com.heirloomcomputing.epli.runtime

Class Union<T>

java.lang.Object

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

public class Union<T>
extends java.lang.Object

Simulates the PL/I UNION, which overlays one object with another by making immutable Java wrapper classes (Integer, String) and Elastic PL/I classes (FixedBin, Complex) both mutable and sharable. So, two Groups that contain similar elements are defined as containing those elements of type Union instead of Integer. When the same Union instance is included in each Group structure (under different element names within those structures) they are essentially sharing the underlying object. if one is changed, so is the other. Use get() and set() method to access or mutate (change) the underlying object value instead of assignment statements. The Elastic PL/I compiler detects when UNIONs or BASED(ADDR(anotherGroup)) concepts are employed to implicitly share two structures.

PL/I code

   DCL 1 A,
         2 B FIXED BIN(15)
         2 C FIXED BIN(31)
         2 D CHAR(10);
   DCL 1 W BASED(ADDR(A)),
         2 X FIXED BIN(15)
         2 Y FIXED BIN(31)
         2 Z CHAR(10);
   A.C = 11;
   W.Y = 22;
   IF A.C = W.Y THEN PUT SKIP LIST('CORRECT');
   ELSE PUT SKIP LIST('INCORRECT');
 

Java code

   class A extends Group {
         @OFF(0) Union b = new Union(short)0);
         @OFF(2) Union c = new Union((int)0);
         @OFF(6) @CHAR(10) Union d = new Union("          ");
   }
   A a = new A();
   class W extends Group {
         @OFF(0) Union x = a.b;
         @OFF(2) Union y = a.c;
         @OFF(6) @CHAR(10) Union z = a.z;
   }
   a.c.set(11);
   W w = new W();
   w.y.set(22);
   if (a.c.get() = w.y.get()) {
       System.out.println();
       System.out.println("CORRECT");
   } else {
       System.out.println();
       System.out.println("INCORRECT");
   }
 

Or a single structure (or fields or variables) which are UNIONs or contain UNIONs of one or more elements

PL/I code

      DCL 1 G,
            2 H FIXED BIN(15),
            2 I UNION,
              3 I1 FIXED BIN(31),
              3 I2 FIXED BIN(31),
            2 J CHAR(10)

      // set the two elements to different values but because they are
      // shared they should be the same (last set) value
      G.I1 = 77;
      G.I2 = 88;
      IF I1 = I2 THEN PUT SKIP LIST('CORRECT');
      ELSE PUT SKIP LIST('INCORRECT');
 

Java code

      class G extends Group {
          @OFF(0) Short h = Short.valueOf((short) 0);
          @OFF(2) Union i1 = (new Union()).set((int) 0);
          @OFF(2) Union i2 = i1;
          @OFF(6) @CHAR(10) String j = new String("          ");
      }
      G g = new G();

      // set the two elements to different values but because they are
      // shared they should be the same (last set) value
      g.i1.set((int) 77);
      g.i2.set((int) 88);
      if (g.i1.get() == g.i2.get()) {
          System.out.println();
          System.out.print("CORRECT");
      } else {
          System.out.println();
          System.out.print("INCORRECT");
      }

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
protected int	len
protected int	off
protected T	ref the Object to which this Union refers
protected Union<T>	uni share a byte-range of another object

Constructor Summary

Constructors

Constructor and Description
Union() Construct a null Union
Union(T ref) Construct a Union referencing another object
Union(Union<T> uni, int off, int len) Construct a Union referencing another union's byte range

Method Summary

Modifier and Type	Method and Description
Union<T>	fromBytes(byte[] bytes) turn a sequence of bytes into a Union
T	get() Return the underlying shared object of this Union
static void	main(java.lang.String[] args) Union unit test
Union<T>	set(T obj) set the underlying shared object of this Union
byte[]	toBytes() turn a shared object of the Union into a sequence of bytes
java.lang.String	toString() convert the underlying object to a string

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

ref

protected T ref

the Object to which this Union refers

uni

protected Union<T> uni

share a byte-range of another object

off

protected int off

len

protected int len

Constructor Detail

Union

public Union()

Construct a null Union

Union

public Union(T ref)

Construct a Union referencing another object

Union

public Union(Union<T> uni,
             int off,
             int len)

Construct a Union referencing another union's byte range

Method Detail

get

public T get()

Return the underlying shared object of this Union

Returns:

the object reference this UNION is for

Throws:

CONDITION - for NULLPOINTER if this Union was never set

set

public Union<T> set(T obj)

set the underlying shared object of this Union

Parameters:

obj - of type T to set this shared object

Returns:

this union so it can be chained with other operations like assignment

toBytes

public byte[] toBytes()

turn a shared object of the Union into a sequence of bytes

Returns:

byte array of the Union's shared object

Throws:

CONDITION - for NULLPOINTER if this Union was never set

fromBytes

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

turn a sequence of bytes into a Union

Parameters:

bytes - - sequence of bytes representing a Union

Returns:

this Union to facilitate potential chaining

Throws:

CONDITION - for NULLPOINTER if this Union was never set

toString

public java.lang.String toString()

convert the underlying object to a string

Overrides:

toString in class java.lang.Object

Returns:

the toString() of the union's underlying object

Throws:

CONDITION - for NULLPOINTER if this Union was never set

main

public static void main(java.lang.String[] args)

Union unit test