Can't add element to ArrayList in for loop

Question

I am currently having the problem of not able to run the following code in Android app development.

import java.util.ArrayList;

public class Test extends FragmentActivity {

ArrayList<String> random;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
        for (int a=0; a<11; a++){
        random.add("a");
    }
            }
    }

I know the above code does useless action but that is simplified from my problem in the for loop code in JAVA. And I got this error from the error log, "unhandled event loop exception". Can anyone point out that what I am doing wrong please?

Don't make me mock you :) That's not a question for SO!

Ivan Nikolchov
– Ivan Nikolchov

2011-12-10 22:50:31 +00:00
Commented Dec 10, 2011 at 22:50 — Ivan Nikolchov
– Ivan Nikolchov, Commented Dec 10, 2011 at 22:50
@IvanNikolchov sorry. I am only a beginner.

JamesC
– JamesC

2011-12-11 00:26:01 +00:00
Commented Dec 11, 2011 at 0:26 — JamesC
– JamesC, Commented Dec 11, 2011 at 0:26

Jon Skeet · Accepted Answer · 2011-12-10 22:36:31Z

2

There are at least two problems (I suspect).

First, you're getting a NullPointerException because you're not initializing random with a value referring to an actual object.

Next, your syntax is bad here:

for (int a=0; a<11; a++);

Your code is only adding a single element to random - it's equivalent to:

for (int a=0; a<11; a++)
{
}
random.add("a");

I very much doubt that that's what you were intending. My guess is that you wanted this instead:

for (int a=0; a<11; a++)
{
    random.add("a");
}

answered Dec 10, 2011 at 22:36

Jon Skeet

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3 Comments

Justin Muller Over a year ago

Also, perhaps add an integer with random.add(a) was intended, and not adding a String with random.add("a")

Jon Skeet Over a year ago

@JustinMuller: Possibly (or rather, random.add(String.valueOf(a));. It's hard to tell, with no description about the intended behaviour...

JamesC Over a year ago

@JonSkeet Thanks, and the mistake was made when I edited the code on this website while I was trying to simplify the code.

Haoming Zhang · Accepted Answer · 2011-12-10 22:43:11Z

0

for (int a=0; a<11; a++) /*Delete the semicolon here*/
{
    random.add("a");
}

And also you need to initializing the ArrayList "random"。

answered Dec 10, 2011 at 22:43

Haoming Zhang

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