201871010106-丁宣元 《面向对象程序设计（java)》第七周学习总结

201871010106-丁宣元 《面向对象程序设计（java)》第七周学习总结

正文开头:

项目	内容
这个作业属于哪个课程	https://home.cnblogs.com/u/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。

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。

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);//p1无法打印，因为是私有属性
        System.out.println(p3);
        System.out.println(p4);//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();
        parent.pMethod2();
        parent.pMethod3();
        parent.pMethod4();//分别尝试用parent调用Parent类的方法
        son.sMethod();//用son调用Son类的方法
        son.sMethod1();
        son.sMethod4();//son.sMethod2()是private，只能在son类中使用
    }
}

结果：

注：protected和friendly都只能访问同一个包中的，但protected权限更大些，可访问不同包，但必须是子类继承父类。

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。

1.程序代码

5-8EqualsTest.java

package equals;

/**
 * This program demonstrates the equals method.
 * @version 1.12 2012-01-26
 * @author Cay Horstmann
 */
public class EqualsTest  //主类
{
   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());
   }
}

5-9Empolyee.java

package equals;

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

public class Employee //用户自定义类
{
   private String name; //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)//访问器
   {
      double raise = salary * byPercent / 100;
      salary += raise;
   }

   public boolean equals(Object otherObject)
   {
      // a quick test to see if the objects are identical 测试几个类是否相同，若引用同一个，则相等
      if (this == otherObject) return true;

      // must return false if the explicit parameter is null 若显式参数为空必须返回false
      if (otherObject == null) return false;

      // if the classes don't match, they can't be equal若几个类不匹配，则它们不相等
      if (getClass() != otherObject.getClass()) return false;

      // now we know otherObject is a non-null Employee  已知otherObject是一个非空雇员
      var other = (Employee) otherObject;

      // test whether the fields have identical values 检测是否具有相同的值
      return Objects.equals(name, other.name)
         && salary == other.salary && Objects.equals(hireDay, other.hireDay);
   }

   public int hashCode()//重写hashcode方法，使得相等的两个对象获取的HashCode相等
   {
      return Objects.hash(name, salary, hireDay);
   }

   public String toString()   //其他类型数据转为字符串型的数据
   {
      return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay="
         + hireDay + "]";
   }
}

5-10Manager.java

package equals;

public class Manager extends Employee//子类Manager继承Employee
{
   private double bonus;

   public Manager(String name, double salary, int year, int month, int day)
   {
      super(name, salary, year, month, day);//子类调用超类中的属性
      bonus = 0;
   }

   public double getSalary()//访问器
   {
      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  使用super.equals检查这个类和其他的是否属于同一个类
      return bonus == other.bonus;
   }

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

   public String toString()// toString()方法，可自动生成
   {
      return super.toString() + "[bonus=" + bonus + "]";
   }
}

结果：

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

代码:

Employee.java

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;
   }

@Override
public boolean equals(Object otherObject) {  //重写equals方法
    // 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() {   //重写hashCode方法
    // TODO Auto-generated method stub
    return Objects.hash(name,salary,hireDay);
}

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

Manager.java

package equals;

public class Manager extends Employee  //Manager类（子类）继承Employee类（父类）
{
   private double bonus;//私有属性

   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;
   }

@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+"]";
}

}

EqualsTest.java

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());
   }
}

结果：

测试程序2：

　　　　 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；

　　　   掌握ArrayList类的定义及用法；

　　　　 在程序中相关代码处添加新知识的注释；

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

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用三个Employee类填充staff数组列表
      var staff = new ArrayList<Employee>();//动态数组，可以灵活设置数组的大小

      staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));//在列表中插入元素，
      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%每个人的薪水提高5%
      for (Employee e : staff)
         e.raiseSalary(5);

      // print out information about all Employee objects
      for (Employee e : staff)//for each循环，遍历数组列表
         System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
            + e.getHireDay());
   }
}

Employee.java

package arrayList;

import java.time.*;

public class Employee
{
   private String name;//私有属性
   private double salary;//私有属性
   private LocalDate hireDay;//私有属性

   public Employee(String name, double salary, int year, int month, int day)//构造器
   {
      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)//访问器
   {
      double raise = salary * byPercent / 100;
      salary += raise;
   }
}

结果：

注：ArrayList ：动态数组，可以动态增加和减少元素，灵活设置数组的大小。
　　            三个构造器： public ArrayList();默认构造器  public ArrayList(ICollection); 
　　　　　　　　public ArrayList(int); 指定大小来初始化内部的数组

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

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)
   {
      // fill the staff array list with three Employee objects
      var staff = new ArrayList<Employee>();

      staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));//在列表中插入元素，
      staff.add(new Employee("Harry Hacker", 50000, 1989, 10, 1));
      staff.add(new Employee("Tony Tester", 40000, 1990, 3, 15));
      System.out.println(staff.get(1));
      staff.set(2, new Employee("DXY", 1000, 1999, 7, 21));
      System.out.println(staff.size());
      staff.remove(0);

      // raise everyone's salary by 5%
      for (Employee e : staff)
         e.raiseSalary(5);

      // print out information about all Employee objects
      for (Employee e : staff)//for each循环，遍历数组列表
         System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
            + e.getHireDay());
   }
}

注：get()方法获得下标的储存位置

　　　   set()方法修改ArrayList<>并添加new Employee("DXY", 1000, 1999, 7, 21)

　　　　get()方法获得元素输出

　　　　remove()方法删除数组元素

　　　　size()方法得到长度。

　　 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；

　　　　掌握枚举类的定义及用法；

　　　　在程序中相关代码处添加新知识的注释；

　　　   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。

5-12：

package enums;

import java.util.*;

/**
 * This program demonstrates enumerated types.
 * @version 1.0 2004-05-24
 * @author Cay Horstmann
 */
public class EnumTest//主类
{
   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();  //字符串转换为大写
      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//枚举类型，是enum的子类
{
   SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRA_LARGE("XL");//需传入参数

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

   private String abbreviation;
}

结果：

删除程序中Size枚举类，背录删除代码

代码：

package equals;

public class Manager extends Employee  //Manager类（子类）继承Employee类（父类）
{
   private double bonus;//私有属性

   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;
   }

@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+"]";
}

}

　　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

代码：

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);
    }
}

结果：

注：int... intArray，...是可变参数，是int型，也可以改为其他型的   eg:String...StringArray

　　   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：

public class Demo1 {
      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
     Son(){
         super(false);
         System.out.println("Son's Constructor without parameter");
     }
     public void method() {
         System.out.println("Son's method()");
         super.method();
     }
 }

结果：

3. 实验总结：

　　通过本次实验，我学习到了：1.四种访问权限修饰符的使用特点   2.Object类   3.ArrayList类的方法    4.枚举类定义方法及用途

通过本次实验，加深了我对java继承特点的理解，并在助教讲解后对四种访问权限修饰符有了更深层面的认识，掌握了ArrayList类，枚举类，对java的学习有了更深的了解。通过线上线下学习，及实验课的练习，我对继承这一章的知识有了明确的把握，但在知识掌握上还是不足。在实验中遇到了许多问题，归根结底是知识掌握的不熟，在同学的帮助下基本解决了问题。在课余时间还是要加强对知识的理解，多练习。