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  1. import java.util.*;
  2. import java.lang.*;
  3.  
  4. class Main
  5. {
  6.     public static void main (String[] args) throws java.lang.Exception
  7.     {
  8.         new Main().Run();
  9.     }
  10.  
  11.     public void Run()
  12.     {
  13.         Zoo zoo = new Zoo();
  14.         CountingVisitor v = new CountingVisitor();
  15.         zoo.Accept(v);
  16.         v.Summary();
  17.     }
  18.  
  19.     interface AnimalVisitor
  20.     {
  21.         void Visit(Giraffe giraffe);  // (1)
  22.         void Visit(Zebra zebra);      // (2)
  23.         void Visit(Lion lion);        // (3)
  24.         void Visit(Penguin penguin);  // (4)
  25.     }
  26.  
  27.     interface VisitableAnimal
  28.     {
  29.         void Accept(AnimalVisitor visitor);
  30.     }
  31.  
  32.     class Zoo
  33.     {
  34.         VisitableAnimal[] animals = new VisitableAnimal[]
  35.         {
  36.             new Giraffe(),
  37.             new Zebra(),
  38.             new Lion(),
  39.             new Penguin()
  40.         };
  41.  
  42.         public void Accept(AnimalVisitor visitor)
  43.         {
  44.             for (VisitableAnimal a : animals)
  45.                 a.Accept(visitor);
  46.         }
  47.     }
  48.  
  49.     class Giraffe implements VisitableAnimal
  50.     {
  51.         public void Accept(AnimalVisitor visitor)
  52.         {
  53.             visitor.Visit(this);  // calls (1)
  54.         }
  55.     }
  56.  
  57.     class Zebra implements VisitableAnimal
  58.     {
  59.         public void Accept(AnimalVisitor visitor)
  60.         {
  61.             visitor.Visit(this);  // calls (2)
  62.         }
  63.     }
  64.  
  65.     class Lion implements VisitableAnimal
  66.     {
  67.         public void Accept(AnimalVisitor visitor)
  68.         {
  69.             visitor.Visit(this);  // calls (3)
  70.         }
  71.     }
  72.  
  73.     class Penguin implements VisitableAnimal
  74.     {
  75.         public void Accept(AnimalVisitor visitor)
  76.         {
  77.             visitor.Visit(this);  // calls (4)
  78.         }
  79.     }
  80.  
  81.     class CountingVisitor implements AnimalVisitor
  82.     {
  83.         int numberOfMammals;
  84.         int numberOfBirds;
  85.         int numberOfMonochromeAnimals;
  86.         public void Summary()
  87.         {
  88.             System.out.printf("Discovered %d mammals, %d birds\n", numberOfMammals, numberOfBirds);
  89.             System.out.printf("Total %d monochrome animals\n", numberOfMonochromeAnimals);
  90.         }
  91.         public void Visit(Giraffe giraffe)
  92.         {
  93.             numberOfMammals++;
  94.         }
  95.         public void Visit(Zebra zebra)
  96.         {
  97.             numberOfMammals++;
  98.             numberOfMonochromeAnimals++;
  99.         }
  100.         public void Visit(Lion lion)
  101.         {
  102.             numberOfMammals++;
  103.             System.out.println("Lions are NOT scary");
  104.         }
  105.         public void Visit(Penguin penguin)
  106.         {
  107.             numberOfBirds++;
  108.             numberOfMonochromeAnimals++;
  109.         }
  110.     }
  111. }
Success #stdin #stdout 0.08s 381248KB
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Lions are NOT scary
Discovered 3 mammals, 1 birds
Total 2 monochrome animals
https://ideone.com/eTo9J1
language:
Java (12.0.1)
created:
10 years ago
visibility:
public

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