Convert ArrayList to String array in Android

Question

I have a ArrayList that contains values in the form [ann,john]. I want to convert this ArrayList into a String array in the form {"ann","john"}.

How should I do this?

My Android code:

     final Button markabsent = (Button) findViewById(R.id.Button02);
      markabsent.setOnClickListener(new View.OnClickListener() {
          public void onClick(View v) {

            // Perform action on click
             Toast.makeText(display.this,"You have marked the students absent",Toast.LENGTH_SHORT).show();

             SparseBooleanArray checkedabsent = lView.getCheckedItemPositions();



            for (int i = 0; i < arr2.length; i++) 
            {
                if (checkedabsent.get(i)) 
                {
                    items2.add(arr2[i]);
                    System.out.println(items2);

                }
            }

            Log.d("", "items:");
            for (String string : items2)
            {
                Log.d("string is", string);


            }  
          }
      });

My Logcat:

     11-10 21:44:00.414: INFO/System.out(2316): [ann, john, ann]
     11-10 21:44:00.414: DEBUG/(2316): items:
     11-10 21:44:00.414: DEBUG/string is(2316): ann
     11-10 21:44:00.414: DEBUG/string is(2316): john

I tried doing everything mentioned in the answers but my logcat just doesn't seem to imrove

Here is the one giving exceptions:

          11-10 22:14:20.855: INFO/System.out(3322): [Ljava.lang.String;@44eb6ff0
          11-10 22:16:38.186: ERROR/AndroidRuntime(3411): FATAL EXCEPTION: main
          11-10 22:16:38.186: ERROR/AndroidRuntime(3411): java.lang.ClassCastException: [Ljava.lang.Object;
          11-10 22:16:38.186: ERROR/AndroidRuntime(3411):     at com.example.display$2.onClick(display.java:124)
          11-10 22:16:38.186: ERROR/AndroidRuntime(3411):     at android.view.View.performClick(View.java:2408)
          11-10 22:16:38.186: ERROR/AndroidRuntime(3411):     at android.view.View$PerformClick.run(View.java:8816)
          11-10 22:16:38.186: ERROR/AndroidRuntime(3411):     at android.os.Handler.handleCallback(Handler.java:587)

Here is one more:

          11-10 22:14:20.875: DEBUG/string is(3322): ann
          11-10 22:14:20.875: INFO/System.out(3322): [Ljava.lang.String;@44eb7720
          11-10 22:14:20.875: INFO/System.out(3322): [Ljava.lang.String;@44eb7720
          11-10 22:14:20.885: INFO/System.out(3322): [Ljava.lang.String;@44eb7720
          11-10 22:14:20.895: DEBUG/string is(3322): john
          11-10 22:14:20.895: INFO/System.out(3322): [Ljava.lang.String;@44eb7de8
          11-10 22:16:38.186: ERROR/AndroidRuntime(3411):     at com.example.display$2.onClick(display.java:124)

possible duplicate of Convert ArrayList containing Strings to an array of Strings in Java? — Sruit A.Suk
– Sruit A.Suk, Commented Aug 5, 2015 at 7:41

DallaRosa · Accepted Answer · 2015-05-31 16:16:36Z

112

Use the method "toArray()"

ArrayList<String>  mStringList= new ArrayList<String>();
mStringList.add("ann");
mStringList.add("john");
Object[] mStringArray = mStringList.toArray();

for(int i = 0; i < mStringArray.length ; i++){
    Log.d("string is",(String)mStringArray[i]);
}

or you can do it like this: (mentioned in other answers)

ArrayList<String>  mStringList= new ArrayList<String>();
mStringList.add("ann");
mStringList.add("john");
String[] mStringArray = new String[mStringList.size()];
mStringArray = mStringList.toArray(mStringArray);

for(int i = 0; i < mStringArray.length ; i++){
    Log.d("string is",(String)mStringArray[i]);
}

http://developer.android.com/reference/java/util/ArrayList.html#toArray()

edited May 31, 2015 at 16:16

answered Nov 10, 2011 at 16:25

DallaRosa

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3 Comments

JimmyB Over a year ago

Same problem here as in Casey's original post: toArray() returns an Object[] which cannot be cast to String[]. Mind to edit your answer?

DallaRosa Over a year ago

Sure, just got it fixed and added the second alternative of first creating the Array and then passing it as a parameter to the toArray() method

Moxet Khan Over a year ago

Please add a closing ) in Log.d("string is",(mStringArray[i]);

Bobby · Accepted Answer · 2011-11-10 17:00:49Z

35

Well in general:

List<String> names = new ArrayList<String>();
names.add("john");
names.add("ann");

String[] namesArr = new String[names.size()];
for (int i = 0; i < names.size(); i++) {
    namesArr[i] = names.get(i);  
}

Or better yet, using built in:

List<String> names = new ArrayList<String>();
String[] namesArr = names.toArray(new String[names.size()]);

edited Nov 10, 2011 at 17:00

Bobby

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answered Nov 10, 2011 at 16:23

user147373

3 Comments

Parth Doshi Over a year ago

In ur 1st way if I do a println of SOPln(namesArr) .. I get this : pastie.org/2842530

user147373 Over a year ago

for the second issue, you will need to loop over the array to print the values.

Denys Kniazhev-Support Ukraine Over a year ago

There's no need to use new String[names.size()], new String[0] should work too.

Mihai Popescu · Accepted Answer · 2011-11-10 20:36:20Z

10

String[] array = new String[items2.size()];
items2.toArray(array);

edited Nov 10, 2011 at 20:36

user147373

answered Nov 10, 2011 at 16:28

Mihai Popescu

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3 Comments

Parth Doshi Over a year ago

if I use this I get something like this in logcat on SOP of array: pastie.org/2842530 . Why dont I get "john","ann" in "array"?

JimmyB Over a year ago

That's because an array converted to a String will look just like that. If you want to System.out.println() the array's elements you will have to implement this yourself - unlike for ArrayList which already has its own implementation of toString().

Parth Doshi Over a year ago

so then how do I implement that ? How can I know the contents of the String "array" ..Is there any other way?

Abdul.Moqueet · Accepted Answer · 2017-02-04 20:04:55Z

6

I know im very late to answer this. But it will help others, I was also stucked on this.

Here is what i did to get it work.

String[] namesArr = (String[]) names.toArray(new String[names.size()]);

edited Feb 4, 2017 at 20:04

answered Feb 4, 2017 at 19:53

Abdul.Moqueet

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Comments

Ishan Fernando · Accepted Answer · 2018-02-06 11:24:08Z

3

You can try this code

String[] stringA = new String[stringArrayList.size()];
stringArrayList.toArray(stringA)
System.out.println(stringA[0]);

answered Feb 6, 2018 at 11:24

Ishan Fernando

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Comments

Vishnu V S · Accepted Answer · 2015-04-22 11:18:27Z

2

try this

List<String> list = new ArrayList<String>();
list.add("List1");
list.add("List2");

String[] listArr = new String[list.size()];
listArr = list.toArray(listArr );

for(String s : listArr )
    System.out.println(s);

answered Apr 22, 2015 at 11:18

Vishnu V S

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Comments

Michael Banzon · Accepted Answer · 2011-11-10 16:23:38Z

1

You could make an array the same size as the ArrayList and then make an iterated for loop to index the items and insert them into the array.

answered Nov 10, 2011 at 16:23

Michael Banzon

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