(&#167;2.8.1)</a> encoded in internal form (<a href="ClassFile.doc.html#14757">&#167;4.2)</a>. <p>
</dl>
<a name="84853"></a>
 <p>
<a name="1232"></a>
Because arrays are objects, the opcodes <i>anewarray</i> and <i>multianewarray</i> can reference array "classes" via <code>CONSTANT_Class_info</code> <a href="ClassFile.doc.html#1221">(&#167;4.4.1)</a> structures in the <code>constant_pool</code> table. For such array classes, the name of the class is the descriptor of the array type. For example, the class name representing a two-dimensional <code>int</code> array type<p>
<pre>&nbsp;&nbsp;&nbsp;&nbsp;<code>int[][] 
</code></pre><a name="1234"></a>
is 
<p><pre>&nbsp;&nbsp;&nbsp;&nbsp;<code>[[I
</code></pre><a name="1237"></a>
The class name representing the type array of class <code>Thread
</code><p><pre>&nbsp;&nbsp;&nbsp;&nbsp;<code>Thread[] 
</code></pre><a name="1239"></a>
is 
<p><pre>&nbsp;&nbsp;&nbsp;&nbsp;<code>[Ljava/lang/Thread;
</code></pre><a name="42039"></a>
An array type descriptor is valid only if it represents 255 or fewer dimensions.
<p><a name="42041"></a>
<h3>4.4.2    The <code>CONSTANT_Fieldref_info</code>, <code>CONSTANT_Methodref_info</code>, and <code>CONSTANT_InterfaceMethodref_info</code> Structures</h3>
<a name="1253"></a>
Fields, methods, and interface methods are represented by similar structures:
<p><pre><br><a name="1254"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>CONSTANT_Fieldref_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 class_index;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 name_and_type_index;
</code><a name="1258"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br><br><a name="1260"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>CONSTANT_Methodref_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 class_index;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 name_and_type_index;
</code><a name="1264"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br><br><a name="1266"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>CONSTANT_InterfaceMethodref_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 class_index;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 name_and_type_index;
</code><a name="1270"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br></pre><a name="9360"></a>
The items of these structures are as follows:
<p><a name="6689"></a>
<dl><dt><code>tag</code>
<dd>The <code>tag</code> item of a <code>CONSTANT_Fieldref_info</code> structure has the value <code>CONSTANT_Fieldref</code> (<code>9</code>). <p>
The <code>tag</code> item of a <code>CONSTANT_Methodref_info</code> structure has the value <code>CONSTANT_Methodref</code> (<code>10</code>).<p>

The <code>tag</code> item of a <code>CONSTANT_InterfaceMethodref_info</code> structure has the value <code>CONSTANT_InterfaceMethodref</code> (<code>11</code>).<p>
<a name="1273"></a>
<dt><code>class_index</code>
<dd> The value of the <code>class_index</code> item must be a valid index into the <code>constant_pool</code> table. The <code>constant_pool</code> entry at that index must be a <code>CONSTANT_Class_info</code> <a href="ClassFile.doc.html#1221">(&#167;4.4.1)</a> structure representing the class or interface type that contains the declaration of the field or method.<p>

The <code>class_index</code> item of a <code>CONSTANT_Methodref_info</code> structure must be a class type, not an interface type. The <code>class_index</code> item of a <code>CONSTANT_InterfaceMethodref_info</code> structure must be an interface type. The <code>class_index</code> item of a <code>CONSTANT_Fieldref_info</code> structure may be either a class type or an interface type. <p>
<a name="1276"></a>
<dt><code>name_and_type_index</code>
<dd> The value of the <code>name_and_type_index</code> item must be a valid index into the <code>constant_pool</code> table. The <code>constant_pool</code> entry at that index must be a <code>CONSTANT_NameAndType_info</code> <a href="ClassFile.doc.html#1327">(&#167;4.4.6)</a> structure. This <code>constant_pool</code> entry indicates the name and descriptor of the field or method. In a <code>CONSTANT_Fieldref_info</code> the indicated descriptor must be a field descriptor <a href="ClassFile.doc.html#14152">(&#167;4.3.2)</a>. Otherwise, the indicated descriptor must be a method descriptor <a href="ClassFile.doc.html#7035">(&#167;4.3.3)</a>.<p>

If the name of the method of a <code>CONSTANT_Methodref_info</code> structure begins with a<code>'  &lt;'</code> (<code>'\u003c'</code>), then the name must be the special name <code>&lt;init&gt;</code>, representing an instance initialization method <a href="Overview.doc.html#12174">(&#167;3.9)</a>. Such a method must return no value. <p>
</dl>
<a name="29297"></a>
<h3>4.4.3    The <code>CONSTANT_String_info</code> Structure</h3>
<a name="21417"></a>
The <code>CONSTANT_String_info</code> structure is used to represent constant objects of the 
type <code>String</code>:
<p><pre><br><a name="21424"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>CONSTANT_String_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u2 string_index;
</code><a name="21426"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br></pre><a name="9366"></a>
The items of the <code>CONSTANT_String_info</code> structure are as follows:
<p><a name="21646"></a>
<dl><dt><code>tag</code></b><br><a name="21647"></a>
<dd> The <code>tag</code> item of the <code>CONSTANT_String_info</code> structure has the value <code>CONSTANT_String</code> (<code>8</code>).<p>
<a name="6663"></a>
<dt><code>string_index</code></b><br><a name="6664"></a>
<dd> The value of the <code>string_index</code> item must be a valid index into the <code>constant_pool</code> table. The <code>constant_pool</code> entry at that index must be a <code>CONSTANT_Utf8_info</code> <a href="ClassFile.doc.html#7963">(&#167;4.4.7)</a> structure representing the sequence of characters to which the <code>String</code> object is to be initialized.<p>
<a name="21942"></a>
</dl>
<h3>4.4.4    The <code>CONSTANT_Integer_info</code> and <code>CONSTANT_Float_info</code> Structures </h3>
<a name="20768"></a>
The <code>CONSTANT_Integer_info</code> and <code>CONSTANT_Float_info</code> structures represent 
4-byte numeric (<code>int</code> and <code>float</code>) constants:
<p><pre><br><a name="20560"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>CONSTANT_Integer_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u4 bytes;
</code><a name="20497"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br><br><a name="20499"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>CONSTANT_Float_info {
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u1 tag;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	u4 bytes;
</code><a name="9373"></a>&nbsp;&nbsp;&nbsp;&nbsp;<code>}
</code><br></pre><a name="9376"></a>
The items of these structures are as follows:
<p><a name="9375"></a>
<dl><dt><code>tag</code>
<dd> The <code>tag</code> item of the <code>CONSTANT_Integer_info</code> structure has the value <code>CONSTANT_Integer</code> (<code>3</code>).<p>

The <code>tag</code> item of the <code>CONSTANT_Float_info</code> structure has the value <code>CONSTANT_Float</code> (<code>4</code>).<p>
<a name="20502"></a>
<dt><code>bytes</code>
<dd> The <code>bytes</code> item of the <code>CONSTANT_Integer_info</code> structure represents the value of the <code>int</code> constant. The bytes of the value are stored in big-endian (high byte first) order.<p>

The <code>bytes</code> item of the <code>CONSTANT_Float_info</code> structure represents the value of the <code>float</code> constant in IEEE 754 floating-point single format <a href="Overview.doc.html#28147">(&#167;3.3.2)</a>. The bytes of the single format representation are stored in big-endian (high byte first) order. <p>

The value represented by the <code>CONSTANT_Float_info</code> structure is determined as follows. The bytes of the value are first converted into an <code>int</code> constant bits. Then:<p>
<ul>
<li>If bits is <code>0x7f800000</code>, the <code>float</code> value will be positive infinity.
<li>If bits is <code>0xff800000</code>, the <code>float</code> value will be negative infinity.
<li>If bits is in the range <code>0x7f800001</code> through <code>0x7fffffff</code> or in the range <code>0xff800001</code> through <code>0xffffffff</code>, the <code>float</code> value will be NaN. 
<li>In all other cases, let <code>s</code>, <code>e</code>, and <code>m</code> be three values that might be computed from <em>bits</em>:
</ul><pre>&nbsp;&nbsp;&nbsp;&nbsp;<code>	int s = ((</code>bits<code> &gt;&gt; 31) == 0) ? 1 : -1;
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	int e = ((</code>bits<code> &gt;&gt; 23) &amp; 0xff);
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>	int m = (e == 0) ?
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>			(</code>bits<code> &amp; 0x7fffff) &lt;&lt; 1 :
</code>&nbsp;&nbsp;&nbsp;&nbsp;<code>			(</code>bits<code> &amp; 0x7fffff) | 0x800000;
</code>
Then the <code>float</code> value equals the result of the mathematical expression <code>s&#183;m&#183;2<sup>e-150</sup></code>.
</ul></pre><a name="1348"></a>
<h3>4.4.5    The <code>CONSTANT_Long_info</code> and <code>CONSTANT_Double_info</code> Structures</h3>
<a name="20772"></a>
The <code>CONSTANT_Long_info</code> and <code>CONSTANT_Double_info</code> represent 8-byte 
numeric (<code>long</code> and <code>double</code>) constants: