No Exception while type casting with a null in java

You can cast null to any reference type without getting any exception.

The println method does not throw null pointer because it first checks whether the object is null or not. If null then it simply prints the string "null". Otherwise it will call the toString method of that object.

Adding more details: Internally print methods call String.valueOf(object) method on the input object. And in valueOf method, this check helps to avoid null pointer exception:

return (obj == null) ? "null" : obj.toString();

For rest of your confusion, calling any method on a null object should throw a null pointer exception, if not a special case.

You can cast null to any reference type. You can also call methods which handle a null as an argument, e.g. System.out.println(Object) does, but you cannot reference a null value and call a method on it.

BTW There is a tricky situation where it appears you can call static methods on null values.

Thread t = null;
t.yield(); // Calls static method Thread.yield() so this runs fine.

This is by design. You can cast null to any reference type. Otherwise you wouldn't be able to assign it to reference variables.

Casting null values is required for following construct where a method is overloaded and if null is passed to these overloaded methods then the compiler does not know how to clear up the ambiguity hence we need to typecast null in these cases:

class A {
  public void foo(Long l) {
    // do something with l
  }
  public void foo(String s) {
    // do something with s      
  }
}
new A().foo((String)null);
new A().foo((Long)null);

Otherwise you couldn't call the method you need.

Println(Object) uses String.valueOf()

public static String valueOf(Object obj) {
    return (obj == null) ? "null" : obj.toString();
}

Print(String) does null check.

public void print(String s) {
    if (s == null) {
        s = "null";
    }
    write(s);
}