116 lines
2.7 KiB
Java
116 lines
2.7 KiB
Java
// patterns/visitor/BeeAndFlowers.java
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// (c)2021 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Demonstration of the Visitor pattern.
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// {java patterns.visitor.BeeAndFlowers}
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package patterns.visitor;
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import java.util.*;
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import java.util.function.*;
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import java.util.stream.*;
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interface Visitor {
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void visit(Gladiolus g);
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void visit(Ranunculus 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 Ranunculus 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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private String s;
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@Override public String toString() { return s; }
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@Override public void visit(Gladiolus g) {
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s = "Gladiolus";
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}
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@Override public void visit(Ranunculus r) {
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s = "Ranunculus";
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}
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@Override 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 public void visit(Gladiolus g) {
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System.out.println("Bee and Gladiolus");
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}
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@Override public void visit(Ranunculus r) {
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System.out.println("Bee and Ranunculus");
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}
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@Override 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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static List<Supplier<Flower>> flowers =
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Arrays.asList(Gladiolus::new,
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Ranunculus::new, Chrysanthemum::new);
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static final int SZ = flowers.size();
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private static SplittableRandom rand =
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new SplittableRandom(47);
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public static Flower newFlower() {
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return flowers.get(rand.nextInt(SZ)).get();
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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 =
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Stream.generate(FlowerFactory::newFlower)
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.limit(10)
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.collect(Collectors.toList());
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StringVal sval = new StringVal();
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flowers.forEach(f -> {
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f.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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flowers.forEach(f -> f.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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Gladiolus
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Ranunculus
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Chrysanthemum
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Ranunculus
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Chrysanthemum
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Chrysanthemum
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Chrysanthemum
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Ranunculus
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Bee and Gladiolus
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Bee and Chrysanthemum
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Bee and Gladiolus
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Bee and Ranunculus
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Bee and Chrysanthemum
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Bee and Ranunculus
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Bee and Chrysanthemum
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Bee and Chrysanthemum
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Bee and Chrysanthemum
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Bee and Ranunculus
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*/
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