1. forced coercion

~/projects/jruby ➔ jirb
irb(main):001:0> require 'java'
=> true
irb(main):002:0> 'foo'.to_java.class
=> Java::JavaLang::String
irb(main):003:0> 1.to_java.class
=> Java::JavaLang::Long
irb(main):004:0> [1,2,3].to_java.class
=> #<Class:01xb95f72>
irb(main):005:0> Object.new.to_java.class
=> Java::OrgJruby::RubyObject
irb(main):006:0> STDIN.to_java.class
=> Java::OrgJruby::RubyIO

2. example bench

~/projects/jruby ➔ jruby -rjava -rbenchmark -e "import java.lang.System; 10.times { puts Benchmark.measure { a = 'foo'; 1_000_000.times { System.get_property a } } }
> "
  1.122000   0.000000   1.122000 (  1.098000)
  1.069000   0.000000   1.069000 (  1.069000)
  1.056000   0.000000   1.056000 (  1.056000)
  1.081000   0.000000   1.081000 (  1.081000)
  1.057000   0.000000   1.057000 (  1.057000)
  1.056000   0.000000   1.056000 (  1.056000)
  1.055000   0.000000   1.055000 (  1.055000)
  1.060000   0.000000   1.060000 (  1.061000)
  1.072000   0.000000   1.072000 (  1.072000)
  1.071000   0.000000   1.071000 (  1.071000)

~/projects/jruby ➔ jruby -rjava -rbenchmark -e "import java.lang.System; 10.times { puts Benchmark.measure { a = 'foo'.to_java; 1_000_000.times { System.get_property a } } }
"
  0.880000   0.000000   0.880000 (  0.857000)
  0.800000   0.000000   0.800000 (  0.800000)
  0.796000   0.000000   0.796000 (  0.796000)
  0.797000   0.000000   0.797000 (  0.797000)
  0.801000   0.000000   0.801000 (  0.801000)
  0.799000   0.000000   0.799000 (  0.799000)
  0.803000   0.000000   0.803000 (  0.803000)
  0.801000   0.000000   0.801000 (  0.801000)
  0.806000   0.000000   0.806000 (  0.806000)
  0.815000   0.000000   0.815000 (  0.815000)

~/projects/jruby ➔ jruby -rjava -rbenchmark -e "import java.lang.System; 10.times { puts Benchmark.measure { a = 'foo'.to_java; 1_000_000.times { System } } }
"
  0.325000   0.000000   0.325000 (  0.302000)
  0.275000   0.000000   0.275000 (  0.275000)
  0.279000   0.000000   0.279000 (  0.279000)
  0.274000   0.000000   0.274000 (  0.274000)
  0.279000   0.000000   0.279000 (  0.279000)
  0.279000   0.000000   0.279000 (  0.279000)
  0.279000   0.000000   0.279000 (  0.280000)
  0.276000   0.000000   0.276000 (  0.277000)
  0.274000   0.000000   0.274000 (  0.274000)
  0.274000   0.000000   0.274000 (  0.274000)