Check a string is present in the ArrayList?

Question

I have a string. Now how to check that the string is present in my array list?

Suppose:

str="nokia"
mobiles[0]="samsung"
mobiles[1]="nokia"
mobiles[2]="blackberry"

I have tried

Boolean match=false;    
for(int j = 0 ; j <= 15 ; j++) {
   match =mobiles[j].compare(str);
   if(match == true) {
     break;
   }
}

But .compare(str) is showing error.

Surely you can be more specific than "showing error"? *What* error? — meriton, Dec 29 '13 at 13:11
Do .equals checks the string is present in the string array? — Anik_Datta, Dec 29 '13 at 13:14
The error is: The method compare(Phones) in the type Phones is not applicable for the arguments (String) — Anik_Datta, Dec 29 '13 at 13:16
That error is impossible. If `mobiles` is a `Phones[]`, then you can't put strings into it. — Marko Topolnik, Dec 29 '13 at 13:55

PakkuDon · Answer 1 · 2013-12-31T03:28:46.240

I'm guessing that compare(str) is throwing an error because there is no function named compare() for the String class.

You could use equals() or equalsIgnoreCase() for case-insensitive matching. There's also compareTo() and compareToIgnoreCase() which are closer to what you typed. Note that the compareTo methods return an int value.

You can read up on the method descriptions here.

Here's an example using equalsIgnoreCase().

boolean match = false;    
for (int j = 0; j < mobiles.length; j++)
{
    match = mobiles[j].equalsIgnoreCase(str);
    if (match)
    {
         break;
    }
}

I've changed the terminating condition on the loop to use the length of the mobiles array. That way you won't need to change a hard-coded value in the event that you change the length of the array. It may also make the intent of the loop a little clearer.

Also as pointed out by ZouZou, writing match == true isn't necessary since match is itself a boolean value. This case doesn't seem to require the use of a wrapper class either so you could just declare match as the primitive type boolean.

Note : `if(match == true)` could be simplified to `if(match)` — Alexis C., Dec 29 '13 at 13:31
Also prefer using primitive `boolean` instead of a `Boolean` object. — Alexis C., Dec 29 '13 at 13:40

Ofer Lando · Answer 2 · 2013-12-29T13:40:55.423

2

In the question you mentioned an ArrayList but your example shows an Array. If you really have an ArrayList, just use something like:

if(mobiles.contains(str))
{
    //code here
}

If you have an Array, you can use the same "contains" after converting to ArrayList, using something like:

if(Arrays.asList(mobiles).contains(str))
{
    //code here
}

edited Dec 29 '13 at 13:40

answered Dec 29 '13 at 13:14

Ofer Lando

814
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`Arrays.toString()` doesn't convert an array to an ArrayList. It does just return a String representation of the content of your array. You're probably looking for `Arrays.asList`. – Alexis C. Dec 29 '13 at 13:27
Thanks, ZouZou - you are obviously right - and I corrected my answer accordingly! – Ofer Lando Dec 29 '13 at 13:41

Magnus · Answer 3 · 2013-12-29T13:34:39.750

0

I suggest not using an operation for comparing the strings, but to do it directly:

boolean match = false;
for (j=0; j<=mobiles.length; j++) {
    if (mobiles[j].equals(str)) {
        match=true; break;
    }
}

If you don't need the match boolean later, you can delete that.

edited Dec 29 '13 at 13:34

answered Dec 29 '13 at 13:16

Magnus

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why would you use `==` to compare 2 string? – Novarg Dec 29 '13 at 13:20
Use `equals()`, to compare String values. – Alexis C. Dec 29 '13 at 13:20
1

If I were you, I'd either delete this answer or fix it, to avoid further down votes – Paul Samsotha Dec 29 '13 at 13:29
@Magnus See the link peeskillet posted in its comment. It explains why. – Alexis C. Dec 29 '13 at 13:37
Oh that seems quite logic. I fixed it. Thank you all! – Magnus Dec 29 '13 at 13:38
1

It does work with "==" as long as the strings are declared as constants like in the code snippet of the question asked. But it won't as soon as you use `new String("nokia")`. So it is best to use `equals()` because it will always work. – Ralf Dec 29 '13 at 13:39

Sitansu · Answer 4 · 2013-12-29T13:34:33.210

0

Try it:

 match =mobiles[j].equalsIgnoreCase(str);

equalsIgnoreCase compares this String to another String, ignoring case considerations. Two strings are considered equal ignoring case if they are of the same length, and corresponding characters in the two strings are equal ignoring case.

edited Dec 29 '13 at 13:34

answered Dec 29 '13 at 13:18

Sitansu

3,225
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score 0 · Answer 5 · answered Dec 29 '13 at 13:44

I would use Arrays's binarySearch(Object[] a, Object key) method in conjunction with its sort(Object[] a) method.

import java.util.Arrays; //put this at the top of your code

//your code here

String[] tempMobiles = mobiles; //temporary array that will be modified
Arrays.sort(tempMobiles); //sorts tempMobiles to prepare it for the next line
if(tempMobiles[Arrays.binarySearch(tempMobiles, str)].equals(str)) //if the string at the location returned by the binarySearch equals str...
{
    match = true; //sets match to true
}

Check a string is present in the ArrayList?

5 Answers5