文章目录

• 前言
• 问题一
• • 问题描述
  • Java
  • C++
• 问题二
• • 题目描述
  • Java
  • • ZPoint.java
    • Test.java
  • C++
  • • ZPoint.h
    • ZPoint.cpp
    • Test.cpp
• 问题三
• • 问题描述
  • C++
  • • GeometricObject.h
    • GeometricObject.cpp
    • GeoAreaSum.cpp
  • Java
  • • GeometricObject.java
    • Circle.java
    • Rectangle.java
    • Cylinder.java
    • GeoAreaSum.java
• 参考资料

前言

前段时间有一个面试要考Java，在翻复习资料时，发现了三道题（谢谢张老师）基本上概括了一个语言的常用语法。特此记录，围绕这三道题用不同的语言编写，以便后续进行快速地复习。如果想要详细复习，请看C/C++要点复习

问题一

问题描述

请从控制台输入一个三角形的三条边长，并判断这三条边能不能构成一个三角形。

如能构成，请打印输出这个三角形的周长（要求输出宽度为8，保留两位小数），如不能构成，请打印输出具体提示。

考察点：输入、输出、if条件判断

Java

public class TestTriangle {public static void main(String[] args) {double []a = new double[3];Scanner scanner = new Scanner(System.in);for (int i = 0; i < 3; i++) {System.out.print("第"+ (i+1) + "条边的边长：");a[i] = scanner.nextDouble();}Arrays.sort(a);if (a[0] + a[1] > a[2]) {double c = a[0]+a[1]+a[2];System.out.printf("三角形的周长为：%8.2f\n", c);} else {System.out.println("无法构成三角形");}}
}

C++

#include 
#include 
using namespace std;int main() {double a[3];for (int i = 0; i < 3; i++) {cout << "第" << i + 1 << "条边的边长：";cin >> a[i];}sort(a, a + 3);if (a[0] + a[1] > a[2]) {double c = a[0] + a[1] + a[2];printf("三角形的周长为： % 8.2f\n", c);}else {printf("无法构成三角形");}return 0;
}

问题二

题目描述

编写一个ZPoint类，其中包括：

• 两个私有成员double型变量x、y
• 一个构造方法ZPoint(double x,double y)
• 两个访问器分别访问x和y
• 一个静态方法distance(ZPoint p,ZPoint q)计算两点p、q的距离
• 一个实例方法distance(double x,double y)计算形参定义的点与当前点对象之间的距离。

在此基础上再编写一个测试类Test，用ZPoint实例化两个点对象（11,9）和（100,21.5），然后打印输出这两个点对象之间的距离，此外打印输出点对象（11,9）与x=71,y=19所定义的点的距离。

考察点：类的定义与创建、实例方法、静态方法

Java

ZPoint.java

public class ZPoint {private double x;private double y;public ZPoint(double x, double y) {this.x = x;this.y = y;}public double getX() {return x;}public double getY() {return y;}public static double distance(ZPoint p, ZPoint q) {double disX = Math.abs(p.getX() - q.getX());double disY = Math.abs(p.getY() - q.getY());double dis = Math.sqrt(disX*disX + disY*disY);return dis;}public double distance(double x, double y) {double disX = Math.abs(this.x - x);double disY = Math.abs(this.y - y);double dis = Math.sqrt(disX*disX + disY*disY);return dis;}
}

Test.java

public class Test {public static void main(String[] args) {ZPoint p1 = new ZPoint(11, 9);ZPoint p2 = new ZPoint(100, 21.5);System.out.println("两个点对象之间的距离为:");System.out.println(ZPoint.distance(p1, p2));System.out.println("点对象（11,9）与x=71,y=19所定义的点的距离为：");System.out.println(p1.distance(71,19));}
}

C++

当在类的外部定义静态成员时，不能重复static关键字
该关键字只能出现在类内部的声明语句

ZPoint.h

#ifndef ZPOINT_H
#define ZPOINT_H
#include 
using namespace std;class ZPoint
{
public:ZPoint(double x, double y);double getX();double getY();double distance(double x, double y);static double distance(ZPoint& p, ZPoint& q);
private:double x;double y;
};#endif 

ZPoint.cpp

#include "ZPoint.h"
#include ZPoint::ZPoint(double x, double y) {this->x = x;this->y = y;
}double ZPoint::getX() {return this->x;
}double ZPoint::getY() {return this->y;
}double ZPoint::distance(double x, double y) {double disX = abs(this->x - x);double disY = abs(this->y - y);double dis = sqrt(disX * disX + disY * disY);return dis;
}// 当在类的外部定义静态成员时，不能重复static关键字
// 该关键字只能出现在类内部的声明语句
double ZPoint::distance(ZPoint& p, ZPoint& q) {double disX = abs(p.getX() - q.getX());double disY = abs(p.getY() - q.getY());double dis = sqrt(disX * disX + disY * disY);return dis;
}

Test.cpp

#include 
#include "ZPoint.h"int main() {ZPoint p1(11, 9);ZPoint p2(100, 21.5);cout << "两个点对象之间的距离为：" << endl;cout << ZPoint::distance(p1, p2) << endl;cout << "点对象（11,9）与x=71,y=19所定义的点的距离为：" << endl;cout << p1.distance(71, 19) << endl;return 0;
}

问题三

问题描述

请运用面向对象程序设计思想编写完成几何对象的面积计算程序，具体要求为：GeometricObject（抽象类）、Circle、Cylinder和Rectangle之间的继承关系如下图所示，

请分按类图分别实现这四个类；

然后编写一测试类GeoAreaSum，在该类中编写一个方法求数组中所有几何对象的面积之和，其方法头为：sumArea(GeometricObject[ ] a)

再在GeoAreaSum的main方法中创建一个包括三个对象（一个半径为5的圆、一个半径为10、高为5的圆柱体和一个宽和高分别为6和8的矩形）的GeometricObject数组，使用sumArea方法计算出它们的总面积并在屏幕上打印输出。

(2) 另请思考如果将Cylinder与GeometricObject的继承关系改成与Cylinder与Circle的继承关系，同时将Cylinder中的私有变量r去掉，Cylinder又该如何编写？

考察点：继承、多态、接口、抽象类、虚函数，纯虚函数、虚基类

C++

如果子类调用父类带参数的构造方法，只能使用列表生成式

GeometricObject.h

#ifndef GEOMETRIC_H
#define GEOMETRIC_H
#include 
#include 
#define PI acos(-1)
using namespace std;class GeometricObject
{
public:virtual double findArea() = 0;virtual double findPerimeter() = 0;virtual ~GeometricObject() { }
};class Circle : public GeometricObject
{
public:Circle();Circle(double r);double getR();double findArea();double findPerimeter();
private:double r;
};class Rectangle : public GeometricObject
{
public:Rectangle();Rectangle(double w, double h);double findArea();double findPerimeter();
private:double w;double h;
};class Cylinder : public Circle
{
public:Cylinder();Cylinder(double h, double r);double findArea();double findPerimeter();
private:double h;
};// 需要使用指针数组
double sumArea(GeometricObject *a[], int n);
#endif // !GEOMETRIC_H

GeometricObject.cpp

#include "GeometricObject.h"Circle::Circle() {this->r = 0;
}Circle::Circle(double r) {this->r = r;
}double Circle::getR() {return this->r;
}double Circle::findArea() {return PI * r * r;
}double Circle::findPerimeter() {return 2 * PI * r;
}Rectangle::Rectangle() {this->w = 0;this->h = 0;
}Rectangle::Rectangle(double w, double h) {this->w = w;this->h = h;
}double Rectangle::findArea() {return w * h;
}double Rectangle::findPerimeter() {return 2 * (w + h);
}Cylinder::Cylinder(): Circle(0) {this->h = 0;
}// 如果子类调用父类带参数的构造方法，只能使用列表生成式
Cylinder::Cylinder(double h, double r) : Circle(r) {this->h = h;
}double Cylinder::findArea() {return 2 * PI * getR() * h + 2 * PI * getR() * getR();
}double Cylinder::findPerimeter() {return 2 * PI * getR() * 2;
}double sumArea(GeometricObject* a[], int n) {double sum = 0;for (int i = 0; i < n; i++) {sum += a[i]->findArea();}return sum;
}

GeoAreaSum.cpp

#include 
#include "GeometricObject.h"int main() {GeometricObject *objects[3];objects[0] = new Circle(5);objects[1] = new Cylinder(5, 10);objects[2] = new Rectangle(6, 8);cout << "总面积为:" << sumArea(objects, 3) << endl;return 0;
}

Java

GeometricObject.java

public abstract class GeometricObject {abstract double findArea();abstract double findPerimeter();
}

Circle.java

public class Circle extends GeometricObject{private double r;public Circle(double r) {this.r = r;}public double getR() {return r;}@Overridedouble findArea() {return Math.PI*r*r;}@Overridedouble findPerimeter() {return 2*Math.PI*r;}
}

Rectangle.java

public class Rectangle extends GeometricObject{private double w;private double h;public Rectangle(double w, double h) {this.w = w;this.h = h;}@Overridedouble findArea() {return w*h;}@Overridedouble findPerimeter() {return 2*(w+h);}
}

Cylinder.java

public class Cylinder extends Circle{private double h;public Cylinder(double h, double r) {super(r);this.h = h;}@Overridedouble findArea() {return 2*Math.PI*getR()*h+2*Math.PI*getR()*getR();}@Overridedouble findPerimeter() {return 2*Math.PI*getR()*2;}
}

GeoAreaSum.java

public class GeoAreaSum {public static double sumArea(GeometricObject[] a) {double sum = 0;for (GeometricObject geometricObject : a) {sum += geometricObject.findArea();}return sum;}public static void main(String[] args) {GeometricObject[] objects = new GeometricObject[3];objects[0] = new Circle(5);objects[1] = new Cylinder(5,10);objects[2] = new Rectangle(6,8);System.out.println("总面积为:" + sumArea(objects));}
}

参考资料

1. C++子类继承父类时如何写构造函数

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