essay29.txt

Java Essay Serials 1 - Java Basics - 29. How to create object using reflection？
A new object instance can be created with reflection. There are two reflective methods for creating instances of classes: constructor.newInstance() and Class.newInstance(). 

for example, we use Class.newInstance() to create a new instance:
    public static void main(String[] args) {
        Class<?> clz;
	try {
		clz = Class.forName("java.util.HashMap");
		HashMap hm = (HashMap)(clz.newInstance());
	} catch (Exception e) {
		e.printStackTrace();
	}
    }

Then let us take a look at creating instance with parameterized constructor:
public class ConstructorDemo {
	private ConstructorDemo(HashMap hm) {
	}
	public static void main(String[] args) {
		Map<String, String> maps = new HashMap<String, String>();
	    
		maps.put("A", "Alice");
		maps.put("B", "Bob");
	    
	        Constructor ctor;
		try {
			ctor = ConstructorDemo.class.getDeclaredConstructor(HashMap.class);
		        ConstructorDemo cd = (ConstructorDemo)ctor.newInstance(maps);
		} catch (Exception e) {
			e.printStackTrace();
		}		    
	}
}

Using constructor to create new instance is preferred because:
Class.newInstance() can only invoke the zero-argument constructor, while Constructor.newInstance() may invoke any constructor, regardless of the number of parameters.
Class.newInstance() requires that the constructor be visible; Constructor.newInstance() may invoke private constructors under certain circumstances.