How to convert object array to string array in Java

Question

I use the following code to convert an object array to a string array :

Object Object_Array[]=new Object[100];
// ... get values in the Object_Array

String String_Array[]=new String[Object_Array.length];

for (int i=0;i<String_Array.length;i++) String_Array[i]=Object_Array[i].toString();

But I wonder if there is another way to do this, something like :

String_Array=(String[])Object_Array;

But this would cause runtime error : Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;

What's the correct way to do it ?

Answer 1

A String[] is not an Object[], which is a little counter-intuitive. You're encountering the "Banana is-a fruit" but a "List Of Bananas is-not-a List Of Fruit" scenario.

You will have to extract and rebuild, as you're currently doing.

Answer 2

System.arraycopy is probably the most efficient way, but for aesthetics, I'd prefer:

 Arrays.asList(Object_Array).toArray(new String[Object_Array.length]);

Answer 3

The google collections framework offers quote a good transform method,so you can transform your Objects into Strings. The only downside is that it has to be from Iterable to Iterable but this is the way I would do it:

Iterable<Object> objects = ....... //Your chosen iterable here
Iterable<String> strings = com.google.common.collect.Iterables.transform(objects, new Function<Object, String>(){
        String apply(Object from){
             return from.toString();
        }
 });

This take you away from using arrays,but I think this would be my prefered way.

Answer 4

Another alternative to System.arraycopy:

String[] stringArray = Arrays.copyOf(objectArray, objectArray.length, String[].class);

Answer 5

If you want to get a String representation of the objects in your array, then yes, there is no other way to do it.

If you know your Object array contains Strings only, you may also do (instread of calling toString()):

for (int i=0;i<String_Array.length;i++) String_Array[i]= (String) Object_Array[i];

The only case when you could use the cast to String[] of the Object_Array would be if the array it references would actually be defined as String[] , e.g. this would work:

 Object[] o = new String[10];
 String[] s = (String[]) o;

Answer 6

This one is nice, but doesn't work as mmyers noticed, because of the square brackets:

Arrays.toString(objectArray).split(",")

This one is ugly but works:

Arrays.toString(objectArray).replaceFirst("^\\[", "").replaceFirst("\\]$", "").split(",")

If you use this code you must be sure that the strings returned by your objects' toString() don't contain commas.