Day 1, Day 2, and Day 4 added (java)

[JaquelineGomez]

Please make sure you have done the following:

• Created a folder with the name of language you code inside directory for the day you are making the contribution to
• Added the source code file inside /Day<n>/<Language>/
• Tested your code
• Added credits (author and date) at the top of the code
• Updated README.md for /Day <n>/
• Added yourself as a contributor using all-contributors-cli