【Lua】题目小练7

Lua实现类、以及类的继承：

Point = {}
Point.__index = Point

function Point:new(x1, y1)
    local obj = {x = x1 or 0, y = y1 or 0}
    setmetatable(obj,self)
    return obj
end

function Point:describe()
    print(string.format("Point at (%d, %d)", self.x, self.y))
end


-- 定义子类Distance，继承Point
Distance = setmetatable({},{__index = Point})
Distance.__index = Distance

function Distance:new(x,y)
    local obj = Point.new(self, x, y)
    setmetatable(obj, self)
    return obj
end

function Distance:distanceTo(other)
    local dx = self.x - other.x
    local dy = self.y - other.y
    return math.sqrt(dx * dx + dy * dy)
end

local p1 = Distance:new(0, 0)
local p2 = Distance:new(1, 1)

p1:describe()
p2:describe()

print(p1:distanceTo(p2))

-- 题目一：封装一个矩形类

-- 要求：

-- 类名：Rectangle

-- 属性：width, height（默认值都是 0）

-- 方法：

-- area()：返回面积

-- perimeter()：返回周长

local Rectangle = {}
Rectangle.__index = Rectangle

function Rectangle:new(w, h)
    local obj = {
        w = (w and w > 0) and w or 0,
        h = (h and h > 0) and h or 0
    }
    setmetatable(obj, Rectangle)
    return obj
end

function Rectangle:area()
    return self.w * self.h
end

function Rectangle:perimeter()
    return 2 * (self.w + self.h)
end

local obj = Rectangle:new(2,3)
print(obj:area())
print(obj:perimeter())

-- 题目二：实现一个继承关系

-- 要求：

-- 基类：Shape

-- 方法：describe()，输出 "This is a shape."

-- 子类：Circle

-- 属性：radius

-- 重写 describe()，输出 "This is a circle with radius R"

-- 添加方法：area()（使用 π≈3.14）

local Shape = {}
Shape.__index = Shape

function Shape:describe()
    print("This is a shape.")
end

local Circle = setmetatable({}, {__index = Shape})
Circle.__index = Circle

function Circle:new(radius)
    local obj = {
        radius = (radius and radius > 0) and radius or 1 --默认值为1
    }
    setmetatable(obj, self)
    return obj
end

function Circle:describe()
    print("This is a circle with radius " .. self.radius)
end

function Circle:area()
    return 3.14 * self.radius ^ 2
end

local obj = Circle:new(2)
obj:describe()
print(obj:area())

-- 题目三：多级继承

-- 要求：

-- Animal 基类，有属性 name，方法 speak() 打印 "Some generic animal sound"

-- Dog 继承 Animal，重写 speak() 输出 "Woof!"

-- Sheepdog 再继承 Dog，增加方法 guard() 输出 "Guarding the sheep!"

local Animal = {}
Animal.__index = Animal

function Animal:new(name)
    local obj = {
        name = name or "UnKnow"
    }
    setmetatable(obj, self)
    return obj
end

function Animal:speak()
    print("Some generic animal sound")
end

local Dog = setmetatable({},{__index = Animal})
Dog.__index = Dog

function Dog:new(name)
    return Animal.new(self,name)
end

function Dog:speak()
    print("Woof")
end

local Sheepdog = setmetatable({},{__index = Dog})
Sheepdog.__index = Sheepdog

function Sheepdog:new(name)
    return Dog.new(self,name)
end

function Sheepdog:guard()
    print("Guarding the sheep!")
end

local obj = Sheepdog:new("ASheepdog")
obj:speak()
obj:guard()