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20161008 Reflection

This is a small explanation for how to use reflection in Java like I do in my example for code of CISystem

This explanation shall not replace a documentation, it is by no means complete and I am no expert for this yet, but since I did not had much more when I started, I thought this might be interesting for you :

You ask with Class.forName() for the class object.

You have to pass the full qualified class name, including the full package structure.

This example shows it for a String :

Class<?> classType = Class.forName("java.lang.String");

With classType.getConstructor() you get the default constructor :

	Constructor<?> ctor = classType.getConstructor();

With the constructor and a type cast you create your object :

String s = (String)ctor.newInstance();

When you want to request a constructor which requires parameters, you provide a variable argument list when requesting the constructor with getConstructor(Class<?>... parameterTypes) and you pass a variable argument list containing these parameters calling newInstance(Object... initargs).

This example shows how to do it with creating a String :

		Class<?> clazz = Class.forName("java.lang.String");
		Constructor<?> ctor = clazz.getConstructor(String.class);
		String s = (String)ctor.newInstance(new Object[] { "Hello World!" });
		System.out.println(s);

which prints

  Hello World!