How to copy/add an Array to a List of Arrays

Question

I'm new in the java, and I've been battling in copying a String array to an ArrayList but it does not store the values, instead stores the address of the array.

String[] newLine = { "name", "location", "price" };
List<String[]> outList = new ArrayList<String[]>();
outList.add(newLine);

for(String[] rows: outList)
{
    System.out.println(row);
}

I get printed

["name", "location", "price"]

If i change the value of newHeader it changes as well in the List.

newLine[0] = "NEW VALUE";
for(String[] rows : outList)
{
    System.out.println(row);
}

Output:

["NEW VALUE", "location", "price"];

How do I just add/copy the values of the Array to the ArrayList?

Maybe It isn't clear but I would like to have something like this at the end:

outList should contain *n* String Arrays e.g.      

["name", "location", "price"] 
["name2", "location2", "price2"]
["name3", "location3", "price3"]
["name4", "location4", "price4"]

see this post: stackoverflow.com/questions/12149314/…

guillaume girod-vitouchkina
– guillaume girod-vitouchkina

2015-12-01 17:54:26 +00:00
Commented Dec 1, 2015 at 17:54 — guillaume girod-vitouchkina
– guillaume girod-vitouchkina, Commented Dec 1, 2015 at 17:54

Woot4Moo · Accepted Answer · 2015-12-01 17:50:51Z

3

you can simply do this:

list.addAll(Arrays.asList(myArray));

answered Dec 1, 2015 at 17:50

Woot4Moo

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3 Comments

Clashsoft Over a year ago

He doesn't want to add the individual elements, but the array itself. -.-

Woot4Moo Over a year ago

@Clashsoft that doesn't seem to be what he is asking 'add/copy the values of the Array to the ArrayList'

Z.Mike Over a year ago

@Woot4Moo it does not work. It throws an error "type mismatch: cannot convert from List<String> to Collection < ? extends String []>".

Clashsoft · Accepted Answer · 2015-12-01 17:56:25Z

2

You can achieve this by storing a copy of the array rather than the array itself:

String[] newLine = { "name", "location", "price" }
String[] copy = newLine.clone();
outList.add(copy);

The clone() method will create a copy of the array that has the same elements and size, but is a different reference / address.

If you now change an element of the original array, the copy doesn't change.

newLine[0] = "NEW VALUE";
System.out.println(Arrays.toString(newLine)); // prints [NEW VALUE, location, price]
System.out.println(Arrays.toString(copy)); // prints [name, location, price]

answered Dec 1, 2015 at 17:56

Clashsoft

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2 Comments

Z.Mike Over a year ago

but then If I would want to populate my outputList with n Array values then I would have to create n clones?

Cybran Over a year ago

Correct - but there is no other way. If you do not copy/clone your array you run into the problems you stated in the question. But don't worry, it's a shallow copy: the actual strings are not copied, so the overhead is not too bad.

Z.Mike · Accepted Answer · 2015-12-01 18:47:01Z

0

I have figured out that I can do this:

String[] newLine = { "name", "location", "price" };

List<String[]> outList = new ArrayList<String[]>();

outList.add(new String []{newLine[0], newLine[1], newLine[2]});

Now if I will change the value of newLine it will not alter the outList. But I'm not sure if there is a better way to do this.

answered Dec 1, 2015 at 18:47

Z.Mike

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1 Comment

Paul Boddington Over a year ago

new String []{newLine[0], newLine[1], newLine[2]} is essentially the same as newLine.clone(). I think you should probably accept @Clashsoft's answer...

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