How to use the same Scanner across multiple classes in Java

Question

I have a program that uses multiple classes, I want the other classes to be able to access the same scanner that I have declared in the main class, I assume it would be done using some sort of get method, however I am unable to find any resources to help me.

Here are the Scanners that I have made in my main class:

  Scanner in = new Scanner(System.in);
            System.out.println("Enter a filename");
            String filename = in.nextLine();
            File InputFile = new File (filename);
            Scanner reader = new Scanner(filename);

The reader Scanner is the one I want to be able to access across the other classes that make up the program, can anyone give me some guidance on how I can do this? Thanks a lot for any help!

Answer 1

Simply use public static final Scanner in = new Scanner(System.in); in you main class. After that you can call it from anywhere by MainClassName.in.

Also, be careful with arguments you pass to Scanner. I guess you wanted to put InputFile into Scanner, rather than filename =)

File InputFile = new File (filename);
Scanner reader = new Scanner(filename);

Answer 2

Answering your question about dependency injection: here's a rough idea of dependency injection (via constructor):

public void wire() {
    ...
    Scanner reader = new Scanner(filename);
    ClassA objectA = new ClassA(reader);
    ClassB objectB = new ClassB(reader);
    ...
}

class A (class B would have a similar constructor):

public class ClassA {

    private Scanner reader;

    public ClassA(Scanner reader) {
        this.reader = reader;
    }
    ...
}

So the idea is that you create and wire up your objects in wire() method.