how to get the count of number of true values in Arraylist java

Question

hi I am new here and new in Java programming as well actually my problem is that I have a Array List of type Book in which I am storing Book name and title and set the OnLoan value explicitly by true or false but I am able to store true or false value for the Book arrayList but I want to count number of true value in my arrayList say if 3 books having borrowed status true I want the count as 3 I dont know how to get that count out from ArrayList in java please help me out here is my sample code I am getting the true value by calling the getOnLoanStatus() from book class which holds true and false values

int borrowCount=0;
     Book loanStatus = new Book();
     boolean l = loanStatus.getOnLoanStatus();
     //boolean to String conversion

     System.out.println("value of l is" + l);
     if(this.booksHeld.isEmpty()) 
      {
        return null;
      }
       for(int i=0;i<this.booksHeld.size();i++)
       {
         if(booksHeld.contains(l)) // compare the isbn string with getIsbn Method
         {
             borrowCount++;
         }
       }
        if(borrowCount==0) 
        {
            return "Libray: " + numberOfBooks() + "books " +  " 0 book on Loan";
        }
        else
        {
          return "Libray: " + numberOfBooks() + "books " + borrowCount + "on Loan";
        }

Can you clean the example up and make it complete? There are variables like booksHeld which I can assume is a List<Book>, and then you have comments that say "compare the isbn string with getIsbn Method", but there is no getIsbn method shown. — wkl
– wkl, Commented Mar 28, 2012 at 14:08
I am really sorry about that ignore that comments and yes books Held is my ArrayList object holding books for Library and user class and I am currently working on Library class ignore get isbn as well sorry for the inconvenience — Hardy
– Hardy, Commented Mar 28, 2012 at 14:16

amit · Accepted Answer · 2012-03-28 14:07:11Z

10

You can use a for-each loop, and check for each element if it is borrowed [assuming Book has a method onLoanStatus() which indicate if it is on load or not]

Should look something like that:

int count = 0;
for (Book b : booksHeld) { 
  if (b.getOnLoanStatus()) count++;
}
//now count holds the number of loaned books.

answered Mar 28, 2012 at 14:07

amit

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geisterfurz007 · Accepted Answer · 2019-11-04 09:23:46Z

10

As this question does not yet have the obligatory stream answer for Java 8:

long count = booksHeld.stream().filter(book -> book.getOnLoanStatus()).count();

Source with minor edits.

Straight forward approach: take the stream, filter it by predicate that must match boolean value true and count the matches in the stream for the filter.

edited Nov 4, 2019 at 9:23

answered Aug 2, 2017 at 6:14

geisterfurz007

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