Here is a sample code for creating an AMI from java code, using the Amazon's EC2 aws-java-sdk. I didn't manage to find a good "hello world" example for java, so I post my attempt here. I hope that you can kick-start working on the cloud.
First, you create an instance of the wrapper. Then, you can use it for example like:  createAMInstances(amiId, 1, 3, "mykey", "m1.small", "us-east-1a");