/**
* Read an instruction from (byte code) input stream and return the appropiate object.
*
* @param file file to read from
* @return instruction object being read
*/
public static final Instruction readInstruction(ByteSequence bytes) throws IOException {
boolean wide = false;
short opcode = (short) bytes.readUnsignedByte();
Instruction obj = null;
if (opcode == Constants.WIDE) { // Read next opcode after wide byte
wide = true;
opcode = (short) bytes.readUnsignedByte();
}
if (InstructionConstants.INSTRUCTIONS[opcode] != null)
return InstructionConstants.INSTRUCTIONS[
opcode]; // Used predefined immutable object, if available
/* Find appropiate class, instantiate an (empty) instruction object
* and initialize it by hand.
*/
Class clazz;
try {
clazz = Class.forName(className(opcode));
} catch (ClassNotFoundException cnfe) {
// If a class by that name does not exist, the opcode is illegal.
// Note that IMPDEP1, IMPDEP2, BREAKPOINT are also illegal in a sense.
throw new ClassGenException("Illegal opcode detected.");
}
try {
obj = (Instruction) clazz.newInstance();
if (wide
&& !((obj instanceof LocalVariableInstruction)
|| (obj instanceof IINC)
|| (obj instanceof RET))) throw new Exception("Illegal opcode after wide: " + opcode);
obj.setOpcode(opcode);
obj.initFromFile(bytes, wide); // Do further initializations, if any
// Byte code offset set in InstructionList
} catch (Exception e) {
throw new ClassGenException(e.toString());
}
return obj;
}
/** Read needed data (e.g. index) from file. */
protected void initFromFile(ByteSequence bytes, boolean wide) throws IOException {
length = 3;
b = bytes.readShort();
}