Java method returning List and a integer

Question

I have a method which reads a file and returns the contents of the text file in a list of String array. Find the implementation of the method and how I read it below. Now I want to have the number of lines in the file as well. I can get it as shown below in the comment - Can you please let me know how can I pass the integer variable as well from the method and read the integer as well?

Below - i.e read file should return List consisting of string arrays and an int as well.

public List<String[]> readFile() {
    final List<String[]> userList = new ArrayList<String[]>(); 
    BufferedReader bufferedreader = null;
    try {
        final String FileName="abs.txt"     
        bufferedreader = new BufferedReader(new FileReader(FileName));
        String line = null;
        while ((line = bufferedreader.readLine()) != null) {      
        // Add Variable ++ to get number of lines
            final String[] values = line.split(",");
            userList.add(values);   
        } 
    }
    catch (FileNotFoundException ex) {
        logError(ex.getMessage());
     }
    catch (IOException ex) {
        logError(ex.getMessage());
    }
    finally {
        try {
            if (bufferedreader != null){
                bufferedreader.close();
            }
         }
         catch (IOException ex) {
             logError(ex.getMessage());  
         }
     }
     return userList;
 }

This is how I read it:

 List<String[]> usersArray1 = new ArrayList<String[]>();
 usersArray1=complianceTracker.readFile();

Mark Elliot · Accepted Answer · 2011-07-11 02:24:38Z

3

In this instance, the number of lines in your file corresponds to the number of entries in usersArray1, you can get this as usersArray1.size().

answered Jul 11, 2011 at 2:24

Mark Elliot

77.4k23 gold badges147 silver badges162 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user684934 · Accepted Answer · 2011-07-11 02:23:33Z

1

Um, you can't. Java can only return 1 object.

You could make an encapsulating object to hold both the list and the int, or you can make the list you're using untyped and add in the int at the beginning or end, or just take the string value of the int and add it at the beginning or end and parse it later.

Edit: You know what? You're trying to get the int that holds the length of the list. You don't have to do this: lists already know how big they are, and you can retrieve it with size().

answered Jul 11, 2011 at 2:23

user684934

2 Comments

Mark Elliot Over a year ago

Re-read the problem, you don't need to carry the information somewhere else, the size of the List corresponds exactly to the number of lines in the file.

user684934 Over a year ago

@Mark got that as I was indenting the block =\

Ted Hopp · Accepted Answer · 2011-07-11 02:28:10Z

1

You can't return a list of String that also contains an integer. There are several things that can be done to work around this:

Redefine your method to take a List<String> argument; the method fills the list and returns an int.
In the calling code, just use the size() method of List to determine the number of entries after the method returns.
Define a class that contains an int and List<String> field, and return that instead of just the List<String>.
Pass an int[] array as an argument initialized to a single element. Store the integer return value in position 0 of the array. (Requires that the array be at least 1 long when the method is called.)

There are probably other techniques people can come up with.

answered Jul 11, 2011 at 2:28

Ted Hopp

235k48 gold badges413 silver badges533 bronze badges

Comments

Ajoy Bhatia · Accepted Answer · 2011-07-11 03:07:35Z

1

The simplest answer for this particular case is the one from Mark Elliott, who seems to be the only one who read what readFile() is doing. The number of lines returned is usersArray1.size().

Another minor point. (Repeating your usage example here for reference)

 List<String[]> usersArray1 = new ArrayList<String[]>();
 usersArray1=complianceTracker.readFile();

The first line is needlessly creating an instance of ArrayList<String[]> which will be ready to be GC'ed after the second line executes. The usersArray1 reference will then refer to the object created on the first line of the readFile() method, leaving no reference referring to the object created when usersArray1 was declared and initialized.

answered Jul 11, 2011 at 3:07

Ajoy Bhatia

6338 silver badges31 bronze badges

1 Comment

Ajoy Bhatia Over a year ago

All you need to do to invoke readFile() is: List<String[]> usersArray1 = complianceTracker.readFile();

Rudy · Accepted Answer · 2011-07-11 02:24:27Z

0

Create a bean.

public class ResultBean
{
   private List<String> userArray;
   private Integer anotherResult;
   //create get set here

}

later your readFile only need to return this resultBean class.

public ResultBean readFile()
{
 ResultBean bean = new ResultBean();
 //your existing logic here.
 bean.setUserArray(new ArrayList<String>()); //please implement your own set here. This is just an example.
 bean.setAnotherResult(Integer.valueOf(0));
 return bean;
}

answered Jul 11, 2011 at 2:24

Rudy

7,07212 gold badges53 silver badges87 bronze badges

1 Comment

Mark Elliot Over a year ago

Re-read the problem, you don't need to carry the information somewhere else, the size of the List corresponds exactly to the number of lines in the file.

Ed Staub · Accepted Answer · 2011-07-11 02:26:04Z

0

Whenever you need to return more than one piece of data, you have two choices, sometimes used together:

Use (write, if necessary) a class wrapping the data to be returned (in this case, a List and an integer).
Pass in as an argument that can hold some of the data, and can be modified by the method at hand.

answered Jul 11, 2011 at 2:26

Ed Staub

15.8k3 gold badges63 silver badges91 bronze badges

Comments

trutheality · Accepted Answer · 2011-07-11 02:27:44Z

0

There are basically two solutions to the problem of returning two things:

Create a class that keeps the two things together (makes a lot of sense if the integer and list of strings are passed around your code a lot).
Use various tricks for returning one (or both) through the parameters, including:
- Passing a variable that is a new int[1] to the function, then changing the contents of that "array" in the function and reading from it after the function.
- Passing in a class that encapsulates an integer in a mutable way (like an AtomicInteger).
- Passing the List object to the function and modifying it (while maintaining the same List reference).

answered Jul 11, 2011 at 2:27

trutheality

23.5k6 gold badges58 silver badges68 bronze badges

Comments

takrl · Accepted Answer · 2011-07-11 08:02:47Z

0

ints are passed by value and not reference by default in java. An easy way around this is to create a small class. Try something like

public class Data
{
    public List<String[]> usersArray1;
    public int value;
}

you could simply pass this to your method and store both the List of string[]s in there and the int could go in there too. Hope this helps!

edited Jul 11, 2011 at 8:02

takrl

6,5003 gold badges64 silver badges71 bronze badges

answered Jul 11, 2011 at 2:25

Satanfx55

931 gold badge3 silver badges7 bronze badges

Collectives™ on Stack Overflow

Java method returning List and a integer

8 Answers 8

Comments

2 Comments

Comments

1 Comment

1 Comment

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

Comments

2 Comments

Comments

1 Comment

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related