张云飞 201771010143《面向对象程序设计（java）》第七周学习总结

Posted 2021-01-12 fairber

实验七继承附加实验

实验时间2018-10-11

1、实验目的与要求

（1）进一步理解4个成员访问权限修饰符的用途； 

1.仅对本类可见-private

2.对所有类可见-public

3.对本包和所有子类可见-protected

4.对本包可见-默认，不需要修饰符

 

掌握Object类的常用API用法；

toString方法：它用于返回对象值的字符串

equals方法：检测一个对象是否等于另一个对象（不同于==）

hasCode方法：获得散列码（其值为对象的存储地址）

1.子类继承父类的成员变量

　　当子类继承了某个类之后，便可以使用父类中的成员变量，但是并不是完全继承父类的所有成员变量。具体的原则如下：

1）能够继承父类的public和protected成员变量；不能够继承父类的private成员变量；

2）对于父类的包访问权限成员变量，如果子类和父类在同一个包下，则子类能够继承；否则，子类不能够继承；

3）对于子类可以继承的父类成员变量，如果在子类中出现了同名称的成员变量，则会发生隐藏现象，即子类的成员变量会屏蔽掉父类的同名成员变量。如果要在子类中访问父类中同名成员变量，需要使用super关键字来进行引用。super.属性名

2.子类继承父类的方法

　　子类并不是完全继承父类的所有方法。

1）能够继承父类的public和protected成员方法；不能够继承父类的private成员方法；

2）对于父类的包访问权限成员方法，如果子类和父类在同一个包下，则子类能够继承；否则，子类不能够继承；

3）对于子类可以继承的父类成员方法，如果在子类中出现了同名称的成员方法，则称为覆盖，即子类的成员方法会覆盖掉父类的同名成员方法。如果要在子类中访问父类中同名成员方法，需要使用super关键字来进行引用。super.方法名

2、实验内容和步骤

实验1  补充以下程序中主类内main方法体，以验证四种权限修饰符的用法。

public class TEST1 { private String t1 = "这是TEST1的私有属性"; public String t2 = "这是TEST1的公有属性"; protected String t3 = "这是TEST1受保护的属性"; String t4 = "这是TEST1的默认属性"; private void tese1() { System.out.println("我是TEST1用private修饰符修饰的方法"); } public void tese2() { System.out.println("我是TEST1用public修饰符修饰的方法"); } protected void tese3() { System.out.println("我是TEST1用protected修饰符修饰的方法"); } void tese4() { System.out.println("我是TEST1无修饰符修饰的方法"); } } public class TEST2 extends TEST1{ private String e1 = "这是TEST2的私有属性"; public String e2 = "这是TEST2的公有属性"; protected String e3 = "这是TEST2受保护的属性"; String e4 = "这是TEST2的默认属性"; public void demo1() { System.out.println("我是TEST2用public修饰符修饰的方法"); } private void demo2() { System.out.println("我是TEST2用private修饰符修饰的方法"); } protected void demo3() { System.out.println("我是TEST2用protected修饰符修饰的方法"); } void demo4() { System.out.println("我是TEST2无修饰符修饰的方法"); } } public class Main { public static void main(String[] args) { TEST2 test2 = new TEST2(); /*以下设计代码分别调用 demo1 demo2 demo3 demo4 test1 test2 test3 test4方法和t1 t2 t3 t3 e1 e2 e3 e4属性，结合程序运行结果理解继承和权限修饰符的用法与区别*/ } }

public class Main {

    public static void main(String[] args) {

        TEST2 test2 = new TEST2();

        test2.demo1();

        test2.demo3();

        test2.demo4();

        test2.test2();

        test2.test3();

        test2.test4();

        String e2=test2.e2;

        String e3=test2.e3;

        String e4=test2.e4;        

        System.out.println(e2);

        System.out.println(e3);

        System.out.println(e4);

        System.out.println(test2.t2);

        System.out.println(test2.t3);

        System.out.println(test2.t4);

        }

}

public class TEST1 {

    private String t1 = "这是TEST1的私有属性";

    public String t2 = "这是TEST1的公有属性";

    protected String t3 = "这是TEST1受保护的属性";

    String t4 = "这是TEST1的默认属性";

    private void test1() {

        System.out.println("我是TEST1用private修饰符修饰的方法");

    }

    public void test2() {

        System.out.println("我是TEST1用public修饰符修饰的方法");

    }

    protected void test3() {

        System.out.println("我是TEST1用protected修饰符修饰的方法");

    }

    void test4() {

        System.out.println("我是TEST1无修饰符修饰的方法");

    }

}

 

TEST1

public class TEST2 extends TEST1{

    private String e1 = "这是TEST2的私有属性";

    public String e2 = "这是TEST2的公有属性";

    protected String e3 = "这是TEST2受保护的属性";

    String e4 = "这是TEST1的默认属性";

    public void demo1() {

        System.out.println("我是TEST2用public修饰符修饰的方法");

    }

    private void demo2() {

        System.out.println("我是TEST2用private修饰符修饰的方法");

    }

    protected void demo3() {

        System.out.println("我是TEST2用protected修饰符修饰的方法");

    }

    void demo4() {

        System.out.println("我是TEST2无修饰符修饰的方法");

    }

}

 

TEST2

Main

 

实验2  第五章测试程序反思，继承知识总结。

测试程序1：

? 编辑、编译、调试运行教材程序5-8、5-9、5-10（教材174页-177页）；

? 结合程序运行结果，理解程序代码，掌握Object类的定义及用法；

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)

   {

      // 快速测试，看看这些对象是否相同

      if (this == otherObject) return true;

 

      // 如果显式参数为空，则必须返回false

      if (otherObject == null) return false;

 

      // 如果类不匹配，它们就不能相等

      if (getClass() != otherObject.getClass()) return false;

 

      // 现在我们知道otherObject是一个非空雇员

      Employee other = (Employee) otherObject;

 

      // 测试字段是否具有相同的值

      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

            + "]";

   }

}

 

 

 

 

package equals;

public class Manager extends Employee//子类Manager继承父类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;

      Manager other = (Manager) otherObject;

      // super.equals检查这个和其他属于同一个类

      return bonus == other.bonus;

   }

 

   public int hashCode()

   {

      return java.util.Objects.hash(super.hashCode(), bonus);

   }

 

   public String toString()

   {

      return super.toString() + "[bonus=" + bonus + "]";

   }

}

 

 

 

/**

 * This program demonstrates the equals method.

 * @version 1.12 2012-01-26

 * @author Cay Horstmann

 */public class EqualsTest

{

   public static void main(String[] args)

   {

      Employee alice1 = new Employee("Alice Adams", 75000, 1987, 12, 15);

      Employee alice2 = alice1;

      Employee alice3 = new Employee("Alice Adams", 75000, 1987, 12, 15);

      Employee 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);

 

      Manager carl = new Manager("Carl Cracker", 80000, 1987, 12, 15);

      Manager 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());

   }

}

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)

   {

      // 快速测试，看看这些对象是否相同

      if (this == otherObject) return true;

 

      // 如果显式参数为空，则必须返回false

      if (otherObject == null) return false;

 

      // 如果类不匹配，它们就不能相等

      if (getClass() != otherObject.getClass()) return false;

 

      // 现在我们知道otherObject是一个非空雇员

      Employee other = (Employee) otherObject;

 

      // 测试字段是否具有相同的值

      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

            + "]";

   }

}

 

 

 

 

package equals;

public class Manager extends Employee//子类Manager继承父类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;

      Manager other = (Manager) otherObject;

      // super.equals检查这个和其他属于同一个类

      return bonus == other.bonus;

   }

 

   public int hashCode()

   {

      return java.util.Objects.hash(super.hashCode(), bonus);

   }

 

   public String toString()

   {

      return super.toString() + "[bonus=" + bonus + "]";

   }

}

 

 

 

/**

 * This program demonstrates the equals method.

 * @version 1.12 2012-01-26

 * @author Cay Horstmann

 */public class EqualsTest

{

   public static void main(String[] args)

   {

      Employee alice1 = new Employee("Alice Adams", 75000, 1987, 12, 15);

      Employee alice2 = alice1;

      Employee alice3 = new Employee("Alice Adams", 75000, 1987, 12, 15);

      Employee 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);

 

      Manager carl = new Manager("Carl Cracker", 80000, 1987, 12, 15);

      Manager 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());

   }

}

 

 

测试程序2：

编辑、编译、调试运行教材程序5-11（教材182页）；

结合程序运行结果，理解程序代码，掌握ArrayList类的定义及用法；

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)

   {

      // 用三个Employee对象填充staff数组列表

      ArrayList<Employee> staff = new ArrayList<>();

 

      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));

 

      // 把每个人的薪水提高5%

      for (Employee e : staff)

         e.raiseSalary(5);

 

      // 打印所有Employee对象的信息

      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;

   }

}

 

 

测试程序3：

编辑、编译、调试运行程序5-12（教材189页）；

结合运行结果，理解程序代码，掌握枚举类的定义及用法；

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)

   {  

      Scanner 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)//判断语句

         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;

}

 

 

实验3：采用个人账号登录https://pintia.cn/，完成《2018秋季西北师范大学面向对象程序设计（Java）（ch1-ch5）测试题2》，测试时间60分钟；

实验4: 课后完成实验3未完成的测试内容。

本周学习总结：在本周的学习过程中，实验课上听过了学长的讲解后对于四个修饰符有了更加透彻的理解，最初使用的时候只是大概将其敲上去，当时并不理解各个修饰符在功能上的不同点。1.仅对本类可见-private2.对所有类可见-public3.对本包和所有子类可见-protected4.对本包可见-默认，不需要修饰符。

第二：在pintia平台上做编程题目时，总是得到结果错误的反馈，在及时和学长沟通之后，得到了两个收获，一个是抽象类也可以和主类放在一个class中运行。另外就是时刻注意程序的输入输出的格式是否和题目要求中的一致。

 

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