Best way to convert an ArrayList to a string

Answer 1

Most Java projects often have apache-commons lang available. StringUtils.join() methods is very nice and has several flavors to meet almost every need.

public static java.lang.String join(java.util.Collection collection,
                                    char separator)


public static String join(Iterator iterator, String separator) {
    // handle null, zero and one elements before building a buffer 
    Object first = iterator.next();
    if (!iterator.hasNext()) {
        return ObjectUtils.toString(first);
    }
    // two or more elements 
    StringBuffer buf = 
        new StringBuffer(256); // Java default is 16, probably too small 
    if (first != null) {
        buf.append(first);
    }
    while (iterator.hasNext()) {
        if (separator != null) {
            buf.append(separator);
        }
        Object obj = iterator.next();
        if (obj != null) {
            buf.append(obj);
        }
    }
    return buf.toString();
}

Parameters:

collection - the Collection of values to join together, may be null

separator - the separator character to use

Returns: the joined String, null if null iterator input

Since: 2.3

Answer 2

It's an O(n) algorithm either way (unless you did some multi-threaded solution where you broke the list into multiple sublists, but I don't think that is what you are asking for).

Just use a StringBuilder as below:

StringBuilder sb = new StringBuilder();

for (Object obj : list) {
  sb.append(obj.toString());
  sb.append("\t");
}

String finalString = sb.toString();

The StringBuilder will be a lot faster than string concatenation because you won't be re-instantiating a String object on each concatenation.

Answer 3

May not be the best way, but elegant way.

Arrays.deepToString(Arrays.asList("Test", "Test2")

import java.util.Arrays;

    public class Test {
        public static void main(String[] args) {
            System.out.println(Arrays.deepToString(Arrays.asList("Test", "Test2").toArray()));
        }
    }

Output

[Test, Test2]

Answer 4

If you're using Eclipse Collections, you can use the makeString() method.

ArrayList<String> list = new ArrayList<String>();
list.add("one");
list.add("two");
list.add("three");

Assert.assertEquals(
    "one\ttwo\tthree",
    ArrayListAdapter.adapt(list).makeString("\t"));

If you can convert your ArrayList to a FastList, you can get rid of the adapter.

Assert.assertEquals(
    "one\ttwo\tthree",
    FastList.newListWith("one", "two", "three").makeString("\t"));

Note: I am a committer for Eclipse Collections.

Answer 5

I see quite a few examples which depend on additional resources, but it seems like this would be the simplest solution: (which is what I used in my own project) which is basically just converting from an ArrayList to an Array and then to a List.

    List<Account> accounts = new ArrayList<>();

   public String accountList() 
   {
      Account[] listingArray = accounts.toArray(new Account[accounts.size()]);
      String listingString = Arrays.toString(listingArray);
      return listingString;
   }

Answer 6

Changing List to a readable and meaningful String is really a common question that every one may encounter.

Case 1. If you have apache's StringUtils in your class path (as from rogerdpack and Ravi Wallau):

import org.apache.commons.lang3.StringUtils;
String str = StringUtils.join(myList);

Case 2 . If you only want to use ways from JDK(7):

import java.util.Arrays;
String str = Arrays.toString(myList.toArray()); 

Just never build wheels by yourself, dont use loop for this one-line task.