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?](http://stackoverflow.com/questions/4042434/convert-arraylist-containing-strings-to-an-array-of-strings-in-java) — Sruit A.Suk, Aug 05 '15 at 07:41

DallaRosa · Accepted Answer · 2015-05-31T16:16:36.157

111

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 '15 at 16:16

answered Nov 10 '11 at 16:25

DallaRosa

5,737
2
35
53

1

Same problem here as in Casey's original post: *toArray()* returns an *Object[]* which cannot be cast to *String[]*. Mind to edit your answer? – JimmyB Nov 10 '11 at 17:04
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 – DallaRosa Nov 13 '11 at 12:14
1

Please add a closing ) in Log.d("string is",(mStringArray[i]); – Moxet Khan May 28 '15 at 15:27

score 35 · Answer 2 · edited Nov 10 '11 at 17:00

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 '11 at 17:00

Bobby

11,419
5
44
69

answered Nov 10 '11 at 16:23

Casey

12,070
18
71
107

In ur 1st way if I do a println of SOPln(namesArr) .. I get this : http://pastie.org/2842530 – Parth Doshi Nov 10 '11 at 16:36
for the second issue, you will need to loop over the array to print the values. – Casey Nov 10 '11 at 20:35
3

There's no need to use `new String[names.size()]`, `new String[0]` should work too. – Denys Kniazhev-Support Ukraine Apr 17 '19 at 14:09

score 10 · Answer 3 · edited Nov 10 '11 at 20:36

10

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

edited Nov 10 '11 at 20:36

Casey

12,070
18
71
107

answered Nov 10 '11 at 16:28

Mihai Popescu

103
5

if I use this I get something like this in logcat on SOP of array: http://pastie.org/2842530 . Why dont I get "john","ann" in "array"? – Parth Doshi Nov 10 '11 at 16:40
1

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()*. – JimmyB Nov 10 '11 at 16:57
so then how do I implement that ? How can I know the contents of the String "array" ..Is there any other way? – Parth Doshi Nov 10 '11 at 17:21

Abdul.Moqueet · Answer 4 · 2017-02-04T20:04:55.927

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 04 '17 at 20:04

answered Feb 04 '17 at 19:53

Abdul.Moqueet

902
12
19

score 2 · Answer 5 · answered Apr 22 '15 at 11:18

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 '15 at 11:18

Vishnu V S

355
1
10

score 2 · Answer 6 · answered Feb 06 '18 at 11:24

2

You can try this code

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

answered Feb 06 '18 at 11:24

Ishan Fernando

2,758
1
31
38

score 1 · Answer 7 · answered Nov 10 '11 at 16:23

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 '11 at 16:23

Michael Banzon

4,879
1
26
28

Convert ArrayList to String array in Android

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