com.heirloomcomputing.epli.runtime

Class Offset<T>

java.lang.Object

com.heirloomcomputing.epli.runtime.Pointer<T>

com.heirloomcomputing.epli.runtime.Offset<T>

All Implemented Interfaces:

java.lang.Comparable<Pointer<T>>

public class Offset<T>
extends Pointer<T>

Simulates the PL/I OFFSET, which can reference any object within an Area. Offsets can be typed, e.g., Offset<FixedBin> or Offset<MyLevel1>, or generic, e.g, Offset<Object> or Offset<?>. The epli compiler may produce generic offsets with their contents known to be specific in which case Java casts are used to "dereference". The ref() method is used to "dereference" an Offset. Dereferencing NULL offsets will throw the NULLPOINTER ERROR Condition. PL/I OFFSETs when generated as Java Offsets hold references to standard Java objects allocated on the Java heap but are associated with an Area to use that class's facilities to marshal and un-marshal associated objects "within" Area for I/O operations. It has less to do with actually allocating the alloted space defined for an Area.

PL/I code

   DCL A AREA(32000);
   DCL O OFFSET(A);
   DCL 1 W BASED(O),
         2 X FIXED BIN(15)
         2 Y FIXED BIN(31)
         2 Z CHAR(10);
   ALLOCATE W IN(A) SET(O);
   O->Y = 11;
 

Java code

   class W extends Group {
         @OFFSET(0) x Short = new Short((short)0);
         @OFFSET(2) y Integer = new Integer((int)0);
         @OFFSET(6) @CHAR(10) z String = new String("          ");
   }
   Area a = new Area("A", 32000);
   Offset<A> o = new Offset<A>(new W(), a);
   o.ref() = 11;
 

This is a wrapper class of either a specific or generic object class primarily to cover throw the PL/I NULLPOINTER ERROR Condition instead of Java NullPointerException

Author:

Heirloom Computing, Inc.

Field Summary

Fields

Modifier and Type	Field and Description
static int	BYTES size in bytes if converted to a byte array
static Offset<java.lang.Object>	NULL an undefined OFFSET

Fields inherited from class com.heirloomcomputing.epli.runtime.Pointer

model, ref

Constructor Summary

Constructors

Constructor and Description
Offset(T ref, Area inArea) Construct an Offset referencing another object in an area

Method Summary

Modifier and Type	Method and Description
void	free() Invalidate the offset reference.
void	free(boolean ignore) Invalidate the offset reference ignoring invalid Offsets.
Pointer<T>	fromBytes(byte[] bytes) turn a sequence of bytes into a Pointer
byte[]	toBytes() turn a Pointer into a sequence of bytes

Methods inherited from class com.heirloomcomputing.epli.runtime.Pointer

assign, assign, assign, assign, compareTo, equal, handle, isNull, main, model, ref, ref, ref, refAssign, toString, typeof

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

BYTES

public static final int BYTES

size in bytes if converted to a byte array

See Also:

Constant Field Values

NULL

public static final Offset<java.lang.Object> NULL

an undefined OFFSET

Constructor Detail

Offset

public Offset(T ref,
              Area inArea)

Construct an Offset referencing another object in an area

Parameters:

ref - - the reference to another object

inArea - - the Area the Offset is within

Method Detail

free

public void free()

Invalidate the offset reference. Removing all references to an Area will cause the Java JVM to remove it

Overrides:

free in class Pointer<T>

free

public void free(boolean ignore)

Invalidate the offset reference ignoring invalid Offsets. Removing all references to an Area will cause the Java JVM to remove it

Overrides:

free in class Pointer<T>

Parameters:

ignore - - ignore any prior freed pointers (free() is a no-op)

toBytes

public byte[] toBytes()

turn a Pointer into a sequence of bytes

Overrides:

toBytes in class Pointer<T>

Returns:

byte array of the Pointer turned into a sequence of bytes

fromBytes

public Pointer<T> fromBytes(byte[] bytes)

turn a sequence of bytes into a Pointer

Overrides:

fromBytes in class Pointer<T>

Parameters:

bytes - - sequence of bytes representing a Pointer

Returns:

Pointer that was previously Remembered by toBytes()

Throws:

ERROR - CONDITION if the bytes don't represent a Pointer previously Remembered in this JVM