Casting an object array to a string array

at 2008-07-19 in Further reading by friebe (0 comments)

While testing the new EASC server and client implementations we're currently working on, we asked ourselves how to cast an object array to, for example, a string array.

The following is an array of objects consisting solely of strings:

  Object[] strings= new Object[] { "Hello", "World" };

The first thing we tried was to cast it via (String[])strings. This is legal sourcecode but will raise a java.lang.ClassCastException in Java, and a System.InvalidCastException in C#, both at runtime.

Java
The correct way to do this is to create a new string array and copy the elements:

  String[] list= new String[strings.length];
  System.arraycopy(strings, 0, list, 0, strings.length);

To do this reflectively, the java.lang.reflect.Array class can be used:

  Array.newInstance(String.class, strings.length);

Funny enough, the return type for Array.newInstance is Object (and not Object[]).

C#
The same goes for C#, except for slight differences in the method names:

  // Hard-coded
  String[] list= new String[strings.Length];
  strings.CopyTo(list, 0);
  
  // Reflective
  Array.CreateInstance(typeof(String), strings.Length);

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Casting an object array to a string array

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