第四周java实验

实验四 类与对象的定义及使用

实验时间 2018-9-20

1、实验目的与要求

(1) 理解用户自定义类的定义；

类是具有相同属性和行为的一组对象的集合。java中，用构造器构造并初始化对象。

类是构造对象的基本单元。

构造器是类中一个特殊的方法，其方法名与类名相同。

(2) 掌握对象的声明；

对象是客观事物的抽象，类是对对象的抽象。类是一种抽象的数据类型，其定义为：class 类名{ } 他们的关系是对象是类的实例，类是对象的模板。

对象的声明：

类名  对象名 = new 类名（）；

对象的调用

访问属性：对象名.属性名；

访问方法：对象名.方法名；

(3) 学会使用构造函数初始化对象；

构造函数的特点：构造函数名与类名相同；构造函数不返回任何值，也没有返回类型；每一类可以有零个或多个构造方法；构造方法在创建对象时自动执行，一般不用显示的直接调用。

2、实验内容和步骤

实验1 测试以下程序，掌握文件输入输出程序设计技术（文件输入输出，教材61-62）.

import java.io.*;
import java.util.*;
public class FileWriteReadTest {
    public static void main(String[] args) throws IOException{
        //写入文件演示
        PrintWriter out = new PrintWriter("myfile.txt");
        out.println("姓名 高数 Java 数据结构 平均成绩 总成绩");
        out.println("张三 20 30 40 0 0");
        out.println("李四 50 60 70 0 0");
        out.close();//输出完毕，需要close
        //读入文件演示
        Scanner in = new Scanner(new File("myfile.txt"));//为myfile.txt这个File创建一个扫描器in
        int number = 1;//行号
        System.out.println(in.nextLine());
        while(in.hasNextLine()){//判断扫描器是否还有下一行未读取，该循环把文件的每一行都读出
            String line = in.nextLine();//读出myfile.txt的下一行
            System.out.print("第"+(++number)+"行的内容: ");
            Scanner linescanner = new Scanner(line);//行内容建立扫描器
            linescanner.useDelimiter(" ");//使用空格作为分隔符
            String name = linescanner.next();
            String math = linescanner.next();
            String java = linescanner.next();
            String ds = linescanner.next();
            String avg = linescanner.next();
            String total = linescanner.next();
            System.out.println("name="+name+"  math="+math+"  java="+java+"  ds="+ds+"  avg"+avg+"  total="+total);
        }
        in.close();//读入完毕，最后需要对其进行close。
    }
}

实验2 导入第4章示例程序并测试。

测试程序1：

l 编辑、编译、调试运行程序4-2（教材104页）；

l 结合程序运行结果，掌握类的定义与类对象的用法，并在程序代码中添加类与对象知识应用的注释；

l 尝试在项目中编辑两个类文件（Employee.java、 EmployeeTest.java ），编译并运行程序。

import java.time.*;

/**
 * This program tests the Employee class.
 * @version 1.12 2015-05-08
 * @author Cay Horstmann
 */
public class EmployeeTest
{
   public static void main(String[] args)
   {
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[3];

    //构造一个数组,并填入如三个雇员对象。
      staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);
      staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
      staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);

      // raise everyone's salary by 5%
      for (Employee e : staff)
         e.raiseSalary(5);

      // print out information about all Employee objects
      for (Employee e : staff)
         System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
               + e.getHireDay());
   }
}

class Employee
{
   private String name;
   private double salary;
   private LocalDate hireDay;

   public Employee(String n, double s, int year, int month, int day)
   {
      name = n;
      salary = s;
      hireDay = LocalDate.of(year, month, day);
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public LocalDate getHireDay()
   {
      return hireDay;
   }

   public void raiseSalary(double byPercent)
   {
      double raise = salary * byPercent / 100;
      salary += raise;

   }
}

l 参考教材104页EmployeeTest.java，设计StudentTest.java，定义Student类，包含name（姓名）、sex（性别）、javascore（java成绩）三个字段，编写程序，从键盘输入学生人数，输入学生信息，并按以下表头输出学生信息表：

姓名      性别   java成绩

import java.util.ArrayList;
import java.util.Scanner;
public class StudentTest{

private int number;
private String name;
private String sex;
private int score;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public int getScore() {
return number;
}
public void setScore(int score) {
this.number = number;
}
public StudentTest(){}

public StudentTest(int number, String name) {
this.number = number;
this.name = name;
this.sex = sex;
}

public StudentTest writeInfo(){
    StudentTest st = new StudentTest();
Scanner in = new Scanner(System.in);
System.out.println("请输入学生的学号:");
number = in.nextInt();
st.setNumber(number);
System.out.println("请输入学生的姓名:");
String name = in.next();
st.setName(name);
System.out.println("请输入学生的性别:");
String sex = in.next();
st.setSex(sex);
System.out.println("请输入学生的Java成绩:");
score = in.nextInt();
st.setNumber(score);
return st;
}

public void readInfo(ArrayList list){

for(int i=0;i<=list.size()-1;i++){
    StudentTest st = new StudentTest();
st = (StudentTest) list.get(i);
System.out.println("第"+(i+1)+"位学生的学号:" + st.getNumber());
System.out.println("第"+(i+1)+"位学生的姓名:" + st.getName());
System.out.println("第"+(i+1)+"位学生的性别:" + st.getSex());
System.out.println("第"+(i+1)+"位学生的成绩:" + st.getScore());
}
}

public static void main(String[]args){ ArrayList<StudentTest> list = new ArrayList<StudentTest>();
StudentTest st = new StudentTest();
Scanner in = new Scanner(System.in);
while(true){
System.out.println("1、输入学生信息");
System.out.println("2、输出学生信息");
System.out.println("请选择:");

int option = in.nextInt();

switch (option) {
case 1:
list.add(st.writeInfo());
break;
case 2:
st.readInfo(list);
break;
default:
break;
}
}
}
}

程序运行结果为：

测试程序2：

l 编辑、编译、调试运行程序4-3（教材116）；

l 结合程序运行结果，理解程序代码，掌握静态域（netxtId）与静态方法（getNextId）的用法，在相关代码后添加注释；

l 理解Java单元（类）测试的技巧。

/**
 * This program demonstrates static methods.
 * @version 1.01 2004-02-19
 * @author Cay Horstmann
 */
public class StaticTest
{
   public static void main(String[] args)
   {
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[3];

      staff[0] = new Employee("Tom", 40000);
      staff[1] = new Employee("Dick", 60000);
      staff[2] = new Employee("Harry", 65000);

      // print out information about all Employee objects
      for (Employee e : staff)
      {
         e.setId();
         System.out.println("name=" + e.getName() + ",id=" + e.getId() + ",salary="
               + e.getSalary());
      }

      int n = Employee.getNextId(); // calls static method
      System.out.println("Next available id=" + n);
   }
}

class Employee
{
   private static int nextId = 1;

   private String name;
   private double salary;
   private int id;

   public Employee(String n, double s)
   {
      name = n;
      salary = s;
      id = 0;
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public int getId()
   {
      return id;
   }

   public void setId()
   {
      id = nextId; // set id to next available id
      nextId++;
   }

   public static int getNextId()
   {
      return nextId; // returns static field
   }

   public static void main(String[] args) // unit test
   {
      Employee e = new Employee("Harry", 50000);
      System.out.println(e.getName() + " " + e.getSalary());
   }
}

测试程序3：

l 编辑、编译、调试运行程序4-4（教材121）；

l 结合程序运行结果，理解程序代码，掌握掌握Java方法参数的用法，在相关代码后添加注释；

package 小陈1;

/**
* This program demonstrates parameter passing in Java.
* @version 1.00 2000-01-27
* @author Cay Horstmann
*/
public class ParamTest
{
public static void main(String[] args)
{
/*
* Test 1: Methods can't modify numeric parameters
*/
System.out.println("Testing tripleValue:");
double percent = 10;
System.out.println("Before: percent=" + percent);
tripleValue(percent);
System.out.println("After: percent=" + percent);

/*
* Test 2: Methods can change the state of object parameters
*/
System.out.println("\nTesting tripleSalary:");
Employee harry = new Employee("Harry", 50000);
System.out.println("Before: salary=" + harry.getSalary());
tripleSalary(harry);
System.out.println("After: salary=" + harry.getSalary());

/*
* Test 3: Methods can't attach new objects to object parameters
*/
System.out.println("\nTesting swap:");
Employee a = new Employee("Alice", 70000);
Employee b = new Employee("Bob", 60000);
System.out.println("Before: a=" + a.getName());
System.out.println("Before: b=" + b.getName());
swap(a, b);
System.out.println("After: a=" + a.getName());
System.out.println("After: b=" + b.getName());
}

public static void tripleValue(double x) // doesn't work
{
x = 3 * x;
System.out.println("End of method: x=" + x);
}

public static void tripleSalary(Employee x) // works
{
x.raiseSalary(200);
System.out.println("End of method: salary=" + x.getSalary());
}

public static void swap(Employee x, Employee y)
{
Employee temp = x;
x = y;
y = temp;
System.out.println("End of method: x=" + x.getName());
System.out.println("End of method: y=" + y.getName());
}
}

class Employee // simplified Employee class
{
private String name;
private double salary;

public Employee(String n, double s)
{
name = n;
salary = s;
}

public String getName()
{
return name;
}

public double getSalary()
{
return salary;
}

public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
}

测试程序5：

l 编辑、编译、调试运行程序4-6、4-7（教材135）；

l 结合程序运行结果，理解程序代码，掌握Java包的定义及用法，在相关代码后添加注释；

import java.time.*;

/**
 * This program tests the Employee class.
 * @version 1.12 2015-05-08
 * @author Cay Horstmann
 */
public class EmployeeTest
{
   public static void main(String[] args)
   {
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[];

      staff[] = new Employee("Carl Cracker", , , , );
      staff[] = new Employee("Harry Hacker", , , , );
      staff[] = new Employee("Tony Tester", , , , );

      // raise everyone's salary by 5%
      for (Employee e : staff)
         e.raiseSalary();

      // print out information about all Employee objects
      for (Employee e : staff)
         System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
               + e.getHireDay());
   }
}

class Employee
{
   private String name;
   private double salary;
   private LocalDate hireDay;

   public Employee(String n, double s, int year, int month, int day)
   {
      name = n;
      salary = s;
      hireDay = LocalDate.of(year, month, day);
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public LocalDate getHireDay()
   {
      return hireDay;
   }

   public void raiseSalary(double byPercent)
   {
      double raise = salary * byPercent / ;
      salary += raise;
   }
}

实验3  编写长方形类Rectangle与圆形类Circle，其中Rectangle类设置私有属性：width,length；Circle类设置私有属性radius。编写Rectangle类的带参构造函数Rectangle(int width,int length), Circle类的带参构造函数Circle(int radius)，编写两个类的toString方法(Eclipse可自动生成)。上述2个类均定义以下方法：

求周长的方法public int getPerimeter()

求面积的方法public int getArea()

在main方法中完成以下任务：

（1） 输入1行长与宽，创建一个Rectangle对象；

（2） 输入1行半径，创建一个Circle对象；

（3） 将两个对象的周长加总输出，将两个对象的面积加总输出。

package 小陈4;
import java.util.*;

 public class Rectangle{
     public static void main(String[] args) {
         Scanner in = new Scanner(System.in);
         System.out.println("请输入长:");
         double  length = in.nextDouble();
         System.out.println("请输入宽:");
         double  width = in.nextDouble();
         System.out.println("请输入半径:");
         double  radius = in.nextDouble();
         Rectangle a=new Rectangle();
         Circle    b=new Circle(radius);
         System.out.println("矩形周长："+a.getPerimeter()+"矩形面积："+a.getArea());
         System.out.println("圆周长"+b.getPerimeter()+"圆面积："+b.getArea());
         double x = a.getPerimeter()+b.getPerimeter();
         double  y = a.getArea()+b.getArea();
         System.out.println("周长和："+x+"面积和："+y);
     }

    private double getArea() {
        // TODO Auto-generated method stub
        return ;
    }

    private double getPerimeter() {
        // TODO Auto-generated method stub
        return ;
    }
  }

 class Rectangle1 {
     private double width;
     private double length;
     public Rectangle1(double w,double l)
     {
         width=w;
         length=l;
     }
     public double getPerimeter()
     {
        double Perimeter = (width+length)*;
        return Perimeter;
     }
     public double getArea()
     {
         double Area = width*length;
         return Area;
     }
 }
 class Circle {

     private double R;
     double PI = 3.14;
     public Circle(double r)
     {
         R=r;
     }
     public double getPerimeter()
     {
         double Perimeter = *PI*R;
         return Perimeter;
     }
     public double getArea()
     {
         double Area = PI*R*R;
         return Area;
     }
 }