Count the number of items in my array list

Question

I want to count the number of itemids in my array  can i get an example of how i would go about adding this to my code  code below   if  value    null  amp  amp   value isEmpty          Set set   value keySet        Object   key   set toArray        Arrays sort key        for  int i   0  i  lt  key length  i              ArrayList list    ArrayList  value get  String  key i             if  list    null  amp  amp   list isEmpty                  Iterator iter   list iterator                double itemValue   0              String itemId                    while  iter hasNext                      Propertyunbuf p    Propertyunbuf  iter next                    if  p    null                        itemValue   itemValue   p getItemValue   doubleValue                        itemId   p getItemId                                       buf2 append NL                   buf2 append                        itemId                               double amount   itemValue              totalAmount    amount

User · Answer

The only thing I would add to Mark Peters solution is that you don t need to iterate over the ArrayList - you should be able to use the addAll Collection  method on the Set   You only need to iterate over the entire list to do the summations

User · Answer

The number of itemIds in your list will be the same as the number of elements in your list   int itemCount   list size      However  if you re looking to count the number of unique itemIds  per  pst  then you should use a set to keep track of them   Set lt String gt  itemIds   new HashSet lt String gt            itemId   p getItemId    itemIds add itemId          later     int uniqueItemIdCount   itemIds size

User · Answer

Using Java 8 stream API     String   keys   new String 0       A map for keys and their count Map lt String  Long gt  keyCountMap   Arrays stream keys   collect Collectors groupingBy Function identity    Collectors counting      int uniqueItemIdCount  keyCountMap size

User · Answer

You want to count the number of itemids in your array  Simply use   int counter list size      Less code increases efficiency  Do not re-invent the wheel

User · Answer

Outside of your loop create an int   int numberOfItemIds   0  for  int i   0  i  lt  key length  i        Then in the loop  increment it   itemId   p getItemId    numberOfItemIds

User · Answer

You can get the number of elements in the list by calling list size    however some of the elements may be duplicates or null  if your list implementation allows null    If you want the number of unique items and your items implement equals and hashCode correctly you can put them all in a set and call size on that  like this   new HashSet lt  gt  list  size     If you want the number of items with a distinct itemId you can do this   list stream   map i - gt  i itemId  distinct   count     Assuming that the type of itemId correctly implements equals and hashCode  which String in the question does  unless you want to do something like ignore case  in which case you could do map i - gt  i itemId toLowerCase       You may need to handle null elements by either filtering them before the call to map  filter Objects  nonNull  or by providing a default itemId for them in the map call  map i - gt  i    null   null   i itemId

[java] Count the number of items in my array list

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