Question

I’m sure there is an extremely simple solution for this but I’m desperately struggling to find the answer. I’m trying to set the value from a main class into classA then retrieve that value in classB and do something else with it before returning the answer in the Main:

Example:

public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        ClassA classA = new ClassA();
        ClassB classB = new ClassB();

        System.out.println("Number: ");
        classA.setX(input.nextInt());

        System.out.println("Total: " + classB.printTotal());

    } // main
} // class

Class A:

public class ClassA {
    int x;

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }
} // class

ClassB:

public class ClassB {
    ClassA classA;

    public int printTotal() {
        int y = classA.getX() * 5;
        return y;
    }
} // class

Whatever I input returns null. I understand why this is the case but I don’t know the solution.

Answer 1

Your ClassB should define the dependency on ClassA either through constructor or a (setter) method:

public ClassB(ClassA classA) {
    this.classA = classA;
}

//or/and

public void setClassA(ClassA classA) {
    this.classA = classA;
}

And inject the dependency in main as follows:

ClassB classB = new ClassB(classA);