jmultimethod

DispatchTest.java (5506B)

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 // Copyright (c) 2009, 2015 Tomas Hlavaty All rights reserved.
 
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 
 // Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following
 // disclaimer. Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following
 // disclaimer in the documentation and/or other materials provided
 // with the distribution.
 
 // Neither the name of jmultimethod nor the names of its contributors
 // may be used to endorse or promote products derived from this
 // software without specific prior written permission.
 
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 // FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 // COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 // INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 // (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 // HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 // OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // FLAW: Java reasons about types of variables instead of values
 
 // for asteroid example see wikipedia visitor pattern
 
 package jmultimethod;
 
 public class DispatchTest {
     static class Asteroid {
         String id;
         public Asteroid(String id) {this.id = id;}
         public String id() {return id;}
     }
     static class Spaceship {
         String name;
         public Spaceship(String name) {this.name = name;}
         public String name() {return name;}
     }
     static class Static {
         static void colide(Asteroid x, Asteroid y) {
             System.out.println("AA colide " + x.id() + " with " + y.id());
         }
         static void colide(Asteroid x, Spaceship y) {
             System.out.println("AS colide " + x.id() + " with " + y.name());
         }
         static void colide(Spaceship x, Asteroid y) {
             System.out.println("SA colide " + x.name() + " with " + y.id());
         }
         static void colide(Spaceship x, Spaceship y) {
             System.out.println("SS colide " + x.name() + " with " + y.name());
         }
         static void colide(Object x, Object y) {
             System.out.println("OO colide " + x + " with " + y);
         }
         static void run() {
             run1();
             run2();
         }
         static void run1() {
             System.out.println("Static: explicitly typed");
             Asteroid a1 = new Asteroid("A1");
             Asteroid a2 = new Asteroid("A2");
             Spaceship s1 = new Spaceship("S1");
             Spaceship s2 = new Spaceship("S2");
             colide(a1, a2);
             colide(a1, s1);
             colide(s1, a1);
             colide(s1, s2);
         }
         static void run2() {
             System.out.println("Static: superclass typed");
             // here is the problem: the declared variable type is used
             // but it should be infered by the compiler instead
             Object a1 = new Asteroid("A1");
             Object a2 = new Asteroid("A2");
             Object s1 = new Spaceship("S1");
             Object s2 = new Spaceship("S2");
             colide(a1, a2);
             colide(a1, s1);
             colide(s1, a1);
             colide(s1, s2);
         }
     }
     static class Dynamic {
         void colide(Asteroid x, Asteroid y) {
             System.out.println("AA colide " + x.id() + " with " + y.id());
         }
         void colide(Asteroid x, Spaceship y) {
             System.out.println("AS colide " + x.id() + " with " + y.name());
         }
         void colide(Spaceship x, Asteroid y) {
             System.out.println("SA colide " + x.name() + " with " + y.id());
         }
         void colide(Spaceship x, Spaceship y) {
             System.out.println("SS colide " + x.name() + " with " + y.name());
         }
         void colide(Object x, Object y) {
             System.out.println("OO colide " + x + " with " + y);
         }
         void run() {
             run1();
             run2();
         }
         void run1() {
             System.out.println("Dynamic: explicitly typed");
             Asteroid a1 = new Asteroid("A1");
             Asteroid a2 = new Asteroid("A2");
             Spaceship s1 = new Spaceship("S1");
             Spaceship s2 = new Spaceship("S2");
             colide(a1, a2);
             colide(a1, s1);
             colide(s1, a1);
             colide(s1, s2);
         }
         void run2() {
             System.out.println("Dynamic: superclass typed");
             // here is the problem: dispatch is on the declared
             // variable type instead of the run-time value type
             Object a1 = new Asteroid("A1");
             Object a2 = new Asteroid("A2");
             Object s1 = new Spaceship("S1");
             Object s2 = new Spaceship("S2");
             colide(a1, a2);
             colide(a1, s1);
             colide(s1, a1);
             colide(s1, s2);
         }
     }
     public static void main(String args[]) {
         Static.run();
         new Dynamic().run();
     }
 }