Java dynamic function calling

Question

I have a String array that contains names of method in the yyyyyy class

In the xxxxxx class I'm making a yyyyyy instance (say obj). Now I can call obj.function_name(), except I want to read function_name from the String array in a loop. Is this possible?

Answer 1

It's possible using reflection, although you should probably question your design somewhat if you need that sort of behavior. Class.getMethod takes a String for the method name and returns a Method object, which you can then call .invoke on to call the method

I can't figure out the markdown to link these inline, but these Javadoc pages should be helpful:

• http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Class.html#getMethod(java.lang.String, java.lang.Class[])
• http://java.sun.com/j2se/1.4.2/docs/api/java/lang/reflect/Method.html#invoke(java.lang.Object, java.lang.Object[])

Sample code (assuming the yyyyyy methods take one int argument, just to show argument passing):

yyyyyy obj = new yyyyyy();
String[] methodNames = {"foo", "bar", "baz"};
for(String methodName : methodNames) {
    Method method = Class.forName("yyyyyy").getMethod(methodName, new Class[] {int.class});
    method.invoke(obj, 4); // 4 is the argument to pass to the method
}

Answer 2

Yes, using reflection and dynamic method invocation you can do this. If you google "java dynamic method invocation" you'll get some interesting hits.

Here is a tutorial. This implements a kind of plotting language like you are describing.

Answer 3

You can, using reflection. It is done by calling Yyyy.class.getMethod("methodName").invoke(someArgs)

You'd have to handle a bunch of exceptions, and your method must be public. Note that java coding conventions prefer methodName to method_name.

Using reflection, however, should be a last resort. You should be using more object-oriented techniques.

If you constantly need similar features, perhaps you can look at some dynamic language running on the java platform, like groovy