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1、Type information,华南理工大学 计算机科学与工程学院 韦佳 ,The need for RTTI,/Shapes.java The upcast occurs when the shape is placed into the List. The RTTI occurs when you fetch an element out of the array. Polymorphism takes then.,The Class object,RTTI is accomplished through a special kind of object called the Class
2、 object, which contains information about the class. Each time you write and compile a new class, a single Class object is also created (stored in an identically named .class file). All classes are loaded into the JVM dynamically, upon the first use of a class.,Once the Class object for that type is
3、 in memory, it is used to create all objects of that type. /SweetShop.java One of the ways to get a reference to the Class object is the static forName() method. The call to forName() is being made for its side effect in the last example, which is to load the class Gum if it isnt already loaded.,If
4、you already have an object of the type youre interested in, you can fetch the Class reference by calling a method thats part of the Object root class: getClass(). /ToyTest.java,Class literals,Java provides a second way to produce the reference to the Class object: the class literal. FancyToy.class;
5、Creating a reference to a Class object using “.class” doesnt automatically initialize the Class object. /ClassInitialization.java,Generic class references,Using the generic syntax, you can constrain the type of Class object. /GenericClassReferences.java To loosen the constraints when using generic C
6、lass references, we can employ wildcard?. /WildcardClassReferences.java In order to create a Class reference that is constrainted to a type or any subtype, we can combine the wildcard with the extends keyword. /BoundedClassReferences.java,Checking before a cast,Theres a third form of RTTI in Java. This is the keyword instanceof, which tells you if an object is an instance of a particular type. Like this: if(x instanceof Dog) (Dog)x).bark(); /PetCreator.java; ForNameCreator.java; PetCount.java,To be continued,
