Using for loop to get all elements in an ArrayList?

GasMark6

Hi,

I'm trying to write a method that will use a for loop to iterate through all the positions in an ArrayList and add them to a String. I then want to return that String outside the for loop. Whenever I do this my for loop is ignored and what I initialised the String with is what is returned instead :S

[code]
String wordPos = null;
for (int i = 0; i < position.size() - 1; i++)
{
wordPos = wordPos + position.get(i);
}

return wordPos;
[/code]

I hope you can tell me what is going wrong or a better way of doing this.

Thanks

LozTaylor

Hey there.

First thing, you shouldn't initialise the String to a null. Instead of creating a blank String; which is what you want, it will create a String pointer pointing to a null object. If you do something like:

[code]String a = null;
Sysout.out.println(a);[/code]

You should see it output 'null'. Instead, you should do:

[code]String a = "";[/code]

The second problem is that your loop won't cover all of the elements in the ArrayList. You don't need the:

[code] i < position.size() - 1[/code]

The '-1' is unnecessary here. If the size of your ArrayList is 10, you want to go through all of the elements from 0 to 9.

Below is a working solution. I'm also making use of generics (the things in the '<>', as it's good practice, but you don't need to use them for this code to work).

[code]
import java.util.ArrayList;

public class MessClass {

public static void main (String[] args)
{
ArrayList myList = new ArrayList();

myList.add("First");
myList.add("Second");
myList.add("Third");
myList.add("Fourth");

MyClass mc = new MyClass();

System.out.println(mc.concatArrayList(myList) );
}

}


class MyClass
{

public String concatArrayList(ArrayList list)
{
String wordPos = "";

for (int i = 0; i < list.size(); i++)
{
wordPos = wordPos + list.get(i);
}

return wordPos;

}

}[/code]

Hope this helps!

LozTaylor

Hey there.

First thing, you shouldn't initialise the String to a null. Instead of creating a blank String; which is what you want, it will create a String pointer pointing to a null object. If you do something like:

[code]String a = null;
Sysout.out.println(a);[/code]

You should see it output 'null'. Instead, you should do:

[code]String a = "";[/code]

The second problem is that your loop won't cover all of the elements in the ArrayList. You don't need the:

[code] i < position.size() - 1[/code]

The '-1' is unnecessary here. If the size of your ArrayList is 10, you want to go through all of the elements from 0 to 9.

Below is a working solution. I'm also making use of generics (the things in the '<>', as it's good practice, but you don't need to use them for this code to work).

[code]
import java.util.ArrayList;

public class MessClass {

public static void main (String[] args)
{
ArrayList myList = new ArrayList();

myList.add("First");
myList.add("Second");
myList.add("Third");
myList.add("Fourth");

MyClass mc = new MyClass();

System.out.println(mc.concatArrayList(myList) );
}

}


class MyClass
{

public String concatArrayList(ArrayList list)
{
String wordPos = "";

for (int i = 0; i < list.size(); i++)
{
wordPos = wordPos + list.get(i);
}

return wordPos;

}

}[/code]

Hope this helps!

LozTaylor

Hey there.

First thing, you shouldn't initialise the String to a null. Instead of creating a blank String; which is what you want, it will create a String pointer pointing to a null object. If you do something like:

[code]String a = null;
Sysout.out.println(a);[/code]

You should see it output 'null'. Instead, you should do:

[code]String a = "";[/code]

The second problem is that your loop won't cover all of the elements in the ArrayList. You don't need the:

[code] i < position.size() - 1[/code]

The '-1' is unnecessary here. If the size of your ArrayList is 10, you want to go through all of the elements from 0 to 9.

Below is a working solution. I'm also making use of generics (the things in the '<>', as it's good practice, but you don't need to use them for this code to work).

[code]
import java.util.ArrayList;

public class MessClass {

public static void main (String[] args)
{
ArrayList myList = new ArrayList();

myList.add("First");
myList.add("Second");
myList.add("Third");
myList.add("Fourth");

MyClass mc = new MyClass();

System.out.println(mc.concatArrayList(myList) );
}

}


class MyClass
{

public String concatArrayList(ArrayList list)
{
String wordPos = "";

for (int i = 0; i < list.size(); i++)
{
wordPos = wordPos + list.get(i);
}

return wordPos;

}

}[/code]

Hope this helps!