Merge pull request #175 from jintaoguan/master

java code for chapter4
Merge pull request #176 from jintaoguan/master

java code for the first solution of Chapter6
update ignore file
ruby version code for 4,5,6 and 7
Ignore build target folder.
update ruby version code
fix code issues and update comments
Merge pull request #178 from UncleBill/master

Ignore build target folder.
Merge pull request #177 from RONGHAI/master

Ruby Version Code Update