201871020225-牟星源《面向对象程序设计(java)》第七周学习总结

201871020225-牟星源《面向对象程序设计(java)》第七周学习总结

博文正文开头:

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/11435127.html

作业学习目标

  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类的定义方法及用途;
  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。

随笔博文正文内容:

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。

(1)程序代码

实验代码:

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(p2);//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 sMethod3() {

       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();

    parent.pMethod2() ;  //分别尝试用parent调用Paren类的方法、用son调用Son类的方法 

    }

}

parent代码:

package mxy;

public 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");

    }

}

son代码:

package first;

import mxy.Parent;

public 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(p2);//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 sMethod3() {

        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");

    }  

}

(2)运行结果如下:

Parent1:

 

Parent2:

 

Parent3:

 

Parent4:

 

Son1:

 

Son2:

 

Son3:

 

Son4:

 

实验2:导入第5章以下示例程序,测试并进行代码注释。

实验2:测试程序1

l  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);

5.8代码:

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)

   {

      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());

   }

}

5.9代码:

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

      Employee 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 + "]";

   }

}

5.10代码:

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;

      Manager 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:

 

l  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。

(1)代码

Employee类重写后代码如下:

package equals;

import java.time.*;

import java.util.Objects;

public class Employee

{

   private String name;    //创建三个私有属性

   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;   //定义局部变量

      salary += raise;

   }

@Override

public int hashCode() {   //重写hashCode方法,使相等的两个对象获取的HashCode也相等

    // TODO Auto-generated method stub

    return Objects.hash(name, salary, hireDay);

}

@Override

public boolean equals(Object obj) {

    // TODO Auto-generated method stub

    if (this == obj) return true;     //快速测试几个类的根是否相同,即是否是同一个超类。这个if语句判断两个引用是否是同一个,如果是同一个,那么这两个对象肯定相等。

    if (obj == null) return false;   //如果显示参数为空,则返回false

    if (getClass() !=obj.getClass()) return false;   //用getClass()方法得到对象的类。如果几个类不匹配,则它们不相等

    //其他对象是非空Employee类

    //在以上判断完成,再将得到的参数对象强制转换为该对象,考虑到父类引用子类的对象的出现,然后再判断对象的属性是否相同

    Employee other = (Employee) obj;

    //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);

 }

@Override

public String toString() {  //把其他类型的数据转为字符串类型的数据(toString方法可以自动生成)

    // TODO Auto-generated method stub

    return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay=" + hireDay + "]";

}

}

Manager类重写之后代码如下:

package equals;

public class Manager extends Employee     //子类:Manager类继承Employee类

{

   private double bonus;     //创建私有属性bouns

   public Manager(String name, double salary, int year, int month, int day)

   {

      super(name, salary, year, month, day);    //子类直接调用超类中已创建的属性

      bonus = 0;      //给bouns赋初值为空

   }

   public double getSalary()//访问器

   {

      double baseSalary = super.getSalary();

      return baseSalary + bonus;

   }

   public void setBonus(double bonus)   //更改器

   {

      this.bonus = bonus;

   }

   public boolean equals(Object otherObject)   //快速测试几个类的根是否相同,即是否是同一个超类

   {

      if (!super.equals(otherObject)) return false;

      Manager other = (Manager) otherObject;

       //使用super.equals检查这个类和其他是否属于同一个类

      return bonus == other.bonus;

   }

   public int hashCode()    //重写hashCode方法,使相等的两个对象获取的HashCode也相等

   {

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

   }

   public String toString()    //把其他类型的数据转为字符串类型的数据(toString方法可以自动生成)

   {

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

   }

}

EmployeeTest类代码如下:

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)

   {

      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());

   }

}

(2)运行结果如下:

 

实验2: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;

5.11代码:

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

      ArrayList 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:

 

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

代码为:

package 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:

 

实验2: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;

代码为:

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)

         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;

}

运行结果为:

 

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。

代码为:

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values方法返回枚举的所有值的数组

      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;

}//调用构造函数

运行结果为:

 

实验2: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

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); 

    } 

}

代码为:

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。

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

}

程序运行结果如下:

Parent's Constructor with a boolean parameter

Son's Constructor without parameter

Son's method()

Parent's method()

代码为:

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); 

    } 

}

运行结果为:

 

3. 实验总结:(15分)

    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。多进行编程练习,以提高编程能力。

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转载自www.cnblogs.com/muxingyuan/p/11673504.html