These are few projects created while initially learning Java and are meant for others to learn from it.
While creating or editing the file keep in mind to have the name of class containing the main class to be the same as the name of the file.
Also, here, the number in the name of solution files is of the i-1th tutorial. Eg. the lab2a.java file will be actually practice problem 1a.
To run a java file in command line use the following steps:
javac filename.java
java classname