Abstract Data Types 抽象数据类型.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Type system in PL: Abstraction, Safety, Optimization, Documentation * * * * * * * * * * * * * * * * * * * * * An Example in C++ class stack { private: int *stackPtr, maxLen, topPtr; public: stack() { // a constructor stackPtr = new int [100]; maxLen = 99; topPtr = -1; }; ~stack () {delete [] stackPtr;}; void push (int num) {…}; void pop () {…}; int top () {…}; int empty () {…}; } 鼓励声明和实现分离 C++也存在声明中有私有表示的问题，如何弥补？ Evaluation of ADTs in C++ and Ada C++ support for ADTs is similar to expressive power of Ada Both provide effective mechanisms for encapsulation and information hiding Ada packages are more general encapsulations; classes are types Language Examples: C++ (continued) Friend functions or classes - to provide access to private members to some unrelated units or functions Necessary in C++ Language Examples: Java Similar to C++, except: All user-defined types are classes All objects are allocated from the heap and accessed through reference variables Individual entities in classes have access control modifiers (private or public), rather than clauses Java has a second scoping mechanism, package scope, which can be used in place of friends All entities in all classes in a package that do not have access control modifiers are visible throughout the package An Example in Java class StackClass { private int [] stackRef; private int [] maxLen, topIndex; public StackClass() { // a constructor stackRef = new int [100]; maxLen = 99; topPtr = -1; }; public void push (int num) {…}; public void pop () {…}; public int top () {…}; public boolean empty () {…}; } Language Examples: C# Based on C++ and Java Adds two access modifiers, internal and protected internal All class instances are heap dynamic Default constructors are available for all classes Garbage collection is used for most heap objects, so destructors ar