201871010128杨丽霞《面向对象程序设计（java）》第七周学习总

201871010128-杨丽霞-《面向对象程序设计（java）》第七周学习总结

项目	内容
这个作业属于哪个课程	https://www.cnblogs.com/nwnu-daizh/
这个作业的要求在哪里	https://www.cnblogs.com/nwnu-daizh/p/11654436.html
作业学习目标	掌握四种访问权限修饰符的使用特点； 掌握Object类的用途及常用API； 掌握ArrayList类的定义方法及用途； 掌握枚举类定义方法及用途； 结合本章实验内容，理解继承与多态性两个面向对象程序设计特征，并体会其优点。

 

1、实验目的与要求

（1） 掌握四种访问权限修饰符的使用特点；

（2）掌握Object类的用途及常用API；

（3）掌握ArrayList类的定义方法及用法；

（4）掌握枚举类定义方法及用途；

（5）结合本章实验内容，理解继承与多态性两个面向对象程序设计特征，并体会其优点。

2、实验内容和步骤

实验1：在“System.out.println(...);”语句处按注释要求设计代码替换...，观察代码录入中IDE提示，以验证四种权限修饰符的用法。（20分）

实验代码如下：

class Parent {
    private String p1 = "这是Parent的私有属性";
    public String p2 = "这是Parent的公有属性";
    protected String p3 = "这是Parent受保护的属性";
    String p4 = "这是Parent的默认属性";
    private void pMethod1() {
        System.out.println("我是Parent用private修饰符修饰的方法");
    }
    public void pMethod2() {
        System.out.println("我是Parent用public修饰符修饰的方法");
    }
    protected void pMethod3() {
        System.out.println("我是Parent用protected修饰符修饰的方法");
    }
    void pMethod4() {
        System.out.println("我是Parent无修饰符修饰的方法");
    }
}
class Son extends Parent{
    private String s1 = "这是Son的私有属性";
    public String s2 = "这是Son的公有属性";
    protected String s3 = "这是Son受保护的属性";
    String s4 = "这是Son的默认属性";
    public void sMethod1() {
        System.out.println(...);//分别尝试显示Parent类的p1、p2、p3、p4值
        System.out.println("我是Son用public修饰符修饰的方法");
    }
    private void sMethod2() {
        System.out.println("我是Son用private修饰符修饰的方法");
    }
    protected void sMethod() {
        System.out.println("我是Son用protected修饰符修饰的方法");
    }
    void sMethod4() {
        System.out.println("我是Son无修饰符修饰的方法");
    }    
}
public class Demo {
    public static void main(String[] args) {
        Parent parent=new Parent();
        Son son=new Son();
        System.out.println(...);    //分别尝试用parent调用Paren类的方法、用son调用Son类的方法    
    }
}

运行结果如下：

 

 

 四种权限修饰符分别为：

public protected (default) private

其中(default)并不是关键字,是什么都不写的情况

权限大小：public>protected>(default)>private

它们在以下四种情况下的具体权限表现为：

 

实验2：导入第5章以下示例程序，测试并进行代码注释。

测试程序1

运行教材程序5-8、5-9、5-10，结合程序运行结果理解程序（教材174页-177页）；

删除程序中Employee类、Manager类中的equals()、hasCode()、toString()方法，背录删除方法，在代码录入中理解类中重写Object父类方法的技术要点。（15分）

程序5-8：

package equals;

/**
 * This program demonstrates the equals method.
 * @version 1.12 2012-01-26
 * @author Cay Horstmann
 */
public class EqualsTest
{
   public static void main(String[] args)
   {
      var alice1 = new Employee("Alice Adams", 75000, 1987, 12, 15);
      var alice2 = alice1;
      var alice3 = new Employee("Alice Adams", 75000, 1987, 12, 15);
      var bob = new Employee("Bob Brandson", 50000, 1989, 10, 1);

      System.out.println("alice1 == alice2: " + (alice1 == alice2));

      System.out.println("alice1 == alice3: " + (alice1 == alice3));

      System.out.println("alice1.equals(alice3): " + alice1.equals(alice3));

      System.out.println("alice1.equals(bob): " + alice1.equals(bob));

      System.out.println("bob.toString(): " + bob);

      var carl = new Manager("Carl Cracker", 80000, 1987, 12, 15);
      var boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
      boss.setBonus(5000);
      System.out.println("boss.toString(): " + boss);
      System.out.println("carl.equals(boss): " + carl.equals(boss));
      System.out.println("alice1.hashCode(): " + alice1.hashCode());
      System.out.println("alice3.hashCode(): " + alice3.hashCode());
      System.out.println("bob.hashCode(): " + bob.hashCode());
      System.out.println("carl.hashCode(): " + carl.hashCode());
   }
}

程序5-9：

package equals;

import java.time.*;
import java.util.Objects;

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;
   }

   public boolean equals(Object otherObject)
   {
      // a quick test to see if the objects are identical
      if (this == otherObject) return true;

      // must return false if the explicit parameter is null
      if (otherObject == null) return false;

      // if the classes don't match, they can't be equal
      if (getClass() != otherObject.getClass()) return false;

      // now we know otherObject is a non-null Employee
      var other = (Employee) otherObject;

      // test whether the fields have identical values
      return Objects.equals(name, other.name) 
         && salary == other.salary && Objects.equals(hireDay, other.hireDay);
   }

   public int hashCode()
   {
      return Objects.hash(name, salary, hireDay); 
   }

   public String toString()
   {
      return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay=" 
         + hireDay + "]";
   }
}

程序5-10：

package equals;

public class Manager extends Employee
{
   private double bonus;

   public Manager(String name, double salary, int year, int month, int day)
   {
      super(name, salary, year, month, day);
      bonus = 0;
   }

   public double getSalary()
   {
      double baseSalary = super.getSalary();
      return baseSalary + bonus;
   }

   public void setBonus(double bonus)
   {
      this.bonus = bonus;
   }

   public boolean equals(Object otherObject)
   {
      if (!super.equals(otherObject)) return false;
      var other = (Manager) otherObject;
      // super.equals checked that this and other belong to the same class
      return bonus == other.bonus;
   }

   public int hashCode()
   {
      return java.util.Objects.hash(super.hashCode(), bonus);
   }

   public String toString()
   {
      return super.toString() + "[bonus=" + bonus + "]";
   }
}

运行结果如下：

 删除程序中Employee类、Manager类中的equals()、hasCode()、toString()方法，背录删除方法后的代码：

Employee类

package equals;

import java.time.*;
import java.util.Objects;

public class Employee
{
   private String name;    //实例域定义
   private double salary;
   private LocalDate hireDay;

   public Employee(String name, double salary, int year, int month, int day)//构造器定义
   {
      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;
}


@Override
public boolean equals(Object otherObject) {
    // TODO Auto-generated method stub
    if(this==otherObject) return true;
    if(this==null) return false;
    if(getClass() != otherObject.getClass()) return false;
    Employee other=(Employee)otherObject;
    return Objects.equals(name,other.name)&&salary == other.salary&&Objects.equals(hireDay,other.hireDay);
}
@Override
public int hashCode() {
    // TODO Auto-generated method stub
    return Objects.hash(name,salary,hireDay);
}

@Override
public String toString() {
    // TODO Auto-generated method stub
    return getClass().getName()+"[name="+name+",salary="+salary+",hireday="+hireDay+"]";
}
  

}

 

Manager类

package equals;

public class Manager extends Employee
{
    private double bonus;
    public Manager(String name, double salary, int year, int month, int day) {
        super(name, salary, year, month, day);
        // TODO Auto-generated constructor stub
         bonus = 0;
    }
    public void setBonus(double bonus) {
        this.bonus = bonus;
    }
    @Override
    public double getSalary() {
        // TODO Auto-generated method stub
        double baseSalary= super.getSalary();
        return baseSalary+bonus;
    }
    @Override
    public boolean equals(Object otherObject) {
        // TODO Auto-generated method stub
        if(!super.equals(otherObject)) return false;
        Manager other=(Manager)otherObject;
        return bonus==other.bonus;
    }
    @Override
    public int hashCode() {
        // TODO Auto-generated method stub
        return super.hashCode()+17*new Double(bonus).hashCode();
    }
    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return super.toString()+"[bonus="+bonus+"]";
    }
 
}

 

运行结果：

测试程序2

l 在elipse IDE中调试运行程序5-11（教材182页），结合程序运行结果理解程序；

l 掌握ArrayList类的定义及用法；

l 在程序中相关代码处添加新知识的注释；

l 设计适当的代码，测试ArrayList类的set()、get()、remove()、size()等方法的用法。

程序5-11：

package arrayList;

import java.util.*;

/**
 * This program demonstrates the ArrayList class.
 * @version 1.11 2012-01-26
 * @author Cay Horstmann
 */
public class ArrayListTest
{
   public static void main(String[] args)
   {
      // fill the staff array list with three Employee objects
      var staff = new ArrayList<Employee>();

      staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));
      staff.add(new Employee("Harry Hacker", 50000, 1989, 10, 1));
      staff.add(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());
   }
}

package arrayList;

import java.time.*;

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;
   }
}

 

运行结果：

设计适当的代码，测试ArrayList类的set()、get()、remove()、size()等方法的用法

代码如下：

ackage arrayList;
 
import java.util.*;
 
/**
 * This program demonstrates the ArrayList class.
 * @version 1.11 2012-01-26
 * @author Cay Horstmann
 */
public class ArrayListTest
{
   private static final Employee element = null;
   private static final int index = 0;
 
   public static void main(String[] args)
   {
      // fill the staff array list with three Employee objects
      ArrayList<Employee> staff = new ArrayList<Employee>();   //用三个Employee对象填充数组
 
      staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));
      staff.add(new Employee("Harry Hacker", 50000, 1989, 10, 1));
      staff.add(new Employee("Tony Tester", 40000, 1990, 3, 15));
      ArrayList<Employee> list = new ArrayList<Employee>(); 
       
    //size()的用法
      int size=staff.size();
      System.out.println("arrayList中的元素个数是："+size);
      for(int i=0;i<staff.size();i++)
      {
          //get()的用法
          Employee e=staff.get(i);
          System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
                    + e.getHireDay());
      }
      //set()的用法
      staff.set(0, new Employee("llx", 20000, 1999, 11, 06));
      Employee e=staff.get(0);
      System.out.println("修改后的数据为：name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
                + e.getHireDay());
       
      //remove()的用法
      staff.remove(2);
      System.out.println("将第一个数据删除后：");
      int size1=staff.size();
      System.out.println("arrayList中的元素个数是："+size1);
      for(int i=0;i<staff.size();i++)
      {
          Employee p=staff.get(i);
          System.out.println("name=" + p.getName() + ",salary=" + p.getSalary() + ",hireDay="
                    + p.getHireDay());
      }
      
      // raise everyone's salary by 5% 
      for (Employee e1 : staff)    //把每个人的薪资提高%5
         e1.raiseSalary(5);
 
      // print out information about all Employee objects
      for (Employee e1 : staff)   //输出所有雇员对象的信息
         System.out.println("name=" + e1.getName() + ",salary=" + e1.getSalary() + ",hireDay="
            + e1.getHireDay());    //利用getName()，getSalary() 和getHireDay()方法输出所有雇员对象的信息
   }
}

运行结果如下：

测试程序3

l 编辑、编译、调试运行程序5-12（教材189页），结合运行结果理解程序；

l 掌握枚举类的定义及用法；

l 在程序中相关代码处添加新知识的注释；

l 删除程序中Size枚举类，背录删除代码，在代码录入中掌握枚举类的定义要求。（15分）

程序5-12：

package enums;

import java.util.*;

/**
 * This program demonstrates enumerated types.
 * @version 1.0 2004-05-24
 * @author Cay Horstmann
 */
public class EnumTest
{  
   public static void main(String[] args)
   {  
      var in = new Scanner(System.in);
      System.out.print("Enter a size: (SMALL, MEDIUM, LARGE, EXTRA_LARGE) ");
      String input = in.next().toUpperCase();
      Size size = Enum.valueOf(Size.class, input);
      System.out.println("size=" + size);
      System.out.println("abbreviation=" + size.getAbbreviation());
      if (size == Size.EXTRA_LARGE)
         System.out.println("Good job--you paid attention to the _.");      
   }
}

enum Size
{
   SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRA_LARGE("XL");

   private Size(String abbreviation) { this.abbreviation = abbreviation; }
   public String getAbbreviation() { return abbreviation; }

   private String abbreviation;
}

删除程序中Size枚举类，背录删除代码

package enums;

import java.util.*;

/**
 * This program demonstrates enumerated types.
 * @version 1.0 2004-05-24
 * @author Cay Horstmann
 */
public class EnumTest
{  
   public static void main(String[] args)
   {  
      var in = new Scanner(System.in);
      System.out.print("Enter a size: (SMALL, MEDIUM, LARGE, EXTRA_LARGE) ");
      String input = in.next().toUpperCase();
      Size size = Enum.valueOf(Size.class, input);  //静态方法valueOf
      System.out.println("size=" + size);
      System.out.println("abbreviation=" + size.getAbbreviation());
      if (size == Size.EXTRA_LARGE)
         System.out.println("Good job--you paid attention to the _.");      
   }
}
//在枚举类型中添加一些构造器、方法和域
enum Size
{
   SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRA_LARGE("XL");  //实例名

   private Size(String abbreviation) { this.abbreviation = abbreviation; }
   @Override
public String toString() {
    // TODO Auto-generated method stub
    return super.toString();
}


   public String getAbbreviation() {
    return abbreviation;
}
public void setAbbreviation(String abbreviation) {
    this.abbreviation = abbreviation;
}


private String abbreviation;
}

 运行结果：

测试程序4  录入以下代码，结合程序运行结果了解方法的可变参数用法（5分）

public class TestVarArgus {  
    public static void dealArray(int... intArray){  
        for (int i : intArray)  
            System.out.print(i +" ");  
          
        System.out.println();  
    }        
    public static void main(String args[]){  
        dealArray();  
        dealArray(1);  
        dealArray(1, 2, 3);  
    }  
}

 运行结果：

实验3 编程练习  参照输出样例补全程序，使程序输出结果与输出样例一致（10分）

public class Demo {
    public static void main(String[] args) {
        Son son = new Son();
        son.method();
    }
}
class Parent {
    Parent() {
        System.out.println("Parent's Constructor without parameter");
    }
    Parent(boolean b) {
        System.out.println("Parent's Constructor with a boolean parameter");
    }
    public void method() {
        System.out.println("Parent's method()");
    }
}
class Son extends Parent {
//补全本类定义
}

Parent's Constructor with a boolean parameter
Son's Constructor without parameter
Son's method()
Parent's method()

 修改后的代码如下：

public class Demo {
    public static void main(String[] args) {
        Son son = new Son();
        son.method();
    }
}
class Parent {
    Parent() {
        System.out.println("Parent's Constructor without parameter");
    }
    Parent(boolean b) {
        System.out.println("Parent's Constructor with a boolean parameter");
    }
    public void method() {
        System.out.println("Parent's method()");
    }
}
class Son extends Parent {
    Son(){
         super(false);
        System.out.println("Son's Constructor without parameter");
        System.out.println("Son's method()");
        }
    }

运行结果：

3. 实验总结：

本次试验学习了访问修饰符有四种public protected 默认的不写的 private，public 访问权限最大，同包（同文件夹）里面的类绝对是可以互相访问的，不同包中的类只要经过import得到了路径后也是可以通过类的对象访问的，protected 和 默认的比public访问权限都要小（不能在其他包中被访问除非继承这里是指protected）但他们两之间有细微的区别就是在不同包中的类继承protected和 默认的时候 ,继承的类能够访问用protected修饰的成员而不能访问默认即不写修饰符的成员，private 范围最小 只能在类内部的成员之间进行访问，外部的类是绝对没有办法通过对象访问到私有成员的,继承的类也不会继承private的成员在Java中，ArrayList类可以解决运行时动态更改数组的问题。ArrayList使用起来有点像数组，但是在添加或删除元素时，具有自动调节数组容量的功能，而不需要为此编写任何代码。在今后的学习中要多思考，多去理解代码，理解各种参数的使用方法。