Convert a raw TwoTuple to TwoTuple<A,B> in a wrong way but didn't get any warning（Java Generics） -

enviroment： java se 7，eclipse 4.2 there r codes :

code 1:

import java.io.bytearrayoutputstream; public class tuple {     static twotuple<string, integer> f() {         return tuple("hi", 47);     }     static twotuple f2(){         return tuple(new bytearrayoutputstream(), 47);     }     public static <a,b> twotuple<a,b> tuple(a ,b b) {         return new twotuple<a, b>(a, b);     }     public static void main(string[] args) {         twotuple<string, integer> tt = f();         twotuple<boolean, integer> tt2 = f2(); //  there wrong          system.out.println(tt);         system.out.println(tt2);     } } 

code 2:

public class twotuple<a,b> {     private final a ;     private final b b ;     public twotuple(a f , b s) {         // todo auto-generated constructor stub         a= f;         b=s;     }     @override     public string tostring() {         // todo auto-generated method stub         return "a : " +a+ " ; b : "+b;     } } 

i made mistake ( twotuple tt2 = f2() )purposely,

but codes can run , compiler didn't think mistake，why?

your compiler accepts without errors (but not without warnings) since f2() method returning raw twotuple, , performing unchecked conversion twotuple<boolean, integer>.

if change f2() method type-safe signature below, error:

static twotuple<bytearrayoutputstream, integer> f2() {     return tuple(new bytearrayoutputstream(), 47); }