about_java_interop.rb

require File.expand_path(File.dirname(__FILE__) + '/edgecase')

include Java

# Concepts
# * Pull in a java class
# * calling a method, Camel vs snake
# * Resolving module/class name conflicts
# * Showing what gets returned
# * Ruby Strings VS Java Strings
# * Calling custom java class
# * Calling Ruby from java???

class AboutJavaInterop < EdgeCase::Koan
 def test_using_a_java_library_class
 java_array = java.util.ArrayList.new
 assert_equal __, java_array.class
 end

 def test_java_class_can_be_referenced_using_both_ruby_and_java_like_syntax
 assert_equal __, Java::JavaUtil::ArrayList == java.util.ArrayList
 end

 def test_include_class_includes_class_in_module_scope
 assert_nil defined?(TreeSet)
 include_class "java.util.TreeSet"
 assert_equal __, defined?(TreeSet)
 end

 # THINK ABOUT IT:
 #
 # What if we use:
 #
 # include_class "java.lang.String"
 #
 # What would be the value of the String constant after this
 # include_class is run? Would it be useful to provide a way of
 # aliasing java classes to different names?

 JString = java.lang.String
 def test_also_java_class_can_be_given_ruby_aliases
 java_string = JString.new("A Java String")
 assert_equal __, java_string.class
 assert_equal __, JString
 end

 def test_can_directly_call_java_methods_on_java_objects
 java_string = JString.new("A Java String")
 assert_equal __, java_string.toLowerCase
 end

 def test_jruby_provides_snake_case_versions_of_java_methods
 java_string = JString.new("A Java String")
 assert_equal __, java_string.to_lower_case
 end

 def test_jruby_provides_question_mark_versions_of_boolean_methods
 java_string = JString.new("A Java String")
 assert_equal __, java_string.endsWith("String")
 assert_equal __, java_string.ends_with("String")
 assert_equal __, java_string.ends_with?("String")
 end

 def test_java_string_are_not_ruby_strings
 ruby_string = "A Java String"
 java_string = java.lang.String.new(ruby_string)
 assert_equal __, java_string.is_a?(java.lang.String)
 assert_equal __, java_string.is_a?(String)
 end

 def test_java_strings_can_be_compared_to_ruby_strings_maybe
 ruby_string = "A Java String"
 java_string = java.lang.String.new(ruby_string)
 assert_equal __, ruby_string == java_string
 assert_equal __, java_string == ruby_string

 # THINK ABOUT IT:
 #
 # Is there any possible way for this to be more wrong?
 #
 # SERIOUSLY, THINK ABOUT IT:
 #
 # Why do you suppose that Ruby and Java strings compare like that?
 #
 # ADVANCED THINK ABOUT IT:
 #
 # Is there a way to make Ruby/Java string comparisons commutative?
 # How would you do it?
 end

 def test_however_most_methods_returning_strings_return_ruby_strings
 java_array = java.util.ArrayList.new
 assert_equal __, java_array.toString
 assert_equal __, java_array.toString.is_a?(String)
 assert_equal __, java_array.toString.is_a?(java.lang.String)
 end

 def test_some_ruby_objects_can_be_coerced_to_java
 assert_equal __, "ruby string".to_java.class
 assert_equal __, 1.to_java.class
 assert_equal __, 9.32.to_java.class
 assert_equal __, false.to_java.class
 end

 def test_some_ruby_objects_are_not_coerced_to_what_you_might_expect
 assert_equal __, [].to_java.class == Java::JavaUtil::ArrayList
 assert_equal __, {}.to_java.class == Java::JavaUtil::HashMap
 assert_equal __, Object.new.to_java.class == Java::JavaLang::Object
 end

 def test_java_collections_are_enumerable
 java_array = java.util.ArrayList.new
 java_array << "one" << "two" << "three"
 assert_equal __, java_array.map { |item| item.upcase }
 end

 # ------------------------------------------------------------------

 # Open the Java ArrayList class and add a new method.
 class Java::JavaUtil::ArrayList
 def multiply_all
 result = 1
 each do |item|
 result *= item
 end
 result
 end
 end

 def test_java_class_are_open_from_ruby
 java_array = java.util.ArrayList.new
 java_array.add_all([1,2,3,4,5])

 assert_equal __, java_array.multiply_all
 end

end