《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！