How to declare array of Unknown Length for below code

[sandeep43]

Hi Guys,

String [] DependentView = new String[1000];
String [] ParentView = new String[1000];

This is what i have declared of length 1000, but i want to store String of unknown length for same String statement i have passed, any idea?

Sandeep

[JosAH]

Yep, use a List<String> of some sort.

kind regards,

Jos

[Norm]

i want to store String of unknown length

The length of one String object won't be any problem when assigning it to an element of an array.
The number of Strings that you want to put in the array would be restricted to the size of the array.

[stchman]

Since they are all Strings you could use an ArrayList to first store the Strings. Each time you invoke the .add method the ArrayList size increases by one element. When you're done filling the ArrayList, you can create your String array and size it from the ArrayList size() method.

Remember that each element in an ArrayList is an Object so you will need to convert each element to a String.

ex.

ArrayList list = new ArrayList();

for( int i = 0; i < 100; i++ )
    list.add( "stuff" );

String[] strArray = new String[ list.size() ];

for( int j = 0; j < strArray.length; j++ )
    strArray[ j ] = list.get( j ).toString();

For example sake I created an ArrayList and put 100 words in it. I dimensioned the String array to the size of the ArrayList. I then converted each element of the ArrayList to a String and deposited them into the String array.

Now this will work, there might be another more efficient way to do the same thing.

[Norm]

Remember that each element in an ArrayList is an Object so you will need to convert each element to a String.

If you use Generics the compiler will take care of the conversion/casting for you.

there might be another more efficient way to do the same thing.

The ArrayList class has a method that will create and fill an array for you.

[stchman]

If you use Generics the compiler will take care of the conversion/casting for you.


The ArrayList class has a method that will create and fill an array for you.

I looked at the ArrayList in the API and the toArray() method returns Object[]. Would the OP not then have to create an array of Strings anyway since Object and String are not the same type?

[Norm]

The toArray method is overloaded. Look at the next one, it will return a String array.

public <T> T[] toArray(T[] a)

[stchman]

Ok, after some reading:

ArrayList<String> list = new ArrayList<String>();

for( int i = 0; i < 100; i++ )
    list.add( "stuff" );
        
String[] strArray = list.toArray( new String[ list.size() ] );

[sandeep43]

Hey later how can i flush values When i am using String[]

Sandeep

[sandeep43]

Actually the problem in for the first loop i have 4 values in my array, later for second loop i have 2 values. So when executing second time my String[] has 3rd and 4th values what that array had during first loop, so how to flush them out or clear them

Sandeep

[Norm]

What do you mean by "flush"?
Do you want to remove them from the array?
One way would be to set them to null. Then your logic would need to handle the case of the array having null entries.
Another way is to create a new array with a reduced size and copy the elements you want to keep from the old array to the new array.
These are reasons for you to consider using an ArrayList. The ArrayList class has methods to remove elements.