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Understanding Inheritance and LSP in Programming

Delve into the concepts of inheritance and Liskov Substitution Principle in programming. Learn how to avoid "reinventing the wheel" and the importance of software design principles. Explore the differences between inheritance, delegation, and aggregation.

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Understanding Inheritance and LSP in Programming

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  1. More Inheritance and LSP CS340100, NTHU Yoshi

  2. More about Inheritance • Reuse? • Q1: 你有沒有程式”砍掉重練”的經驗? • Q2: 你有沒有”再造輪子”的經驗? • class Rectangle • Firstly, we only have this design, and the system was developed • class Square • Then, we have the requirement of Square, and we wrote a class Square • Square “IS A” kind of rectangle

  3. Class Rectangle class Rectangle {double width;double height;publicdoublegetHeight() {return height;    }publicvoidsetHeight(double height) {this.height = height;    }publicdoublegetWidth() {return width;    }publicvoidsetWidth(double width) {this.width = width;    }   }

  4. Class Square class Square extends Rectangle {publicvoidsetHeight(double height) {super.setHeight(height);super.setWidth(height);    }publicvoidsetWidth(double width) {super.setHeight(width);super.setWidth(width);    }}

  5. For Instance… void g(Rectangle r) {r.setWidth(5);r.setHeight(4);    if (r.getWidth() * r.getHeight() != 20) {        throw new RuntimeException();    }} //some other place Rectangle square = new Square(); g(square);

  6. Liskov Substitution Principle (LSP) • Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it • Very difficult problem!! • Further study: OOAD • Software design principals • Please google it if you are interested in it • One of the principals • Prefer Composition over inheritance • Why? Can you give an example?

  7. Delegation Aggregation Inheritance

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