Suppose you are two Software Developers- X and Y.

1. X will create a Java Project called MyFancyJavaProject and write up a simple Java program without following the Singleton pattern.
2. Later, X needs to create a local Git Repository with the MyFancyJavaProject and connect it to a new GitHub Repository.
3. X will work on the main branch, commit his changes on Jan 6, and push it to the origin.
4. X will then invite the second developer Y, to collaborate with his project.
5. Y will clone the whole project into his local machine and create a new branch called branchY.
6. Now, Y will checkout to branchY and modify the program to implement Singleton Pattern, commit his changes on Jan 8, and push it to the origin.
7. Meanwhile, X will make some slight changes to his code, commit the changes on Jan 9, and then push them to the origin.
8. Y will check out to the main branch, pull the latest changes from origin and create a new branch called branchXY.
9. Then Y will checkout to branchXY and merge this branch with branchY. After merging, if any conflict arises, he needs to resolve them (e.g., he can keep the codes from branchY).
10. Finally, Y will commit the changes on Jan 11, and then push them to the origin.

Use appropriate commit messages.