string[] modification

[mark I thomas]

I have a hashMap. Its key is some string object, the value is a fixed size string array. Initially I need all the elements in the string[] be null or "" (empty string). Then I want to retrieve a value from a hashmap and modify that string array. Then I want to retrieve the modified string[] which is the value in the hashmap. Here is my code --

    

                                HashMap hm = new HashMap();
		hm.put("a", new String[3]);
		hm.put("b", new String[3]);
		
		String[] a = (String[])hm.get("a");  // get one key's value
		a[2]="a2";  // modify it
		
		String[] aa = (String[])hm.get("a");  // retrieve one key's value
		for(int i=0; i<aa.length; i++){
			System.out.println("aa[" + i + "]=" + aa[i]);
		}

Question ---

1. String[] a = (String[])hm.get("a"); In this line I cast the retrieved object into string[] and assign it to a new string[] object "a", then I modify "a" array. Does it just modify the new array "a" or does it actually modify the array object that is stored as the value
for key "a" ? My output shows it works fine but I want to understand why.

2. code "new string[3]" automatically default the elements to null for this array. Is ther fast way to create a string array with "" (empty string) as default value ? The simple the better. How ?



>

[Christophe Verré]

1. The get method will return you the reference of the original array, so variable "a" is the same object as the one you created with "new String[3]".

2. You could use "new String[]{"","",""}". It's fine with only three elements, but it's not good with many more elements. One other way I can think of is by calling the Arrays#fill method.