Difference between java object and java string

To those who subscribe to all the xxxxxxx-l mailing lists this question
has been cross posted.

I have been slowly but to this point successfully working my way through
using a java API provided by the external party to retrieve a list of
transactions.

Now I am having a problem and most likely it is my lack of java that is
causing it.

What from an ILE RPG perspective is the difference between the following
variable's ?

D stringJ S O Class(*JAVA : 'java.lang.String')
D objectJ S O Class(*JAVA : 'java.lang.Object')

I have a requirement to pass a java.lang.Object to a procedure.

To create a java string I use the makeString procedure.

I can't seem to find a makeObject procedure.

This is the procedure I want to use ...

D getMap PR O CLASS(*JAVA : 'java.lang.Object' )
D EXTPROC(*JAVA : 'java.util.Map' :
D 'get' )
D arg0 O CLASS(*JAVA : 'java.lang.Object' )

D customJ S O Class(*JAVA : 'java.lang.String')

The parameter I need to pass is the name of a custom field that is
returned in the transaction object so I am doing the following ...

customJ = makestring('test_custom_key_1');
stringJ = getMap( JavaMap : customJ );

When the program executes the getMap java blows up and generates a core
dump.

Would appreciate any suggestions or comments to solve the issue as opposed
to totally alternative options/solutions.

Thanks

Don Brown