Question

When and why would somebody do the following:

doSomething( (MyClass) null ); 

Have you ever done this? Could you please share your experience?

Answer 1

If doSomething is overloaded, you need to cast the null explicitly to MyClass so the right overload is chosen:

public void doSomething(MyClass c) {     // ... }  public void doSomething(MyOtherClass c) {     // ... } 

A non-contrived situation where you need to cast is when you call a varargs function:

class Example {     static void test(String code, String... s) {         System.out.println('code: ' + code);         if(s == null) {             System.out.println('array is null');             return;         }         for(String str: s) {             if(str != null) {                 System.out.println(str);             } else {                 System.out.println('element is null');             }         }         System.out.println('---');     }      public static void main(String... args) {         /* the array will contain two elements */         test('numbers', 'one', 'two');         /* the array will contain zero elements */         test('nothing');         /* the array will be null in test */         test('null-array', (String[])null);          /* first argument of the array is null */         test('one-null-element', (String)null);          /* will produce a warning. passes a null array */         test('warning', null);     } } 

The last line will produce the following warning:

Example.java:26: warning: non-varargs call of varargs method with inexact argument type for last parameter;
cast to java.lang.String for a varargs call
cast to java.lang.String[] for a non-varargs call and to suppress this warning