println() : question from JQPlus

[geetha nagarajan]

What will happen when this code is compiled and run?

 
  public class Test
{
 public static void main(String s[])
{
  System.out.println(null+null);
  System.out.println(null+true);
  System.out.println(true+null);
}
}

Acc.to JQPlus,the answer is the code won't compile.
I tried the above code ,it compiles and runs printing : nullnull
nulltrue
truenull

 
public class Test1
{
 public static void main(String s1[])
{
System.out.println(null);
}
}

In this case,it gives a compiler error ,as it's an ambiguous reference : bcos println() can take both char[] & String as parameters.
Could someone clarify these 2 cases ?
Thanks in advance.

[Jessica Sant]

1st case:
I tried to compile it, but got the following compile-time errors:

C:\blah>javac NullTest.java
NullTest.java:5: Incompatible type for +. Can't convert null to int.
      System.out.println(null+null);
                             ^
NullTest.java:6: Incompatible type for +. Can't convert null to int.
      System.out.println(null+true);
                             ^
NullTest.java:6: Incompatible type for +. Can't convert boolean to int.
      System.out.println(null+true);
                             ^
NullTest.java:7: Incompatible type for +. Can't convert boolean to int.
      System.out.println(true+null);
                             ^
NullTest.java:7: Incompatible type for +. Can't convert null to int.
      System.out.println(true+null);
                             ^
5 errors

2nd case
Sorta self explanitory by the error message isn't it? if you change the code to this (and avoid the ambiguity) things compile/run fine:

public class NullTest2
{
   public static void main(String s1[])
   {
      System.out.println((String)null);
   }
}