201771010106东文财《面向对象程序设计(java)》第四章学习总结
实验四类与对象的定义及使用
实验时间 2018-9-20
第一部分:理论知识学习部分
1.类
类(class)是具有相同属性和行为的一组对象的集合,是构造程序的基本单元,是构造对象的模板或蓝图。
2.对象
对象:即数据,对象有三个特性——1.行为 2.状态 3.标识。
3.类与对象的关系
(1)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)类是一个静态的概念,类本身不携带任何数据。当没有为类创建任何对象时,类本身不存在于内存空间中。对象是一个动态的概念。每一个对象都存在着有别于其它对象的属于自己的独特的属性和行为。对象的属性可以随着它自己的行为而发生改变。
4.识别类
a.实例域:可将实例域定义为final,构建对象时必须初始化这样的域。
b.静态域: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。
c.静态方法:静态方法是一种不能向对象实时操作的方法。可以使用对象调用静态方法。
d.构造器方法:构造器与类同名。构造器总是伴随着new操作符的执行被调用,而不能对一个已经存在的对象调用构造器来达到重新设置实例域的目的。
e.更改器方法:调用更改器方法后对象的状态会改变。
f.访问器方法:只访问对象而不修改对象的方法。
g.main方法:main方法不对任何对象进行操作。静态的main方法将执行并创建程序所需要的对象。
7、重载
多个方法有相同的名字、不同的参数、便产生了重载。Java允许重载任何方法,而不只是构造器方法
8、Java允许使用包将类组织起来。借助包可以方便地组织自己的代码,并将自己的代码与别人提供的代码库分开管理。而且使用包可以确保类名的唯一性。
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。 } } |
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程序如下:
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) { // 用三个Employee对象填充staff数组 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); //将每个人的工资提高5% for (Employee e : staff) e.raiseSalary(5); //打印出员工反对的信息 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; } }
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
package StudentTest;
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;
}
}
}
}
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。
package nisf; /** * 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 tt; /** * 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:
编辑、编译、调试运行程序4-5(教材129);
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。
package tt; 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:
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;
package te; import static java.lang.System.*; /** * This program demonstrates the use of packages. * @version 1.11 2004-02-19 * @author Cay Horstmann */ public class tt { 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()); } }
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。
代码如下:
package hh; import java.util.Scanner; public class jj { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.println("长方形长与宽:"); int length = in.nextInt(); int width = in.nextInt(); Rectangle a = new Rectangle(length, width); System.out.println("周长:" + a.getPerimeter()); System.out.println("面积:" + a.getArea()); System.out.println("输入圆半径:"); int r = in.nextInt(); Circle b = new Circle(r); System.out.println("周长为:" + b.getPerimeter()); System.out.println("面积为:" + b.getArea()); System.out.println("长方形和圆的周长之和=" + (a.getPerimeter() + b.getPerimeter())); System.out.println("长方形和圆的面积之和=" + (a.getArea() + b.getArea())); } } class Rectangle { private int length; private int width; public Rectangle(int l, int w) { length = l; width = w; } public int getPerimeter() { int Perimeter = (length + width) * 2; return Perimeter; } public int getArea() { int Area = length * width; return Area; } } class Circle { private int radius; double Pi = 3.14; public Circle(int r) { radius = r; } public double getPerimeter() { double Perimeter = 2 * Pi * radius; return Perimeter; } public double getArea() { double Area = Pi * radius * radius; return Area; } }
实验结果:
实验总结:
通过本次实验我更加了解了本章的知识,尤其是对输入输出有了一定的强化,此次实验我主要是对一些程序进行了分析,从中我学到了很多知识,我相信我会在以后的编程过程中运用到现在我学习到的知识。还有本次实验我有很大不足,下次我会努力更正。