如何在文本文件中写入数组的内容？

Question

I have an array which has objects of people in a football team. It holds information such as their first name, second name and address. When i use the code shown below the text file contains values like this: member@29086037

The code is shown below:

try
{
    PrintWriter pr = new PrintWriter ("memberDetails.txt");
    for (int i = 0; i < collection.length; i++)
    {
    pr.println(collection[i]); 
    }
    pr.close();
} catch (FileNotFoundException ex)
{
    System.out.println(ex.getMessage());
    System.out.println("in" + System.getProperty("user.dir"));
    System.exit(1);
}

What am I doing wrong?

Answer 1

When you see that malarky with the numbers and class name like that, it means you haven't overriden your toString() method, so it defaults to Object.toString() .

So, override the public String toString() method on your member class.

Answer 2

When you do pr.println(collection[i]); as you didn't override it, you print Object::toString which represents the object in this way by default:

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())

To print each field, use properties of the object, for example:

collection[i].getName(); 
collection[i].getAddress(); 

Other option, is to override toString() method of member .

Answer 3

You have to provide the path to the file correctly. I would suggest creating a file object and then pass it to Printwriter. This way you can also make sure if File exist before assigning it to printwriter.

Answer 4

As others have pointed out, assuming you have a class that models the players, you should provide a toString() implementation in the class. For example:

public class Player {
    private String firstName;
    private String lastName;
    private String address;
    ...
    @Override
    public String toString() {
        return String.format("Name: %s, %s. Address: %s", lastName, firstName, address);
    }
}

After that's been done, it becomes trivial to write the player information into a file. Using an utility library such as Google's Guava , the solution simplifies into a one-liner:

Files.write(Joiner.on(StandardSystemProperty.LINE_SEPARATOR.value())
                  .join(collection),
            new File("memberDetails.txt"),
            Charsets.UTF_8);