type information - Using Class Literals

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If we reimplement PetCreator using lcass literals, the result is cleaner in many ways:

// typeinfo/pets/LiteralPetCreator.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Using class literals
// {java typeinfo.pets.LiteralPetCreator}
package typeinfo.pets;

import java.util.*;

public class LiteralPetCreator extends PetCreator {
  // No try block needed.
  @SuppressWarnings("unchecked")
  public static final List<Class<? extends Pet>> ALL_TYPES =
      Collections.unmodifiableList(
          Arrays.asList(
              Pet.class,
              Dog.class,
              Cat.class,
              Rodent.class,
              Mutt.class,
              Pug.class,
              EgyptianMau.class,
              Manx.class,
              Cymric.class,
              Rat.class,
              Mouse.class,
              Hamster.class));
  // Types for random creation:
  private static final List<Class<? extends Pet>> TYPES =
      ALL_TYPES.subList(ALL_TYPES.indexOf(Cat.class), ALL_TYPES.size());

  @Override
  public List<Class<? extends Pet>> types() {
    return TYPES;
  }

  public static void main(String[] args) {
    System.out.println(TYPES);
  }
}
/* Output:
[class typeinfo.pets.Cat, class typeinfo.pets.Rodent, class typeinfo.pets.Mutt, class typeinfo.pets.Pug, class typeinfo.pets.EgyptianMau, class typeinfo.pets.Manx
, class typeinfo.pets.Cymric, class typeinfo.pets.Rat, class typeinfo.pets.Mouse, class typeinfo.pets.Hamster]
*/

run it by in OnJava8-Examples directory:

% javac typeinfo/pets/LiteralPetCreator.java
% java typeinfo.pets.LiteralPetCreator

/**
     * Returns an unmodifiable view of the specified list.  This method allows
     * modules to provide users with "read-only" access to internal
     * lists.  Query operations on the returned list "read through" to the
     * specified list, and attempts to modify the returned list, whether
     * direct or via its iterator, result in an
     * <tt>UnsupportedOperationException</tt>.<p>
     *
     * The returned list will be serializable if the specified list
     * is serializable. Similarly, the returned list will implement
     * {@link RandomAccess} if the specified list does.
     *
     * @param  <T> the class of the objects in the list
     * @param  list the list for which an unmodifiable view is to be returned.
     * @return an unmodifiable view of the specified list.
     */
    public static <T> List<T> unmodifiableList(List<? extends T> list) {
        return (list instanceof RandomAccess ?
                new UnmodifiableRandomAccessList<>(list) :
                new UnmodifiableList<>(list));
    }

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refrences:

1. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/typeinfo/pets/LiteralPetCreator.java

2. http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/util/Collections.java

本文地址：https://blog.csdn.net/wangbingfengf98/article/details/112000393