MATLAB: Does the Hashtable with string keys not work as expected in MATLAB

hashmapjava.lang.objectkeymapMATLABtable

I have the following code in Java:

Hashtable hash =new Hashtable();
hash.put("a", "aa");
hash.put("b", "bb");

I then pass that object back to MATLAB and try to access those elements in the Hashtable:

hash
a=hash.get('a')
b=hash.get('b')
hash.put('d','dddddd');

Best Answer

This is due to how MATLAB converts the strings to Java Objects.

The workaround is to explicitly convert the MATLAB strings to the java.lang.String class.

Related Solutions

MATLAB: Do I receive a “java.lang.OutOfMemoryError: Java heap space” error after upgrading to Database Toolbox 3.5.1 (R2009a)

In Database Toolbox 3.5.1 (R2009a) the default value of the JDBC property 'defaultRowPrefetch' was changed from 10 to 10000. This change should increase the performance of the toolbox, however it will also increase the memory requirements of the toolbox.

To prevent the out of memory error from occuring, you can change this property back to its default value; below instructions for this are given for different versions of the toolbox:

To change the property in Database Toolbox 3.5.1 (R2009a):

After creating the connection:

conn = database(....);

Run the following code:

h = conn.Handle;
h.setDefaultRowPrefetch(10);

To change the property in Database Toolbox 3.6 (R2009b):

Run the following code:

setdbprefs('DefaultRowPrefetch','10')

MATLAB: Converting Hashtables with Matlab

Hopefully this example helps to explain. You can obviously skip over the creating bit as you already have a table and presumably you just want to get all of the values out of it.

% create example Java hashtable and add some key/value pairs
h = java.util.Hashtable;
h.put('Name', 'John');
h.put('Country', 'UK');
% retrieve the value for a specific key
h.get('Name');
% retrieve all key names
allKeys = arrayfun(@char, h.keySet.toArray, 'UniformOutput', false);
% retrieve all key values
allValues = cellfun(@(x) h.get(x), allKeys, 'UniformOutput', false);

Best Answer

Related Solutions

MATLAB: Do I receive a “java.lang​.OutOfMemo​ryError: Java heap space” error after upgrading to Database Toolbox 3.5.1 (R2009a)

MATLAB: Converting Hashtables with Matlab

Related Question

MATLAB: Do I receive a “java.lang.OutOfMemoryError: Java heap space” error after upgrading to Database Toolbox 3.5.1 (R2009a)