Day 1, 2, 28 and 31 added (java)

[thefluffyoshi]

Please make sure you have done the following:

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

[aaditkamat]

Also make sure you add only the solutions for the day you have mentioned in the title of the PR.