How to create a char[] array

Question

I'm trying to allocate a Java char array from Jython which will be populated by a Java library. I want to do the equivalent to from Jython:

char[] charBuffer = new char[charCount];

I've read the documentation for the array and jarray modules (I think they're the same) but I'm not entirely sure which type code I want to use. The two document's seem slightly contradictory, but the newer array module seems more correct. According to the Java documentation, a char is a "16-bit Unicode character" (2 bytes).

So if I check the following type codes:

>>> array.array('c').itemsize # C char, Python character
1
>>> array.array('b').itemsize # C signed char, Python int
1
>>> array.array('B').itemsize # C unsigned char, Python int
2
>>> array.array('u').itemsize # C Py_UNICODE, Python unicode character
4
>>> array.array('h').itemsize # C signed short, Python int
2
>>> array.array('H').itemsize # C unsigned short Python int
4

It seems odd to me that the size of B and H are twice the size of their signed counterparts b and h. Can I safely and reliably use the 16-bit B (unsigned char) or h (signed short int) for a Java char? Or, if using the array module for this is completely wrong for this, please let me know.

Jacob · Accepted Answer · 2014-05-06 01:53:55Z

The short answer is: use 'c'

Under the hood, jython is doing the work of converting data types for you.

You can verify with some tests. There is a class java.nio.CharBuffer with a method wrap() that takes a char[] array. Observe that jython array type 'c' works, while everything else fails:

>>> import array
>>> from java.nio import CharBuffer

>>> array.array('c', 'Hello World')
array('c', 'Hello World')
>>> CharBuffer.wrap( array.array('c', 'Hello World') )
Hello World

>>> array.array('b','Hello World')
array('b', [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100])
>>> CharBuffer.wrap( array.array('b', 'Hello World') )
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: wrap(): 1st arg can't be coerced to char[], java.lang.CharSequence

>>> array.array('u', u'Hello World') 
array('u', u'Hello World')
>>> CharBuffer.wrap( array.array('u', u'Hello World') )
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: wrap(): 1st arg can't be coerced to char[], java.lang.CharSequence

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