The package keyword specifies the Java package in which the classes declared in a Java source file reside.
package com.mycompany;
public class MyClass
{
}
The package statement, if present, must be the first non-comment text in a Java source file.
In the example above, the fully-qualified class name of the MyClass class is com.mycompany.MyClass.
If a Java source file does not contain a package statement, the classes defined in the file are in the default package. Note that classes in the default package may not be referenced from classes in non-default packages.