Java is case sensitive. As far as Java is concerned there is no relation whatsoever between the uppercase letter and lower case letter.
The First character of any name can be a upper case letter or a lower case letter a $ sign or an underscore character.
a-z A-Z $ _
The characters in a name can be anything that the first character can be and also be can any digit.
a-z A-Z $ _ 0-9
Class and Interface Names
The names of classes and interfaces are usually in mixed case and begin with a capital letter. These are some examples of class names in the Java API.
Members of classes, methods, data items and such are also in mixed case but the usually begins with a lower case letter. These are some examples of class members.
The naming convention for constant is that they are usually named with all upper case letters. These also have a tendancy to include the underscore character.