1 Package: Package is to ensure that the software has a good modular basis, is to achieve the software components of the "high cohesion", "low coupling." In the programming of Face objects, the object is the most basic unit of encapsulation.
2 Inheritance: When defining and implementing a class, you can do it on the basis of an existing class, the content defined by the already existing class as its own content, and can add a number of new content, or modify the original method to make it more suitable for special needs, which is inheritance.
3 polymorphic: Polymorphism refers to the specific class that the reference variable is defined in the program and the method call made through the reference variable, which is not deterministic in programming, but is determined during run time in the program, where a reference variable actually points to the instance object of that class.
Java Development 1. Three main features of object-oriented