119 lines
2.5 KiB
Java
119 lines
2.5 KiB
Java
// patterns/visitor/BeeAndFlowers.java
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// ©2015 MindView LLC: see Copyright.txt
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// Demonstration of "visitor" pattern.
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package patterns.visitor;
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import java.util.*;
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interface Visitor {
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void visit(Gladiolus g);
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void visit(Renuculus r);
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void visit(Chrysanthemum c);
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}
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// The Flower hierarchy cannot be changed:
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interface Flower {
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void accept(Visitor v);
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}
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class Gladiolus implements Flower {
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@Override
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public void accept(Visitor v) { v.visit(this);}
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}
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class Renuculus implements Flower {
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@Override
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public void accept(Visitor v) { v.visit(this);}
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}
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class Chrysanthemum implements Flower {
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@Override
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public void accept(Visitor v) { v.visit(this);}
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}
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// Add the ability to produce a string:
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class StringVal implements Visitor {
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String s;
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@Override
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public String toString() { return s; }
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@Override
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public void visit(Gladiolus g) {
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s = "Gladiolus";
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}
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@Override
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public void visit(Renuculus r) {
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s = "Renuculus";
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}
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@Override
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public void visit(Chrysanthemum c) {
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s = "Chrysanthemum";
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}
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}
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// Add the ability to do "Bee" activities:
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class Bee implements Visitor {
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@Override
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public void visit(Gladiolus g) {
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System.out.println("Bee and Gladiolus");
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}
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@Override
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public void visit(Renuculus r) {
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System.out.println("Bee and Renuculus");
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}
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@Override
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public void visit(Chrysanthemum c) {
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System.out.println("Bee and Chrysanthemum");
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}
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}
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class FlowerFactory {
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public static Flower newFlower() {
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switch((int)(Math.random() * 3)) {
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default:
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case 0: return new Gladiolus();
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case 1: return new Renuculus();
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case 2: return new Chrysanthemum();
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}
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}
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}
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public class BeeAndFlowers {
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public static void main(String args[]) {
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List<Flower> flowers = new ArrayList<>();
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for(int i = 0; i < 10; i++)
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flowers.add(FlowerFactory.newFlower());
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StringVal sval = new StringVal();
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Iterator<Flower> it = flowers.iterator();
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while(it.hasNext()) {
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it.next().accept(sval);
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System.out.println(sval);
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}
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// Perform "Bee" operation on all Flowers:
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Bee bee = new Bee();
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it = flowers.iterator();
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while(it.hasNext())
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it.next().accept(bee);
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}
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}
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/* Output:
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Gladiolus
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Chrysanthemum
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Chrysanthemum
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Renuculus
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Chrysanthemum
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Gladiolus
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Renuculus
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Renuculus
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Gladiolus
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Renuculus
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Bee and Gladiolus
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Bee and Chrysanthemum
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Bee and Chrysanthemum
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Bee and Renuculus
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Bee and Chrysanthemum
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Bee and Gladiolus
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Bee and Renuculus
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Bee and Renuculus
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Bee and Gladiolus
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Bee and Renuculus
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*/
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