Java bytecode: Difference between revisions

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The '''Java byte-code''' is the form of instructions that the [[Java virtual machine]] executes. Each byte-code instruction is one byte in length (hence the name), thus the number of byte-codes is limited to no more than 256. Not all 256 possible byte-code values are used, in fact [[Sun Microsystems]], the original cretorscreators of the [[Java programming language]], the [[Java virtual machine]] and other components of the Java Runtime Envirnoment, have permenently set aside a fewnumber of values to be permenently unimplemented. A list of theThe bytecodes isare given below.

===The Java byte-codes===

<table>

<tr><td>Mneumonic''Mnemonic''<tt>&nbsp;&nbsp;&nbsp;&nbsp;</tt><td><center><tt>&nbsp;&nbsp;</tt>''Opcode'' (in hex)<tt>&nbsp;&nbsp;&nbsp;&nbsp;</tt></center><td>''Description''

<tr><td><td><tdbr>

<tr><td><tt>aaload</tt><td><center>32</center><td>loads onto the stack a reference to an array

<tr><td><tt>aastore</tt><td><center>53</center><td>stores into a reference to an array

<tr><td><tt>aconst_null</tt><td><center>01</center><td>pushes a ''null'' reference onto the stack

<tr><td><tt>aload</tt><td><center>19</center><td>loads a refernce onto the stack from a local variable

<tr><td><tt>aload_0</tt><td><center>2a</center><td>loads a refernece from local variable 0

<tr><td><tt>aload_1</tt><td><center>2b</center><td>loads a refernece from local variable 1

<tr><td><tt>aload_2</tt><td><center>2c</center><td>loads a refernece from local variable 2

<tr><td><tt>aload_3</tt><td><center>2d</center><td>loads a refernece from local variable 3

<tr><td><tt>anewarray</tt><td><center>bd</center><td>creates a new array of references

<tr><td><tt>areturn</tt><td><center>b0</center><td>returns a reference from a method

<tr><td><tt>arraylength</tt><td><center>be</center><td>gets the length of an array

<tr><td><tt>astore</tt><td><center>3a</center><td>stores a reference into a local variable

<tr><td><tt>astore_0</tt><td><center>4b</center><td>stores a reference into local variable 0

<tr><td><tt>astore_1</tt><td><center>4c</center><td>stores a reference into local variable 1

<tr><td><tt>astore_2</tt><td><center>4d</center><td>stores a reference into local variable 2

<tr><td><tt>astore_3</tt><td><center>4e</center><td>stores a reference into local variable 3

<tr><td><tt>athrow</tt><td><center>bf</center><td>throws an error or exception

<tr><td><br>

<tr><td><tt>baload</tt><td><center>33</center><td>loads a byte or boolean value from an array

<tr><td><tt>bastore</tt><td><center>54</center><td>stores a byte or boolean value into an array

<tr><td><tt>bipush</tt><td><center>10</center><td>pushes a byte onto the stack

<tr><td><br>

<tr><td><tt>caload</tt><td><center>34</center><td>loads a char from an array

<tr><td><tt>castore</tt><td><center>55</center><td>stores a char into an array

<tr><td><tt>checkcast</tt><td><center>c0</center><td>checks whether an object is of a certain type

<tr><td><br>

<tr><td><tt>d2f</tt><td><center>90</center><td>converts a double to a float

<tr><td><tt>d2i</tt><td><center>8e</center><td>converts a double to an int

<tr><td><tt></tt><td><center></center><td>

</table>

more to be added later

==External links==

*[http://java.sun.com/docs/books/vmspec/2nd-edition/html/VMSpecTOC.doc.html Sun's Java Virtual Machine Specification]