How does double dispatch work in Visitor pattern?

Question

I was looking into other questions related to the visitor pattern but couldn\'t understand the implementation of double dispatch in visitor pattern.

Please refer to

Answer 1

An example code, that shows double dispatch:

import java.util.Arrays;
import java.util.List;

class Client {
    public static void main(String[] args) {
        List nodes = Arrays.asList(new NodeA(), new NodeB());
        List visitors = Arrays.asList(new NodeVisitor1(), new NodeVisitor2());

        for (Node node : nodes) {
            for (NodeVisitor visitor : visitors) {
                node.accept(visitor);
            }
        }
    }
}

interface Node {
    void accept(NodeVisitor visitor);
}

interface NodeVisitor {
    void visit(Node node);
}

class NodeA implements Node {

    @Override
    public void accept(NodeVisitor visitor) {
        visitor.visit(this);
    }

    @Override
    public String toString() {
        return "Node A";
    }
}

class NodeB implements Node {

    @Override
    public void accept(NodeVisitor visitor) {
        visitor.visit(this);
    }

    @Override
    public String toString() {
        return "Node B";
    }
}

class NodeVisitor1 implements NodeVisitor {

    @Override
    public void visit(Node node) {
        System.out.println("Node visitor 1, node " + node);
    }
}

class NodeVisitor2 implements NodeVisitor {

    @Override
    public void visit(Node node) {
        System.out.println("Node visitor 2, node " + node);
    }
}

The output is:

Node visitor 1, node Node A
Node visitor 2, node Node A
Node visitor 1, node Node B
Node visitor 2, node Node B