转载

编程语言对比手册－纵向版[-类-]

语言对比手册是我一直想写的一个系列:经过认真思考，我决定从纵向和横行两个方面

来比较Java，Kotlin，Javascript，C++，Python，Dart，六种语言。

纵向版按知识点进行划分，总篇数不定，横向版按语言进行划分，共6篇。其中:

Java基于jdk8
Kotlin基于jdk8
JavaScript基于node11.10.1，使用ES6+
C++基于C++14
Python基于Python 3.7.2
Dart基于Dart2.1.0
复制代码

别的先不说，helloworld走起

1.Java版：

public class Client {
    public static void main(String[] args) {
        System.out.println("HelloWorld");
    }
}
复制代码

2.Kotlin版：

fun main(args: Array<String>) {
    println("HelloWorld")
}
复制代码

3.JavaScript版：

console.log("HelloWorld");
复制代码

4.C＋＋版：

#include <iostream>

int main() {
    std::cout << "Hello, World!" << std::endl;
    return 0;
}
复制代码

5.Python版：

if __name__ == '__main__':
   print("HelloWorld")
复制代码

6.Dart版：

main() {
  print("HelloWorld");
}
复制代码

一、Java代码实现

怎么看都是我家Java的类最好看

1.类的定义和构造（析构）函数

定义一个Shape类,在构造方法中打印语句

|-- 类定义
public class Shape {
    public Shape() {//构造器
        System.out.println("Shape构造函数");
    }
}

|-- 类实例化
Shape shape = new Shape();
复制代码

2.类的封装（成员变量，成员方法）

私有成员变量+get+set+一参构造器+公共成员方法

public class Shape {
    private String name;
    public Shape(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void draw() {
        System.out.println("绘制" + name);
    }
    ...
}

|-- 使用
Shape shape = new Shape("Shape");
shape.draw();//绘制Shape
shape.setName("四维空间");
System.out.println(shape.getName());//四维空间
复制代码

3.类的继承

关键字 extends

public class Point extends Shape {
    public Point(String name) {
        super(name);
    }
    public int x;
    public int y;
}

|-- 使用 子类可使用父类的方法
Point point = new Point("二维点");
point.draw();//绘制二维点
System.out.println(point.getName());//二维点
复制代码

4.类的多态性

借用C++的一句话：父类指针指向子类引用

---->[Shape子类：Circle]--------------------------
public class Circle extends Shape {
    private int mRadius;

    public int getRadius() {
        return mRadius;
    }

    public void setRadius(int radius) {
        mRadius = radius;
    }

    public Circle() {
    }

    public Circle(String name) {
        super(name);
    }

    @Override
    public void draw() {
        System.out.println("Draw in Circle");
    }
}

---->[Shape子类：Point]--------------------------
public class Point extends Shape {
    public Point() {
    }
    public Point(String name) {
        super(name);
    }
    public int x;
    public int y;
    @Override
    public void draw() {
       System.out.println("Draw in Point");
    }
}

---->[测试函数]--------------------------
private static void doDraw(Shape shape) {
    shape.draw();
}

|-- 相同父类不同类对象执行不同方法
Shape point = new Point();
doDraw(point);//Draw in Point
Shape circle = new Circle();
doDraw(circle);//Draw in Circle
复制代码

5.其他特性

|--- 抽象类
public abstract class Shape {
    ...
    public abstract void draw();
    ...
}

|--- 接口
public interface Drawable {
    void draw();
}

|--- 类实现接口
public class Shape implements Drawable {
复制代码

二、Kotlin代码实现

冉冉升起的新星，功能比java胖了一大圈，就是感觉挺乱的...

1.类的定义和构造（析构）函数

|-- 类定义
open class Shape {
    constructor() {
        println("Shape构造函数")
    }
    
    //init {//init初始化是时也可执行
    //    println("Shape初始化")
    //}
}

|-- 类实例化
val shape = Shape()//形式1
val shape: Shape = Shape()//形式2
复制代码

2.类的封装（成员变量，成员方法）

|-- 方式一：构造方法初始化
class Shape {
    var name: String? = null
    constructor(name: String) {
        this.name = name
    }
    fun draw() {
        println("绘制" + name!!)
    }
    ...
}

|-- 方式二：使用初始化列表
class Shape (name: String) {
    var name = name
    fun draw() {
        println("绘制" + name)
    }
}

|-- 使用
val shape = Shape("Shape")
shape.draw()//绘制Shape
shape.name="四维空间"
System.out.println(shape.name)//四维空间
复制代码

3.类的继承

|-- 继承-构造函数
class Point : Shape {
    var x: Int = 0
    var y: Int = 0
    constructor(name: String) : super(name) {}
    override fun draw() {
        println("Draw in Point")
    }
}

|-- 继承-父构造器
class Circle(name: String) : Shape(name) {
    var radius: Int = 0

    override fun draw() {
        println("Draw in Circle")
    }
}

|--使用
val point = Point("二维点");
point.draw();//绘制二维点
System.out.println(point.name);//二维点
复制代码

4.类的多态性

doDraw(Point("Point"));//Draw in Point
doDraw(Circle("Circle"));//Draw in Circle

fun doDraw(shape: Shape) {
    shape.draw()
}
复制代码

5.其他特性

|--- 抽象类
abstract class Shape (name: String) {
    var name = name
    abstract fun draw();
}

|--- 接口
interface Drawable {
    fun draw()
}

|--- 类实现接口
open class Shape(name: String) : Drawable {
复制代码

三、JavaScript代码实现

1.类的定义和构造（析构）函数

|-- 类定义
class Shape {
    constructor() {//构造器
        console.log("Shape构造函数");
    }
}
module.exports = Shape;

|-- 类实例化
const Shape = require('./Shape');

let shape = new Shape();
复制代码

2.类的封装（成员变量，成员方法）

|-- 简单封装
class Shape {
    get name() {
        return this._name;
    }
    set name(value) {
        this._name = value;
    }
    constructor(name) {
        this._name = name;
    }
    draw() {
        console.log("绘制" + this._name);
    }
}
module.exports = Shape;

|-- 使用
let shape = new Shape("Shape");
shape.draw();//绘制Shape
shape.name = "四维空间";
console.log(shape.name);//四维空间
复制代码

3.类的继承

---->[Point.js]-----------------
const Shape = require('./Shape');
class Point extends Shape {
    constructor(name) {
        super(name);
        this.x = 0;
        this.y = 0;
    }
    draw() {
        console.log("Draw in " + this.name);
    }
}
module.exports = Point;

---->[Circle.js]-----------------
const Shape = require('./Shape');
class Circle extends Shape {
    constructor(name) {
        super(name);
        this.radius = 0;
    }
    draw() {
        console.log("Draw in " + this.name);
    }
}
module.exports = Circle;

|-- 使用
const Point = require('./Point');
const Circle = require('./Circle');

let point =new Point("Point");
point.draw();//Draw in Point
point.x = 100;
console.log(point.x);//100

let circle =new Circle("Circle");
circle.draw();//Draw in Circle
circle.radius = 100;
console.log(circle.radius);//100
复制代码

4.类的多态性

这姑且算是多态吧...

doDraw(new Point());//Draw in Point
doDraw(new Circle());//Draw in Circle

function doDraw(shape) {
    shape.draw();
}
复制代码

二、C＋＋代码实现

1.类的定义和构造（析构）函数

---->[Shape.h]-----------------
#ifndef C_SHAPE_H
#define C_SHAPE_H
class Shape {
public:
    Shape();
    ~Shape();
};
#endif //C_SHAPE_H

---->[Shape.cpp]-----------------
#include "Shape.h"
#include <iostream>
using namespace std;

Shape::Shape() {
    cout << "Shape构造函数" << endl;
}
Shape::~Shape() {
    cout << "Shape析造函数" << endl;
}

|-- 类实例化
Shape shape;//实例化对象

Shape *shape = new Shape();//自己开辟内存实例化
delete shape;
shape = nullptr;
复制代码

2.类的封装（成员变量，成员方法）

---->[Shape.h]-----------------
...
#include <string>
using namespace std;
class Shape {
public:
    ...
    string &getName();
    Shape(string &name);
    void setName(string &name);
    void draw();
private:
    string name;
};
...

---->[Shape.cpp]-----------------
...
string &Shape::getName() {
    return name;
}
void Shape::setName(string &name) {
    Shape::name = name;
}
Shape::Shape(string &name) : name(name) {}
void Shape::draw() {
    cout << "draw " << name << endl;
}


|-- 使用(指针形式)
Shape *shape = new Shape();
string name="four side space";
shape->setName(name);
shape->draw();//draw four side space
delete shape;
shape = nullptr;
复制代码

3.类的继承

---->[Point.h]------------------
#ifndef CPP_POINT_H
#define CPP_POINT_H
#include "Shape.h"
class Point : public Shape{
public:
    int x;
    int y;
    void draw() override;
};
#endif //CPP_POINT_H

---->[Point.cpp]------------------
#include "Point.h"
#include <iostream>
using namespace std;
void Point::draw() {
    cout << "Draw in Point" << endl;
}



|-- 使用
Point *point = new Point();
point->draw();//Draw in Point
point->x = 100;
cout <<  point->x << endl;//100
复制代码

4.类的多态性

---->[Circle.h]------------------
#ifndef CPP_CIRCLE_H
#define CPP_CIRCLE_H
#include "Shape.h"
class Circle : public Shape{
public:
    void draw() override;
private:
    int mRadius;
    
};
#endif //CPP_CIRCLE_H

---->[Circle.cpp]------------------
#include "Circle.h"
#include <iostream>
using namespace std;
void Circle::draw() {
    cout << "Draw in Point" << endl;
}

|-- 使用
Shape *point = new Point();
Shape *circle = new Circle();
doDraw(point);
doDraw(circle);

void doDraw(Shape *pShape) {
    pShape->draw();
}
复制代码

5.其他特性

|-- 含有纯虚函数的类为抽象类
---->[Shape.h]----------------
...
virtual void draw() const = 0;
...

|-- 子类需要覆写纯虚函数，否则不能直接实例化
---->[Circle.h]----------------
... 
public:
    void draw() const override;
...
复制代码

五、Python代码实现

1.类的定义和构造函数

|-- 类定义
class Shape:
    def __init__(self):
        print("Shape构造函数")

|-- 类实例化
from python.Shape import Shape
shape = Shape()
复制代码

2.类的封装（成员变量，成员方法）

---->[Shape.py]-----------------
class Shape:
    def __init__(self, name):
        self.name = name
        print("Shape构造函数")

    def draw(self):
        print("draw " + self.name)

|-- 使用
shape = Shape("Shape")
shape.draw()#draw Shape
shape.name="四维空间"
shape.draw()#draw 四维空间
复制代码

3.类的继承

---->[Point.py]------------------
from python.Shape import Shape

class Point(Shape):
    def __init__(self, name):
        super().__init__(name)
        self.x = 0
        self.y = 0
    def draw(self):
        print("Draw in Point")

|-- 使用
point = Point("Point")
point.draw()#Draw in Point
point.x=100
print(point.x)#100
复制代码

4.类的多态性

---->[Circle.py]------------------

from python.Shape import Shape
class Circle(Shape):
    def __init__(self, name):
        super().__init__(name)
        self.radius = 0
    def draw(self):
        print("Draw in Circle")

|-- 使用
def doDraw(shape):
    shape.draw()

doDraw(Point("Point"))#Draw in Point
doDraw(Circle("Circle"))#Draw in Circle
复制代码

六、Dart代码实现

1.类的定义和构造函数

|-- 类定义
class Shape {
  Shape() {
    print("Shape构造函数");
  }
}

|-- 类实例化
import 'Shape.dart';
var shape = Shape();
复制代码

2.类的封装（成员变量，成员方法）

---->[Shape.dart]-----------------
class Shape {
  String name;
  Shape(this.name);

  draw() {
    print("draw " +name);
  }
}

|-- 使用
var shape = Shape("Shape");
shape.draw();//draw Shape
shape.name="四维空间";
shape.draw();//draw 四维空间
复制代码

3.类的继承

---->[Point.dart]------------------
import 'Shape.dart';
class Point extends Shape {
  Point(String name) : super(name);
  int x;
  int y;
  @override
  draw() {
    print("Draw in Point");
    
  }
}

|-- 使用
var point = Point("Point");
point.draw();//Draw in Point
point.x=100;
print(point.x);//100
复制代码

4.类的多态性

---->[Circle.dart]------------------
import 'Shape.dart';
class Circle extends Shape {
  Circle(String name) : super(name);
  int radius;
  @override
  draw() {
    print("Draw in Circle");
  }
}

|-- 使用
doDraw(Point("Point"));//Draw in Point
doDraw(Circle("Circle"));//Draw in Circle

void doDraw(Shape shape) {
  shape.draw();
}
复制代码

5.其他特性

|-- 抽象类
---->[Drawable.dart]----------------
abstract class Drawable {
    void draw();
}
...

|-- 实现
---->[Shape.dart]----------------
import 'Drawable.dart';
class Shape implements Drawable{
  String name;
  Shape(this.name);
  @override
  void draw() {
    print("draw " +name);
  }
}
复制代码