CODEWITHSUNDEEP
javaarraylist
lola
lola

Reputation: 5789

Count occurrences of a given string in an ArrayList

I have a list of strings , I browse it and count number of "x" strings as below but the count doesn't print me the expected value:

ArrayList<Integer> list = new ArrayList<Integer>();

List<String> strings = table.getValue(); //this gives  ["y","z","d","x","x","d"]

int count = 0;
for (int i = 0; i < strings.size(); i++) {
    if ((strings.get(i) == "x")) {
        count++;
        list.add(count);
    }
}

System.out.println(list);

this gives [] it should be 2 as I have 2 occurrences of "x"

Upvotes: 5

Views: 19649

Answers (5)

JRL
JRL

Reputation: 77995

There already is an existing method for this:

Collections.frequency(collection, object);

In your case, use like this (replace all of your posted code with this):

System.out.println(java.util.Collections.frequency(table.getValue(), "x"));

Upvotes: 13

John B
John B

Reputation: 32949

Since you are looking for both the elements as well as the size, I would recommend Guava's Iterables.filter method

List<String> filtered = Lists.newArrayList(
                     Iterables.filter(myList, 
                                      Predicates.equalTo("x")));
int count = filtered.size();

But as everyone else has pointed out, the reason your code is not working is the ==

Upvotes: 0

aioobe
aioobe

Reputation: 420951

You should compare strings using equals instead of ==. I.e. change

if ((list.get(i) == "x"))
                 ^^

to

if ((list.get(i).equals("x")))
                 ^^^^^^

== compares references, while .equals compares actual content of strings.

Related questions:

Upvotes: 4

Vaandu
Vaandu

Reputation: 4935

For String you should use equals method.

int ct = 0;
for (String str : table.getValue()) {
    if ("x".equals(str)) { // "x".equals to avoid NullPoniterException
        count++;
    }
}
System.out.println(ct);

Upvotes: 0

Tobias
Tobias

Reputation: 9380

You need to use:

list.get(i).equals("x");

!= / == only checks the reference.

I don't knwo why you're using a ArrayList to count. You would probably something like that:

int count = 0;
for (String s : table.getValue()) {
    if (s.equals("x")) {
        count++;
    }
}
System.out.println( count );

Upvotes: 1

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