Data Types in JVM COBOL

COBOL provides predefined usages corresponding to many of the most commonly used JVM types. These names can be used when declaring a data item, and anywhere a type specifier is expected - see Specifying Type Names. For example:

    01 anInteger binary-long.

Predefined JVM Types

.NET or JVM COBOL	.NET type	JVM type	C# keyword	Description
Integer types:
binary-char	System.SByte	byte	sbyte	An 8-bit signed integer Not CLS-compliant
binary-char unsigned	System.Byte		byte	An 8-bit unsigned integer
binary-short	System.Int16	short	short	A 16-bit signed integer Not CLS-compliant
binary-short unsigned	System.UInt16		ushort	A 16-bit unsigned integer
binary-long	System.Int32	int	int	A 32-bit signed integer
binary-long unsigned	System.UInt32		uint	A 32-bit unsigned integer Not CLS-compliant.
binary-double	System.Int64	long	long	A 64-bit signed integer
binary-double unsigned	System.UInt64		ulong	A 64-bit unsigned integer Not CLS-compliant
Floating point types:
float-short	System.Single	float	float	A single-precision (32-bit) floating-point number
float-long	System.Double	double	double	A double-precision (64-bit) floating-point number
Logical types:
condition-value	System.Boolean	boolean	bool	A boolean value (true or false)
Other types:
character	System.Char	char	char	A unicode (16-bit) character
decimal	System.Decimal	see JVMDECIMAL.	decimal	A 96-bit decimal value
Class objects:
object	System.Object	java.lang.Object	object	The root of the object hierarchy
string	System.String	java.lang.String	string	An immutable, fixed-length string of Unicode characters
Collection types:
list	System.Collections.Generic.IList<T>	java.util.List		An ordered collection of items
dictionary	System.Collections.Generic.IDictionary<TKey, TValue>	java.util.Map		A mapping of keys to values
set	System.Collections.Generic.ISet<T>	java.util.Set<T>		An unordered collection of items

Referencing Types Using the TYPE Keyword

Further managed types can be specified in COBOL using the syntax TYPE classname in the data item definition. For example:

    01 objMyType type MyType.

All the COBOL data types in the table above and any further JVM types that you define are mapped onto the corresponding native type (.NET or JVM), but they must conform to the following rules. They:

Must be declared at 01 (or 77) level
Must have no REDEFINES or RENAMES
Must never be the subject of reference modification
Must never be the subject of the ADDRESS OF clause
May use format 3 of the OCCURS clause to declare an array

Any COBOL data item that does not follow these rules, or is of any other category, is not considered to be a native type (.NET or JVM) and is allocated by the Compiler within an internally managed byte array. COBOL pointer data items always point into one of these byte arrays.

Resolving Types

If your code references a type without specifying the namespace it belongs to, the Compiler first attempts to resolve this to a type formed by adding the namespace of the current class to the type name. For example:

$set ilusing"System"
class-id MyNamespace.EventHandler.
01 o type EventHandler.                       
end class.

In the example above 01 o type EventHandler. resolves to MyNamespace.EventHandler and not to System.EventHandler.

If no such type exists then the Compiler tries to resolve the unspecified type in the order listed below:

if the current compilation includes a single type with this name and with no namespace, the Compiler resolves it to this type.
if a referenced assembly includes a single type with the same name and with no namespace, the Compiler resolves to this type.
if the current compilation includes a single type with this name and with the same namespace as the current type, the Compiler resolves it to this type
if a referenced assembly includes a single type with this name and with the same namespace as the current type, the Compiler resolves it to this type
if among the namespaces specified with the ILUSING directives a single type with the same name, the Compiler resolves to this type.
if among the namespaces specified with the ILUSING directives there are more than one namespaces that include the same type, the Compiler emits an error.

Value Types, Reference Types and Boxing

JVM COBOL distinguishes between:

Value types (such as binary-long and System.DateTime in .NET). Value type data items contain the actual data. For example, a COBOL binary-long data item contains a 32 bit integer.
Reference types, which are allocated on the object heap. Reference type data items hold a reference into the object heap. Reference types are under the management of the garbage collector.

All value types can be turned into reference types by a process known as boxing. For example, you can set an object reference to a value type, such as a binary-long.

Boxing happens automatically when needed, for example when a value type is passed as a parameter to a method that expects an object as a parameter.

You can box explicitly by assigning a value type to a generic object (such as System.Object in .NET COBOL or java.lang.Object in JVM COBOL).

You can unbox value types to restore the original value type.

When you specify TYPE classname in the data item definition:

If classname represents a reference type, you get a reference type object.
If classname represents a value type, you get a value type object.

During boxing, the system copies the value into the object heap and returns a reference to it. When the reference is no longer active (because nothing in the program is holding on to it), the space in the object heap will eventually be regained by the garbage collector.

See the ValueTypes sample, available from