Doubt about the code

#1

Plz explain line no 6 nd 7 . Why we need to create object of binary class using object of main class?

#2

Static fields and methods are connected to the class itself and not its instances. If you have a class A , a ‘normal’ method b , and a static method c , and you make an instance a of your class A , the calls to A.c() and a.b() are valid. Method c() has no idea which instance is connected, so it cannot use non-static fields.

The solution for you is that you either make your fields static or your methods non-static. You main could look like this then:

public class Main{
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		Main m = new Main();
		BinaryTree tree = new BinaryTree(sc);
		tree.leftView();

	}

	class BinaryTree {
            // can now access non-static fields
         }
}

or you could just say

public class Main{
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		//Main m = new Main();
		BinaryTree tree = new BinaryTree(sc);
		tree.leftView();

	}

	static class BinaryTree {
            ///code
        }
}