Something interesting about two overloaded constructors of FileInputStream in Java 7 API -

before talking fileinputstream, starting scenario there 2 valid, overloaded methods compiler confused , report compile-time error in response inputs.

here methods.

double calcaverage(double marks1, int marks2) {      return (marks1 + marks2)/2.0;   }    double calcaverage(int marks1, double marks2) {      return (marks1 + marks2)/2.0;   }  

here complete code showing use of methods:

class myclass {     double calcaverage(double marks1, int marks2) {               return (marks1 + marks2)/2.0;     }     double calcaverage(int marks1, double marks2) {              return (marks1 + marks2)/2.0;     }     public static void main(string args[]) {             myclass myclass = new myclass();             myclass.calcaverage(2, 3);     }   }   

because int literal value can passed variable of type double, both methods acceptable candidates literal values 2 , 3, , therefore compiler fails decide method pick.

this confused when take above concept me, dive further java 7 api fileinputstream class, , study 2 overloaded constructors of class.

1. public fileinputstream(string name) throws filenotfoundexception {.....}
2. public fileinputstream(file file) throws filenotfoundexception {.....}

according java 7 api source code, definition of version takes string object argument is:

public fileinputstream(string name) throws filenotfoundexception {          this(name != null ? new file(name) : null);   }  

now, if "name" indeed null, this(name != null ? new file(name) : null); evaluates this(null); in turn equivalent invocation of fileinputstream(null); both fileinputstream(string) , fileinputstream(file) become possible choices invoked null value. not give rise ambiguity? so, isn't there compile-time error that?

i understand filenotfoundexception raised, separate issue comes later. how ambiguity resolved before that?

your error here:

now, if "name" indeed null, this(name != null ? new file(name) : null); evaluates this(null); in turn equivalent invocation of fileinputstream(null);

it evaluates this((file) null) -- is, null value explicitly typed file. because expression name != null ? new file(name) : null has have type, , type specific type of 2 alternatives. in case, 1 alternative typed file , other typed null, specific common type file.

that's why it's able unambiguously resolve fileinputstream(file) constructor. it's analogous to:

file file = null; new fileinputstream(file);