杨其菊201771010134《面向对象程序设计（java)》第四周学习总结

《面向对象程序设计（java)》 第四周学习总结

第一部分：理论知识

1.类与对象

a.类（class）是构造对象的模板或蓝图。由类构造对象的过程称为创建类的实例；

java中类声明的格式如下：

[类修饰符] class 类名 [extends 父类名称] [implements 接口名称列表]

{

变量定义及初始化;

方法定义及方法体;

}

public：类的访问控制符。Java类具有两种访问访问修饰符：public和default。public允许类具有完全开放的可见性，所有其他类都可以访问它，省略public，则为default，即只有位于同一个包（本质上就是文件夹）中的类可以访问该类。

abstract指明该类为一个抽象类，说明该类是一个定义不完全的类，需要被继承，才能实例化创建对象。

b.对象：即数据，对象有三个特性——1.行为 2.状态 3.标识。

c、方法，变量.

d.类是对象，事物的描述和抽象，是具有相同属性和行为的对象集合。对象则是该类事物的实例。　　　　

2.预定义类　、API　

Math类、String类、math类、Scanner类、LocalDate类

3.自定义类

4.静态域和静态方法    绝大多数面向对象程序设计语言中，静态域被称为类域。如果将域定义为static，每个类中只有一个这样的域。而每个对象对于所有的实例域却都有自己的一份拷贝。

构造器、更改器方法、访问器方法，静态方法

5.方法参数

6.包

7.文档注释技术

第二部分：实验部分

1、实验目的与要求

(1) 理解用户自定义类的定义；

(2) 掌握对象的声明；

(3) 学会使用构造函数初始化对象；

(4) 使用类属性与方法的使用掌握使用；

(5) 掌握package和import语句的用途。

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。
     }
 }

测试结果截图如下：

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。

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

（1）源代码：

（2）Employee.java、 EmployeeTest.java 运行结果截图：

 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];

       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;
    }
 }

（3）EmployeeTest.java源代码及运行结果截图如下

 import java.time.LocalDate;
 import java.util.Scanner;
 /**
  * This program tests the Employee class.
  * @version 1.12 2018-09-25
  * @author yangxiaoxiao
  */
 public class StudentTest
 {
     String name;
     String sex;
     double score;
    public static void main(String[] args)
     //public static void ScannerTest(){
    {

        int i = 0;

         System.out.print("numer：");
         Scanner sc= new Scanner(System.in);
        int number = sc.nextInt();
        StudentTest Stu[] = new StudentTest[number];
         for (i = 0; i < Stu.length; i++) {
             Stu[i] = new StudentTest();
             System.out.print( (i + 1)+" "+"姓名:" );
             Stu[i].name = sc.next();
             System.out.print( (i + 1)+" " +"性别：");
             Stu[i].sex = sc.next();
             System.out.print( (i + 1)+" " +"java成绩：");
             Stu[i].score = sc.nextDouble();
         }

       System.out.println("\t姓名\t性别\t成绩");
         for (StudentTest StudentTest : Stu) {
             System.out.println("\t" + StudentTest.name+ "\t" + StudentTest.sex + "\t" + StudentTest.score);
         }

    }
 }

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；

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

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；

 /**
  * 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

l 编辑、编译、调试运行程序4-5（教材129）；

l 结合程序运行结果，理解程序代码，掌握Java用户自定义类的用法，掌握对象构造方法及对象使用方法，在相关代码后添加注释。

 import java.util.*;

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

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

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

 class Employee
 {
 private static int nextId;

 private int id;
 private String name = ""; // instance field initialization
 private double salary;

 // static initialization block
 static
 {
 Random generator = new Random();
 // set nextId to a random number between 0 and 9999
 nextId = generator.nextInt(10000);
 }

 // object initialization block
 {
 id = nextId;
 nextId++;
 }

 // three overloaded constructors
 public Employee(String n, double s)
 {
 name = n;
 salary = s;
 }

 public Employee(double s)
 {
 // calls the Employee(String, double) constructor
 this("Employee #" + nextId, s);
 }

 // the default constructor
 public Employee()
 {
 // name initialized to ""--see above
 // salary not explicitly set--initialized to 0
 // id initialized in initialization block
 }

 public String getName()
 {
 return name;
 }

 public double getSalary()
 {
 return salary;
 }

 public int getId()
 {
 return id;
 }
 }

测试程序5：

l 编辑、编译、调试运行程序4-6、4-7（教材135）；

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；

4-6

 import com.horstmann.corejava.*;
 // the Employee class is defined in that package

 import static java.lang.System.*;

 /**
  * This program demonstrates the use of packages.
  * @version 1.11 2004-02-19
  * @author Cay Horstmann
  */
 public class PackageTest
 {
    public static void main(String[] args)
    {
       // because of the import statement, we don't have to use
       // com.horstmann.corejava.Employee here
       Employee harry = new Employee("Harry Hacker", 50000, 1989, 10, 1);

       harry.raiseSalary(5);

       // because of the static import statement, we don't have to use System.out here
       out.println("name=" + harry.getName() + ",salary=" + harry.getSalary());
    }
 }

4-7

 package com.horstmann.corejava;

 // the classes in this file are part of this package

 import java.time.*;

 // import statements come after the package statement

 /**
  * @version 1.11 2015-05-08
  * @author Cay Horstmann
  */
 public class Employee
 {
    private String name;
    private double salary;
    private LocalDate hireDay;

    public Employee(String name, double salary, int year, int month, int day)
    {
       this.name = name;
       this.salary = salary;
       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;
    }
 }

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。

 import java.util.*;

 public class Com {

     public static void main(String[] args) {

         Scanner in = new Scanner(System.in);
         System.out.println("输入长:");
         double  length = in.nextDouble();
         System.out.println("输入宽:");
         double  width = in.nextDouble();
         System.out.println("输入半径:");
         double  radius = in.nextDouble();
         Rectangle a=new Rectangle(length,width);
         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);
     }

 }

 class Rectangle {
     private double width;
     private double length;
     public Rectangle(double w,double l)
     {
         width=w;
         length=l;
     }
     public double getPerimeter()
     {
         double Perimeter = (width+length)*2;
         return Perimeter;
     }
     public double getArea()
     {
         double Area = width*length;
         return Area;
     }
 }

 class Circle {

     private double radius;
     double PI = 3.14;
     public Circle(double r)
     {
         radius=r;
     }
     public double getPerimeter()
     {
         double Perimeter = 2*PI*radius;
         return Perimeter;
     }
     public double getArea()
     {
         double Area = PI*radius*radius;
         return Area;
     }
 }

第三部分：实验总结

通过这个周的学习，学习了面向对象程序设计的一些基础知识，类、对象、对象的三个特征（行为、状态和标识），明确了创建类、构造和初始化对象的格式、以及熟悉预定义类API的使用。学学习了一些常用的类：Math类、String类、Scanner类、LocalDate类等。在课上课下的阅读程序中，以及编写程序时，有些疑惑，不清楚代码语句的作用和和如何去编写代码，看懂不等于会！