徐思201771010132《面向对象程序设计（java）》第四周学习总结

一、理论知识部分

类是构建造对象的模板和蓝图。类是对一组具有相同属性、行为、关系及语义的对象的描述,是具有相同类型对象的抽象。类中使用变量来表示对象的抽象状态,用方法抽象出对象的行为特征。

封装是将数据和行为组合在一个包内，并对对象的使用者隐藏了数据的实现方法。对象中的数据称为实例域，操作数据的过程称为方法，对于每个特定的类对象都有一组特定的实例域值，这些值的集合就是这个对象地当前状态。

对象的三个主要特性：对象的行为、对象的状态、对象标识。

标准类（预定义类）：Math类，math类（大整数，大浮点数），string类，scanner类。

构造器是一种特殊的方法，用来构造并初始化对象。构造器名字应与类名相同；要想构造一个Data对象，需要在构造器前面加上new操作符。

更改器方法：改变对象的状态，前缀为set。

访问器方法：只访问对象不修改对象的方法。前缀为get。

二、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

 1 package test0;
 2 
 3 import java.io.*;
 4 import java.util.Scanner;
 5 
 6 public class FileWriteReadTest {
 7 
 8     public static void main(String[] args) throws IOException{
 9         // TODO Auto-generated method stub
10         PrintWriter out = new PrintWriter("myfile.txt");
11         out.println("姓名 高数 Java 数据结构 平均成绩 总成绩");
12         out.println("张三 20 30 40 0 0");
13         out.println("李四 50 60 70 0 0");
14         out.close();//输出完毕，需要close
15         //读入文件演示
16         Scanner in = new Scanner(new File("myfile.txt"));//为myfile.txt这个File创建一个扫描器in
17         int number = 1;//行号
18         System.out.println(in.nextLine());
19         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
20             String line = in.nextLine();//读出myfile.txt的下一行
21             System.out.print("第"+(++number)+"行的内容: ");            
22             var linescanner = new Scanner(line);//行内容建立扫描器
23             linescanner.useDelimiter(" ");//使用空格作为分隔符
24             String name = linescanner.next();
25             String math = linescanner.next();
26             String java = linescanner.next();
27             String ds = linescanner.next();
28             String avg = linescanner.next();
29             String total = linescanner.next();
30             System.out.println("name="+name+"  math="+math+"  java="+java+"  ds="+ds+"  avg="+avg+"  total="+total);
31         }
32         in.close();//读入完毕，最后需要对其进行close。
33     }    
34 
35 }

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；

package test0;

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;
}
}

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 package test05;
 2 
 3 import java.util.*;
 4 
 5 public class Student {
 6 
 7     public static void main(String[] args) {
 8         // TODO 自动生成的方法存根
 9          int x=2;
10           Employee[] staff = new Employee[x];
11           System.out.println("请输入学生：");
12           Scanner in = new Scanner(System.in); 
13           for(int i=0;i<staff.length;i++) {
14               staff[i]=new Employee(in.next(),in.next(),in.nextInt());
15           }
16           System.out.println("name"+" "+"sex"+" "+" "+"javascore");
17 
18           // 输出二个学生的信息
19           for (Employee e : staff)
20              System.out.println(e.getName() +"   "+e.getSex()+"        "+e.getJavaScore());
21        }
22     }
23 
24     class Employee
25     {
26        private String name;
27        private String sex;
28        private int javascore;
29        public Employee(String n, String s, int m)
30        {
31           name = n;
32           sex = s;
33           javascore =m;
34        }
35 
36        public String getName()
37        {
38           return name;
39        }
40 
41        public String getSex()
42        {
43           return sex;
44        }
45 
46        public int getJavaScore()
47        {
48           return javascore;
49        }
50     }

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。

 1 package test01;
 2 
 3 /**
 4  * This program demonstrates static methods.
 5  * @version 1.01 2004-02-19
 6  * @author Bay Horstmann
 7  */
 8 public class StaticTest
 9 {
10    public static void main(String[] args)
11    {
12       // fill the staff array with three Employee objects
13       Employee[] staff = new Employee[3];
14 
15       staff[0] = new Employee("Tom", 40000);
16       staff[1] = new Employee("Dick", 60000);
17       staff[2] = new Employee("Harry", 65000);
18 
19       // print out information about all Employee objects
20       for (Employee e : staff)
21       {
22          e.setId();
23          System.out.println("name=" + e.getName() + ",id=" + e.getId() + ",salary="
24                + e.getSalary());
25       }
26 
27       int n = Employee.getNextId(); // calls static method
28       System.out.println("Next available id=" + n);
29    }
30 }
31 
32 class Employee
33 {
34    private static int nextId = 1;
35 
36    private String name;
37    private double salary;
38    private int id;
39 
40    public Employee(String n, double s)
41    {
42       name = n;
43       salary = s;
44       id = 0;
45    }
46 
47    public String getName()
48    {
49       return name;
50    }
51 
52    public double getSalary()
53    {
54       return salary;
55    }
56 
57    public int getId()
58    {
59       return id;
60    }
61 
62    public void setId()
63    {
64       id = nextId; // set id to next available id
65       nextId++;
66    }
67 
68    public static int getNextId()
69    {
70       return nextId; // returns static field
71    }
72 
73    public static void main(String[] args) // unit test
74    {
75       Employee e = new Employee("Harry", 50000);
76       System.out.println(e.getName() + " " + e.getSalary());
77    }
78 }

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 test03;

/**
 * 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4：

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。

 1 package test02;
 2 
 3 import java.util.*;
 4 
 5 /**
 6  * This program demonstrates object construction.
 7  * @version 1.01 2004-02-19
 8  * @author Cay Horstmann
 9  */
10 public class ConstructorTest
11 {
12    public static void main(String[] args)
13    {
14       // fill the staff array with three Employee objects
15       Employee[] staff = new Employee[3];
16 
17       staff[0] = new Employee("Harry", 40000);
18       staff[1] = new Employee(60000);
19       staff[2] = new Employee();
20 
21       // print out information about all Employee objects
22       for (Employee e : staff)
23          System.out.println("name=" + e.getName() + ",id=" + e.getId() + ",salary="
24                + e.getSalary());
25    }
26 }
27 
28 class Employee
29 {
30    private static int nextId;
31 
32    private int id;
33    private String name = ""; // instance field initialization
34    private double salary;
35   
36    // static initialization block
37    static
38    {
39       Random generator = new Random();
40       // set nextId to a random number between 0 and 9999
41       nextId = generator.nextInt(10000);
42    }
43 
44    // object initialization block
45    {
46       id = nextId;
47       nextId++;
48    }
49 
50    // three overloaded constructors
51    public Employee(String n, double s)
52    {
53       name = n;
54       salary = s;
55    }
56 
57    public Employee(double s)
58    {
59       // calls the Employee(String, double) constructor
60       this("Employee #" + nextId, s);
61    }
62 
63    // the default constructor
64    public Employee()
65    {
66       // name initialized to ""--see above
67       // salary not explicitly set--initialized to 0
68       // id initialized in initialization block
69    }
70 
71    public String getName()
72    {
73       return name;
74    }
75 
76    public double getSalary()
77    {
78       return salary;
79    }
80 
81    public int getId()
82    {
83       return id;
84    }
85 }

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；

 1 package test03;
 2 
 3 import static java.lang.System.out;
 4 
 5 import com.horstmann.corejava.Employee;
 6 
 7 /**
 8  * This program demonstrates the use of packages.
 9  * @version 1.11 2004-02-19
10  * @author Cay Horstmann
11  */
12 public class PackageTest
13 {
14    public static void main(String[] args)
15    {
16       // because of the import statement, we don't have to use 
17       // com.horstmann.corejava.Employee here
18       Employee harry = new Employee("Harry Hacker", 50000, 1989, 10, 1);
19 
20       harry.raiseSalary(5);
21 
22       // because of the static import statement, we don't have to use System.out here
23       out.println("name=" + harry.getName() + ",salary=" + harry.getSalary());
24    }
25 }

 1 package com.horstmann.corejava;
 2 
 3 // the classes in this file are part of this package
 4 
 5 import java.time.*;
 6 
 7 // import statements come after the package statement
 8 
 9 /**
10  * @version 1.11 2015-05-08
11  * @author Cay Horstmann
12  */
13 public class Employee
14 {
15    private String name;
16    private double salary;
17    private LocalDate hireDay;
18 
19    public Employee(String name, double salary, int year, int month, int day)
20    {
21       this.name = name;
22       this.salary = salary;
23       hireDay = LocalDate.of(year, month, day);
24    }
25 
26    public String getName()
27    {
28       return name;
29    }
30 
31    public double getSalary()
32    {
33       return salary;
34    }
35 
36    public LocalDate getHireDay()
37    {
38       return hireDay;
39    }
40 
41    public void raiseSalary(double byPercent)
42    {
43       double raise = salary * byPercent / 100;
44       salary += raise;
45    }
46 }

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；

将两个对象的周长加总输出，将两个对象的面积加总输出。

 1 package test05;
 2 
 3 import java.util.Scanner;
 4 
 5 public class add {
 6 
 7     public static void main(String[] args) {
 8         // TODO 自动生成的方法存根
 9         Scanner in=new Scanner(System.in);
10         System.out.println("请输入长方形的长与宽：");
11         int length=in.nextInt();
12         int width=in.nextInt();
13         Rectangle  a=new Rectangle(length, width);
14         System.out.println("长方形的周长为："+a.getPerimeter());
15         System.out.println("长方形的面积为："+a.getArea());
16         System.out.println("请输入圆的半径：");
17         int r=in.nextInt();
18         Circle b=new Circle(r);
19         System.out.println("圆的周长为："+b.getPerimeter());
20         System.out.println("圆的面积为："+b.getArea());
21         System.out.println("长方形和圆的周长之和="+(a.getPerimeter()+b.getPerimeter()));
22         System.out.println("长方形和圆的面积和="+(a.getArea()+b.getArea()));
23     }
24 }
25 class Rectangle
26 {
27     private int length;
28     private int width;
29     public Rectangle(int l,int w)
30     {
31         length=l;
32         width=w;
33     }
34     public int getPerimeter()
35     {
36         int Perimeter=(length+width)*2;
37         return Perimeter;
38     }
39     
40     public int getArea()
41     {
42         int Area=length*width;
43         return Area;
44     }
45 }
46 class Circle
47 {
48     private int radius;
49     double Pi=3.14;
50     public Circle(int r)
51     {
52         radius=r;
53     }
54     public double getPerimeter()
55     {
56         double Perimeter=2*Pi*radius;
57         return Perimeter;
58     }
59     public double getArea()
60     {
61         double Area=Pi*radius*radius;
62         return Area;
63     }
64
65 }

实验总结：通过上机实验，更好的将课本知识运用到实践中，有利于更好的掌握了解Java知识。通过这次实验，我了解到了什么是类，对象。但是对于上机实验仍不是很熟悉，缺少练习，学习Java的关键是要坚持练习，慢慢地了解代码的内容，课后多做练习，多上机做实验，熟能生巧。通过多次练习，查漏补缺，加强对代码的编程。

posted @ 2018-09-26 00:33 徐思阅读(113) 评论(0) 编辑收藏举报

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徐思

徐思201771010132《面向对象程序设计（java）》第四周学习总结

实验3

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