How does this assignment operation work..?

I came across something new which i really found hard to understand.. Here is what i have done and it works perfectly fine..

    Vector<String[]> v = new Vector<String[]>();
    v.add(s);

    String[][] s1 = new String[v.size][]
    v.toArray(s1);

my question is how does it work even though method toArray() takes only 1-D array as argument..? I'm not muc开发者_高级运维h old for java programming so seeking an explanation..

Thanks in advance..

There are only really 1-D arrays in Java - where it looks like you've got a multi-dimensional array, it's actually just an array of arrays.

So if we ignore the fact that String[] itself is an array, and replace it with StringArray everywhere, we get this code:

Vector<StringArray> v = new Vector<StringArray>();
v.add(s);

StringArray[] s1 = new StringArray[v.size()];
v.toArray(s1);

Now that doesn't look so odd, right? s1 is an array of string arrays, and v is a vector of string arrays. v.toArray() takes an array of string arrays as a parameter, so we can use s1 as the argument.

It's simple: v is a vector of 1-D arrays, toArray returns a 1-D array of whatever elements in the vector are (in this case 1-D arrays). The result is a 1-D array of 1-D arrays, more commonly known as a 2-D array.

toArray() accepts a 1-D array of objects.

A string array is an object.

s1 is an array of string arrays.

QED

The argument is treating "String[][]" as a "1-dimensional array" of the "String[]" objects.

In this case, Vector.toArray(T[] a) takes an array of T's. Let's replace the generic T with the type "String[]" (note that a String[] is an object). So this means Vector.toArray(String[][] a) takes String[][] as an argument.