title: instantiate an object and invoking a method via a .class file using reflection in JAVA?
body: <p>I have a .class file and know nothing about the .class file, including class name, fields or methods. What I need to do is finding out everything about the class and instantiate an object of the class. </p>
  
  <p>Remember that we know nothing about inside the .class file, after calling getDeclareMethod() ,getDeclareFields() and getDeclareConstructor(), I know that it contains a filed of String str and a void method with one String parameter which try to assign a name to the variable str and a pure constructor without any parameters.</p>
  
  <p>So the question is how to instantiate an object and invoke the method to assign a String to str? I know how to do it when the declarations of class or method are in the same file, but this one is an unknown .class file, I turn to you guys for help.    </p>