public class Test {
     public void disp(Object o) {
       System.out.println("Object Vesion");
     }
     public void disp(String s) {
       System.out.println("String Vesion");
     }
 public static void main(String args[]) {
        Test t=new Test();
        t.disp(null);
  }
}

the above compiles and displays String Vesion.how it is....explain....

public class Test {
     public void disp(StringBuffert sb {
       System.out.println("StringBuffer Vesion");
     }
     public void disp(String s) {
       System.out.println("String Vesion");
     }
 public static void main(String args[]) {
        Test t=new Test();
        t.disp(null);
  }
}

the aboce code generates comile time error
Test.java:10: reference to disp is ambiguous, both method
disp(java.lang.StringB
uffer) in Test and method disp(java.lang.String) in Test match
        t.disp(null);
         ^

why explain .........