# OOAD Lab 4, 5 (03/16)
###### tags: `OOAD`

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## 4. Multiple Inheritance (in C++ and Java)
- **Percolating upward**
- e.g. 將有需要的 virtual function 向上移
- If we percolated up more methods as we built these classes, Car becomes bloated and confused. Generally, only functionality common to all subclasses belongs in a base class.
- **Runtime Type Identification (RTTI)**
- **This means that as a program is running it is possible to determine the exact type of object a pointer or reference refers to.**
- **casting down**
- We have casted a base class pointer down its hierarchy into a subclass pointer.
- **C++: `Sub* sub_ptr = dynamic_cast<Sub*>(base_ptr);`**
- **java: `if(obj instanceof Sub) ...`**
- **Explicitly checking an objects type is usually indicative of bad design**
- **spaghetti code**
- **無法做到與未來擴充的型別無關**
- **Vehicle <- Car, Vehicle <- Jet, JetCar <- (Jet, Car)**
- **JetCar called Vehicle's constructor twice**
- **Ambiguity can happen when you use multiple inheritance**
1. **Ambiguity can happen when you use multiple inheritance**
- **C++: `sub_ptr->Base::foo()`**
2. **Override**
- **解決重複基底類別繼承：**
- **鑽石形繼承 diamond-shaped inheritance**
- **C++:**

        class Sub1 : virtual Base {};
        class Sub2 : virtual Base {};
        class SubSub : Sub1, Sub2 {};

- **Java Interface**
- **Java prohibits multiple inheritance**
- **Only virtual function declarations** in interfaces
- **Java:**

        interface Foo {
            void bar();
        }
        class Sub extends Base implements Foo {}

- **In principle, implementing an interface has loosen inheritance principle to follow because there is no attributes (variables) to inherit from implement**
- **~~is-a~~ ---> can-do**

## 5. Comparison of C++ and Java

| human |
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| human |
| student |
| human |
| teacher |
| 講師 |