里氏替换原则
- 类图对比

里氏替换原则

所有引用基类的地方必须能透明地使用其子类的对象，也就是说子类对象可以替换其父类对象，而程序执行效果不变。

解读： 在继承体系中，子类中可以增加自己特有的方法，也可以实现父类的抽象方法，但是不能重写父类的非抽象方法，否则该继承关系就不是一个正确的继承关系。

类图对比

未实践里氏替换原则：

//================== Rectangle.h ==================

@interface Rectangle : NSObject
{
@protected double _width;
@protected double _height;
}

//设置宽高
- (void)setWidth:(double)width;
- (void)setHeight:(double)height;

//获取宽高
- (double)width;
- (double)height;

//获取面积
- (double)getArea;

@end



//================== Rectangle.m ==================

@implementation Rectangle

- (void)setWidth:(double)width{
    _width = width;
}

- (void)setHeight:(double)height{
    _height = height;
}

- (double)width{
    return _width;
}

- (double)height{
    return _height;
}


- (double)getArea{
    return _width * _height;
}

@end

//================== Square.h ==================

@interface Square : Rectangle
@end

//================== Square.m ==================

@implementation Square

- (void)setWidth:(double)width{
    
    _width = width;
    _height = width;
}

- (void)setHeight:(double)height{
    
    _width = height;
    _height = height;
}

@end

实践了里氏替换原则：

//================== Quadrangle.h ==================

@interface Quadrangle : NSObject
{
@protected double _width;
@protected double _height;
}

- (void)setWidth:(double)width;
- (void)setHeight:(double)height;

- (double)width;
- (double)height;

- (double)getArea;
@end

//================== Rectangle.h ==================

#import "Quadrangle.h"

@interface Rectangle : Quadrangle

@end



//================== Rectangle.m ==================

@implementation Rectangle

- (void)setWidth:(double)width{
    _width = width;
}

- (void)setHeight:(double)height{
    _height = height;
}

- (double)width{
    return _width;
}

- (double)height{
    return _height;
}


- (double)getArea{
    return _width * _height;
}

@end

//================== Square.h ==================

@interface Square : Quadrangle
{
    @protected double _sideLength;
}

-(void)setSideLength:(double)sideLength;

-(double)sideLength;

@end



//================== Square.m ==================

@implementation Square

-(void)setSideLength:(double)sideLength{    
    _sideLength = sideLength;
}

-(double)sideLength{
    return _sideLength;
}

- (void)setWidth:(double)width{
    _sideLength = width;
}

- (void)setHeight:(double)height{
    _sideLength = height;
}

- (double)width{
    return _sideLength;
}

- (double)height{
    return _sideLength;
}


- (double)getArea{
    return _sideLength * _sideLength;
}

@end

里氏替换原则

类图对比

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