What are the examples of Visitor design pattern in JDK?

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Pragya Keshap answered on February 10, 2023 Popularity 1/10 Helpfulness 1/10

answer What are the examples of Visitor design pattern in JDK?

What are the examples of Visitor design pattern in JDK?

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By using Visitor design pattern we can add new virtual methods to

existing classes without modifying their core structure.

In JDK there are many places where Visitor design pattern is used.

Some of these are as follows:

javax.lang.model.element.AnnotationValue and

AnnotationValueVisitor

java.nio.file.FileVisitor and SimpleFileVisitor

javax.lang.model.type.TypeMirror and TypeVisitor

javax.lang.model.element.Element and ElementVisitor

javax.faces.component.visit.VisitContext and

VisitCallbac

public class XMLExportVisitor implements Visitor {

    public String export(Shape... args) {
        StringBuilder sb = new StringBuilder();
        sb.append("<?xml version=\"1.0\" encoding=\"utf-8\"?>" + "\n");
        for (Shape shape : args) {
            sb.append(shape.accept(this)).append("\n");
        }
        return sb.toString();
    }

    public String visitDot(Dot d) {
        return "<dot>" + "\n" +
                "    <id>" + d.getId() + "</id>" + "\n" +
                "    <x>" + d.getX() + "</x>" + "\n" +
                "    <y>" + d.getY() + "</y>" + "\n" +
                "</dot>";
    }

    public String visitCircle(Circle c) {
        return "<circle>" + "\n" +
                "    <id>" + c.getId() + "</id>" + "\n" +
                "    <x>" + c.getX() + "</x>" + "\n" +
                "    <y>" + c.getY() + "</y>" + "\n" +
                "    <radius>" + c.getRadius() + "</radius>" + "\n" +
                "</circle>";
    }

    public String visitRectangle(Rectangle r) {
        return "<rectangle>" + "\n" +
                "    <id>" + r.getId() + "</id>" + "\n" +
                "    <x>" + r.getX() + "</x>" + "\n" +
                "    <y>" + r.getY() + "</y>" + "\n" +
                "    <width>" + r.getWidth() + "</width>" + "\n" +
                "    <height>" + r.getHeight() + "</height>" + "\n" +
                "</rectangle>";
    }

    public String visitCompoundGraphic(CompoundShape cg) {
        return "<compound_graphic>" + "\n" +
                "   <id>" + cg.getId() + "</id>" + "\n" +
                _visitCompoundGraphic(cg) +
                "</compound_graphic>";
    }

    private String _visitCompoundGraphic(CompoundShape cg) {
        StringBuilder sb = new StringBuilder();
        for (Shape shape : cg.children) {
            String obj = shape.accept(this);
            // Proper indentation for sub-objects.
            obj = "    " + obj.replace("\n", "\n    ") + "\n";
            sb.append(obj);
        }
        return sb.toString();
    }

}

https://refactoring.guru/design-patterns/visitor/java/example

Popularity 1/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: java

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Contributed on Feb 10 2023

Pragya Keshap

0 Answers Avg Quality 2/10

What are the examples of Visitor design pattern in JDK?

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