“Using java.lang.reflect
“ will answer all your questions. First fetch the Class
object using Class.forName()
, and then:
If I want to instantiate a class that I retrieved with
forName()
, I have to first ask it for ajava.lang.reflect.Constructor
object representing the constructor I want, and then ask thatConstructor
to make a new object. The methodgetConstructor(Class[] parameterTypes)
inClass
will retrieve aConstructor
; I can then use thatConstructor
by calling its methodnewInstance(Object[] parameters)
:Class myClass = Class.forName("MyClass"); Class[] types = {Double.TYPE, this.getClass()}; Constructor constructor = myClass.getConstructor(types); Object[] parameters = {new Double(0), this}; Object instanceOfMyClass = constructor.newInstance(parameters);
There is a newInstance()
method on Class
that might seem to do what you want. Do not use it. It silently converts checked exceptions to unchecked exceptions.
Note that this method propagates any exception thrown by the nullary constructor, including a checked exception. Use of this method effectively bypasses the compile-time exception checking that would otherwise be performed by the compiler. The
Constructor.newInstance
method avoids this problem by wrapping any exception thrown by the constructor in a (checked)InvocationTargetException
.