Thread: Copying Arrays

Originally Posted by Junky

One thing you have to get clear is that copying an array does not automatically mean that you will have two unique arrays if objects are involved. Depending upon how you do it, both arrays probably refer to the same objects. Consider the following code:

import java.util.Arrays;
 
class Juju {
    private String value;
 
    Juju(String s) {
        value = s;
    }
 
    public String toString() {
        return value;
    }
 
    public void change(String s) {
        value = s;
    }
 
    public static void main(String[] args) {
        Juju[] one = {new Juju("one"), new Juju("two"), new Juju("three")};
        Juju[] two = Arrays.copyOf(one, one.length);
        one[0].change("ten");
        System.out.println(two[0]);
    }
}

Even though the code changes the value of the object in array one the output is "ten" because array two also refers to the same object.

Ok, I began typing my second array....when I reach.....""Array." once I type in the period, a small list of java methods come up. A LOT of copyOf comes up. Which one should I use?

Hmmm, when choosing a copyOf method, I chose the very first option...followed thru with code...and no matter what I seem to do....I get a squiggly line underneath my second parameter. Whether I choose, book.size, book.length(doesnt recognize lenght)....I get syntax error. Argh, I feel so close!!!

 ArrayList <PhoneBookEntry> book = new ArrayList <PhoneBookEntry>();          <-----my first arraylist
 ArrayList <PhoneBookEntry> copiedBook = new ArrayList <PhoneBookEntry>(); <------ the 2nd list in which I wish to copy the first
 copiedBook = Arrays.copyOf(book, book.size());    <-------------------------the squiggly line appears under the phrase book.size.

I do want to copy the contents of one ArrayList, into another. I guess I didn't see what I wrote.