Generics

gistfile1.java

    public static void main( String[] args ) throws Exception {
        Map<String,String> sm = new HashMap(3);
        //barf1( sm ); // compile-time error
        barf2( sm ); 
        barf3( sm ); 

        for ( String s : sm.keySet()) {
            System.out.println( "key: "+s+" "+s.getClass());
        }
    }

    public static void barf1( Map<Object,Object> obj ) {
        obj.put( 1, 1 );
    }
    public static void barf2( Map<?,?> obj ) {
    }
    public static void barf3( Map obj ) {
        obj.put( 3, 3 );
    }