Packages and interfaces form a very important concept in Java. In our day to day life, as a software developer, sometimes we need to handle small projects and at other times, big projects. In small projects, it is a normal practice to keep all the related files in a single directory. For example, all Java files use a single directory, all CSS files in some other directory, etc. But as the number of files increase when the project becomes big, it really becomes difficult to maintain all the files in the same directory. In Java this problem can be avoided by the use of packages.