Thread: Copying Arrays

I am working with arrays and I am trying to figure out how to copy an array, using this website as help.http://download.oracle.com/javase/6/docs/api/java/util/Arrays.html#copyOf%28int[],%20int%29

I will paste my code below, but what I have so far is an array declared, named it "book", did some loops to get some user input and then display the outcome, and that works fine. I was told when you are copying an array, you create a new object and that's where I am stuck. I don't understand how to create and initialize this new object in order to copy my array. I hope I have the right idea at least lol.

import java.util.ArrayList;
import javax.swing.JOptionPane;
/* Exam Practice # 2
 * 10.20.2011
 * This file loads the array list with PhoneBookEntry objects, and displays the
 * content.
 */
public class PhoneBookDemo
{
 
    public static void main(String[] args)
    {   String name;
        String phoneNumber;
        String input;
        int inData;
        //Creates an array list that holds phonebookentrys, the name of it is called book
        ArrayList < PhoneBookEntry > book = new ArrayList < PhoneBookEntry > ();
 
        //bookPhone is my second object 
        PhoneBookEntry bookPhone;
        do//assure input is greater than 0
            {
            input = JOptionPane.showInputDialog("How many phone book listings to enter");
            inData = Integer.parseInt(input);
            }
        while(inData < 1);
        //load the array list
        for (int i = 0; i < inData; i++)
            {
            name = JOptionPane.showInputDialog(null,
            "Enter the name:", "Entry" + (i + 1) +
            JOptionPane.PLAIN_MESSAGE);
 
            phoneNumber = JOptionPane.showInputDialog(null,
            "Enter the phone number:", "Entry" + (i + 1) +
            JOptionPane.PLAIN_MESSAGE);
 
            //Primary phonebook object (named it book)
            book.add(new PhoneBookEntry(name, phoneNumber));
 
            }
       //Create a loop that gets objects from the other class file and maybe switch them around
       System.out.println("Name"  + "\tPhone Number" );
       for (int i = 0; i < book.size(); i++)
            {
 
             System.out.println(book.get(i).getName() + "\t" + book.get(i).getPhoneNumber());
            }
 
 
            //Secondary phonebook object for switching
            //Use methods from the Array list to switch, or replace
            //Print out a paper for each one so you know they all work
            //Refer to Page 433 for "Copying Arrays"
            //http://download.oracle.com/javase/6/docs/api/java/util/ArrayList.html
            //http://download.oracle.com/javase/6/docs/api/java/util/Arrays.html
              bookPhone.add(new PhoneBookEntry(name, phoneNumber));
 
 
 
//**********************Secondary phonebook object****************************\\ 
 
        //PhoneBookEntry bookPhone;
        /*do//assure input is greater than 0
            {
            input = JOptionPane.showInputDialog("How many phone book listings to enter");
            inData = Integer.parseInt(input);
            }
        while(inData < 1);
        //load the array list
        for (int i = 0; i < inData; i++)
            {
            name = JOptionPane.showInputDialog(null,
            "Enter the name:", "Entry" + (i + 1) +
            JOptionPane.PLAIN_MESSAGE);
 
            phoneNumber = JOptionPane.showInputDialog(null,
            "Enter the phone number:", "Entry" + (i + 1) +
            JOptionPane.PLAIN_MESSAGE);
 
            //Secondary phonebook object (named it bookPhone)
            bookPhone.add(new PhoneBookEntry(name, phoneNumber));
            }
       //Create a loop that gets objects from the other class file and maybe switch them around
       System.out.println("Name"  + "\tPhone Number" );
       for (int i = 0; i < book.size(); i++)
            {
 
             System.out.println(book.get(i).getName() + "\t" + book.get(i).getPhoneNumber());
            }*/
 
    }
 
}

I read through your code and I can't find where you're trying to copy an array. Also, the page you linked to is for Arrays, and you're program is using ArrayList, which is a different class.

However, if I'm understanding your problem correctly, you'd copy an array with something like:
PhoneBookEntry[] copiedBook = Array.copyOf(book, book.length);

That first part, before the equals sign, is all that's meant by creating a new object. copyOf() returns an array, a NEW array, so you have to have a name to put it in, such as "copiedBook". As a general hint for using those method summary pages, always look at the far left column - it tells you what the method is going to return.

That's for copying an ARRAY to an ARRAY, and what you have is an ArrayList, which might not work. So, now you have to work out how to turn an ArrayList into an Array. You might look here: ArrayList (Java 2 Platform SE v1.4.2)

Hmmm, I understand that more lol. I am only two months in, but I get what your telling me. I tried implementing that into my code and following it through with a loop. I will copy my code below.

When I create a copy of an array, I need to run a loop after and display the info right? Otherwise...what's the point of copying something, and not showing it.

import java.lang.reflect.Array;
import java.util.ArrayList;
import javax.swing.JOptionPane;
/* Exam Practice # 2
 * This file loads the array list with PhoneBookEntry objects, and displays the
 * content.
 */
public class PhoneBookDemo
{
 
    public static void main(String[] args)
    {  String name;
        String phoneNumber;
        String input;
        int inData;
 
        //Creates an array list that holds phonebookentrys, the name of it is called book
        ArrayList < PhoneBookEntry > book = new ArrayList < PhoneBookEntry > ();
 
        do//assure input is greater than 0
            {
            input = JOptionPane.showInputDialog("How many phone book listings to enter");
            inData = Integer.parseInt(input);
            }
        while(inData < 1);
        //load the array list
        for (int i = 0; i < inData; i++)
            {
            name = JOptionPane.showInputDialog(null,
            "Enter the name:", "Entry" + (i + 1) +
            JOptionPane.PLAIN_MESSAGE);
 
            phoneNumber = JOptionPane.showInputDialog(null,
            "Enter the phone number:", "Entry" + (i + 1) +
            JOptionPane.PLAIN_MESSAGE);
 
            //Primary phonebook object (named it book)
            book.add(new PhoneBookEntry(name, phoneNumber));
 
            }
       //Create a loop that gets objects from the other class file and maybe switch them around
       System.out.println("Name"  + "\tPhone Number" );
       for (int i = 0; i < book.size(); i++)
            {
 
             System.out.println(book.get(i).getName() + "\t" + book.get(i).getPhoneNumber());
            }
 
            //Copy of the primary object    This what you told me I needed, I just substitued a few words, and followed with a loop. I still get syntax errors though. :(
            PhoneBookEntry[] copiedBook = Array.copyOf(book, book.length);
 
             System.out.println("Name"  + "\tPhone Number" );
       for (int i = 0; i < copiedBook.size(); i++)
            {
 
             System.out.println(copiedBook.get(i).getName() + "\t" + copiedBook.get(i).getPhoneNumber());
            }
 
    }
 
}

 PhoneBookEntry[] copiedBook = Array.copyOf(book, book.length);

Well, you must look into ArrayList in detail. There is difference between arrays and arraylist.
You are trying to actually copy two arrays, not arraylists and your book is an arraylist.
Well, if you want to copy an arraylist into the other, you must use this;

First_ArrayList.addAll(Second_ArrayList);

I will recommend you to go through arraylist topic in detail.
Good luck

In my second for loop, the .size, and .get give me red squiggly lines. I just copied from my first for loop, but I substituted the array names. I then tried copying your provided code into mine to try it out and it was ALL red lol. Sorry if I am being difficult, but I am still earning. When I get errors, I don't know enough information to fix the problems lol.

Originally Posted by AnnexTrunks

In my second for loop, the .size, and .get give me red squiggly lines. I just copied from my first for loop, but I substituted the array names. I then tried copying your provided code into mine to try it out and it was ALL red lol. Sorry if I am being difficult, but I am still earning. When I get errors, I don't know enough information to fix the problems lol.

Sometimes difficult is frustrating, however you never learn unless you ask the question.

Ok lets go over some of the Array info

double[] d = new double[5]; //<-- you have to declare a [b]size[/b]
 
ArrayList<Double> d = new ArrayList<Double>(); //<---- here you dont have to declare a size but you call [b] d.length[/b]

also Double is a Object
double is a primitive.

to get the data from a Double you have to parse it double value = Double.parseDouble( Obj.class ) ;

double[] d needs a loop of some sort example for loop,

for(int i =0 ; i < d.getSize() ;i++){
System.out.println( " in my array my double is : " + d[i]; // notice the i is the counter in this array you have to have it...
}// end for loop
 
Iterator iter = d.iterator();// my netbeans is shut down i pretty sure this is right for ArrayList Class

here you can have different loops

while(iter.hasNext())
for each
for ( Double doub : iter.next())

the code i wrote before is just an example and was not intended for copy paste.

now all you really have to do is to make a loop and assign the data in the first ArrayList to the second one in a single loop as well as use a print statement before middle and after to see what your doing...

those println() are really helpful all the time. It gives you an idea what is happening.... I have so many println() in my code its hard to read but then again I also use the break and debug in netbeans to see values when i have a lot.

Originally Posted by AnnexTrunks

Why is this line giving me troubles? The red squiggly line is below the "copyOf". Netbeans says it does not seem to be recognized. I am having so much trouble with this lol. Java is hard.

PhoneBookEntry[] copiedBook = ArrayList.copyOf(book, copiedBook.length);

what is PhoneBookEntry[]
your trying to use primitives.... with out defining
look at what wiki says about primitives

If you scroll up in my original post, you will see an Array declared, and PhoneBookEntry is the other class file I am referencing to. That file in itself is complete and functional. So is the original array and all my loops. My editor and myself does not run into problems until I start trying to make a copy of the array.

I feel like I'm so close to this, but it's so frustrating. I can't stop messing with it either because tomorrow I go in for testing lol. A break is needed but I don't have time.

I just need to somehow make a copy of my first array, and display the information. What sucks is that the problem I am having is probably SO small to you guys, and I'm going to feel like a putz for not seeing how to fix it.

Originally Posted by AnnexTrunks

If you scroll up in my original post, you will see an Array declared, and PhoneBookEntry is the other class file I am referencing to.

problem one PhoneBookEntry is not a array its a Class
PhoneBookEntry can be implemented as ArrayList<PhoneBookEntry> book = new ArrayList<PhonebookEntry>();


now fix the logic from this and then we'll continue. I am staying online for this so feel special....

Originally Posted by william

problem one PhoneBookEntry is not a array its a Class
PhoneBookEntry can be implemented as ArrayList<PhoneBookEntry> book = new ArrayList<PhonebookEntry>();


now fix the logic from this and then we'll continue. I am staying online for this so feel special....

There is nothing wrong with that statement. It works fine with the while loop, and for loop. It's not until after all that, when I began coding my copying thingy, I start getting errors.

Originally Posted by Junky

William

The issue is that OP is trying to call the copyOf method in the ArrayList class when that method does not exist. It has nothing to do with a PhoneBookEntry array.

relax Junky answer his question then don't badger me.

Originally Posted by Junky

I already have and then you come along and confuse the matter by making incorrect and irrelevant posts.

what ever help away I am going for my Martini. I am off work and I really don't need you.

There is too many people suggesting too many things. Sorry guys but I am more confused now then ever.