Java™ Application Development on Linux - Dator

3.4 Encapsulation, Inheritance, and Polymorphism85is reminiscent of the C/C++ include preprocessor directive, their function isnot the same. An import statement does not include any new code; it only aidsname resolution. Secondly, the “*” can only be used at the end of the packagename; it is not a true wildcard in the regular expression sense of the word.Thirdly, every class has what is in effect an implicit import java.lang.* sothat you don’t need to put one there. References to String or System or othercore language classes can be made without the need for either the importstatement or the fully qualified name (except as described in the nextparagraph).If you need to use two different classes that have the same name but comefrom different packages, you will still need to refer to them by their full names;import can’t help you here. As an example of this, consider the two classesjava.util.Date and java.sql.Date (though with any luck you won’t needto refer to both of them within the same class).3.4ENCAPSULATION, INHERITANCE, AND POLYMORPHISMThe classic troika of OOP buzzwords is “encapsulation, inheritance, andpolymorphism.” How does Java do each of these things?3.4.1 EncapsulationEncapsulation is the grouping of data and algorithms together into units, andit’s also about hiding implementation details that are not important to the usersof the unit. The basic unit of encapsulation is the class. All Java code exists inclasses. A class is declared with the class keyword (Example 3.24).Example 3.24 A sample Java class declaration that doesn’t actually do anything usefulpublic classSample{private int id;}public void method(){System.out.println(id);}