How does double dispatch work in Visitor pattern?

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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 the link Visitor Pattern

How does double dispatch work in the Visitor pattern?

visitor-pattern double-dispatch design-patterns java
4 Answers

An example code, that shows double dispatch:

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

class Client {
    public static void main(String[] args) {
        List<Node> nodes = Arrays.asList(new NodeA(), new NodeB());
        List<NodeVisitor> 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
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