reflection newinstance constructor java wrong number of arguments -

i learning reflection in java, , trying make example of constructor. there problem: "wrong number of arguments". searching through google , stackoverflow, cannot find same problem facing. can please me understand problem, thank much. codes:

    public static void main(string[] args) {     printclass f = new printclass();     class cl = f.getclass();     constructor<?> constructor[] = cl.getdeclaredconstructors(); // cl.getdeclaredconstructors() won't work...      f.field1 = 3;     printclass p1 = null;     printclass p2 = null;      try {         p1 = (printclass) constructor[0].newinstance(); // constructor[0].newinstance((object[])args) won't work...         p2 = (printclass) constructor[1].newinstance("this not printclass-------");          p1.print();         p2.print();      } catch (instantiationexception | illegalaccessexception             | illegalargumentexception | invocationtargetexception e) {         // todo auto-generated catch block         e.printstacktrace();     }      } }  class printclass { string s = "this printclass..."; int field1;  public printclass(string s) {     this.s = s; }  public printclass() { }  public void print() {     system.out.println(s); } 

}

and error

java.lang.illegalargumentexception: wrong number of arguments @ sun.reflect.nativeconstructoraccessorimpl.newinstance0(native method) @ sun.reflect.nativeconstructoraccessorimpl.newinstance(unknown source) @ sun.reflect.delegatingconstructoraccessorimpl.newinstance(unknown source) @ java.lang.reflect.constructor.newinstance(unknown source) @ reflection.mainclass.main(mainclass.java:18) 

again, thank helping me understand problem. :)

you're calling first of 2 constructors without argument. how can sure first constructor in array 1 without argument, , not 1 expecting string?

you can't, because the javadoc says:

the elements in array returned not sorted , not in particular order.

if want reference no-argument constructor of class, should call

cl.getdeclaredconstructor(); 

if want reference constructor taking string argument, should call

cl.getdeclaredconstructor(string.class);