How to add String_Contains function programmatically via OES API

I've been working with OES API programmatically adding a policy. I've seen other's code being able to add attribute, value and operation (e.g. name as attribute, "James" as value and String_Equal as operation) to a condition rule in a policy.

What I want to achieve is being able to add "STRING_CONTAINS(value,attributeName)" function programmatically via OES API.

Here is code sample I was looking into.

ExtensionManager xMgr = app.getExtensionManager();

String functionName = "STRING_CONTAINS";

FunctionEntry methodEntry = xMgr.getFunction(functionName);

.....

I assume if I pass function name (operation name) to getFunction() method, methodEntry would recognize function such as String_Contains then I need to find a way to pass parameters (value and attributeName) but I am not sure how to do it.