之前的简要背景，以便我们可以在相同的波长上进行通信。我已经上过大约 8-10 门关于编程的大学类(class)，从数据结构到所有语言，再到特定语言(例如 java 和 c++)。我有点生疏了，因为我通常会休息 2-3 个月不写代码。这是我两年前开始考虑的一个个人项目。
好吧，具体到细节，还有一个具体问题，我的更改器(mutator)函数遇到了问题。看来我试图错误地访问私有(private)变量。问题是，我是否嵌套了太多的类并试图以错误的方式改 rebase 类变量。如果是这样，请向我指出正确的文献，或者确认这是我的问题，以便我可以重新研究这些信息。谢谢
package GroceryReceiptProgram;
import java.io.*;
import java.util.Vector;
public class Date {
private int hour, minute, day, month, year;
Date() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What's the hour? (Use 1-24 military notation");
hour = Integer.parseInt(keyboard.readLine());
System.out.println("what's the minute? ");
minute = Integer.parseInt(keyboard.readLine());
System.out.println("What's the day of the month?");
day = Integer.parseInt(keyboard.readLine());
System.out.println("Which month of the year is it, use an integer");
month = Integer.parseInt(keyboard.readLine());
System.out.println("What year is it?");
year = Integer.parseInt(keyboard.readLine());
keyboard.close();
} catch (IOException e) {
System.out.println("Yo houston we have a problem");
}
}
public void setHour(int hour) {
this.hour = hour;
}
public void setHour() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What hour, use military notation?");
this.hour = Integer.parseInt(keyboard.readLine());
keyboard.close();
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString());
}
}
public int getHour() {
return hour;
}
public void setMinute(int minute) {
this.minute = minute;
}
public void setMinute() {
try (BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in))) {
System.out.println("What minute?");
this.minute = Integer.parseInt(keyboard.readLine());
} catch (NumberFormatException e) {
System.out.println(e.toString() + ": doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString() + ": minute shall not cooperate");
} catch (NullPointerException e) {
System.out.println(e.toString() + ": in the setMinute function of the Date class");
}
}
public int getMinute() {
return minute;
}
public void setDay(int day) {
this.day = day;
}
public void setDay() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What day 0-6?");
this.day = Integer.parseInt(keyboard.readLine());
keyboard.close();
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString());
}
}
public int getDay() {
return day;
}
public void setMonth(int month) {
this.month = month;
}
public void setMonth() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What month 0-11?");
this.month = Integer.parseInt(keyboard.readLine());
keyboard.close();
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString());
}
}
public int getMonth() {
return month;
}
public void setYear(int year) {
this.year = year;
}
public void setYear() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What year?");
this.year = Integer.parseInt(keyboard.readLine());
keyboard.close();
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString());
}
}
public int getYear() {
return year;
}
public void set() {
setMinute();
setHour();
setDay();
setMonth();
setYear();
}
public Vector<Integer> get() {
Vector<Integer> holder = new Vector<Integer>(5);
holder.add(hour);
holder.add(minute);
holder.add(month);
holder.add(day);
holder.add(year);
return holder;
}
};
这显然是 Date 类，接下来是另一个基类 Location。
package GroceryReceiptProgram;
import java.io.*;
import java.util.Vector;
public class Location {
String streetName, state, city, country;
int zipCode, address;
Location() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What is the street name");
streetName = keyboard.readLine();
System.out.println("Which state?");
state = keyboard.readLine();
System.out.println("Which city?");
city = keyboard.readLine();
System.out.println("Which country?");
country = keyboard.readLine();
System.out.println("Which zipcode?");//if not u.s. continue around this step
zipCode = Integer.parseInt(keyboard.readLine());
System.out.println("What address?");
address = Integer.parseInt(keyboard.readLine());
} catch (IOException e) {
System.out.println(e.toString());
}
}
public void setZipCode(int zipCode) {
this.zipCode = zipCode;
}
public void setZipCode() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What zipCode?");
this.zipCode = Integer.parseInt(keyboard.readLine());
keyboard.close();
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString());
}
}
public void set() {
setAddress();
setCity();
setCountry();
setState();
setStreetName();
setZipCode();
}
public int getZipCode() {
return zipCode;
}
public void setAddress(int address) {
this.address = address;
}
public void setAddress() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What minute?");
this.address = Integer.parseInt(keyboard.readLine());
keyboard.close();
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString());
}
}
public int getAddress() {
return address;
}
public void setStreetName(String streetName) {
this.streetName = streetName;
}
public void setStreetName() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What minute?");
this.streetName = keyboard.readLine();
keyboard.close();
} catch (IOException e) {
System.out.println(e.toString());
}
}
public String getStreetName() {
return streetName;
}
public void setState(String state) {
this.state = state;
}
public void setState() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What minute?");
this.state = keyboard.readLine();
keyboard.close();
} catch (IOException e) {
System.out.println(e.toString());
}
}
public String getState() {
return state;
}
public void setCity(String city) {
this.city = city;
}
public void setCity() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What minute?");
this.city = keyboard.readLine();
keyboard.close();
} catch (IOException e) {
System.out.println(e.toString());
}
}
public String getCity() {
return city;
}
public void setCountry(String country) {
this.country = country;
}
public void setCountry() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What minute?");
this.country = keyboard.readLine();
keyboard.close();
} catch (IOException e) {
System.out.println(e.toString());
}
}
public String getCountry() {
return country;
}
};
他们的父类(正确的名称是什么？)类
package GroceryReceiptProgram;
import java.io.*;
public class FoodGroup {
private int price, count;
private Date purchaseDate, expirationDate;
private Location location;
private String name;
public FoodGroup() {
try {
setPrice();
setCount();
expirationDate.set();
purchaseDate.set();
location.set();
} catch (NullPointerException e) {
System.out.println(e.toString() + ": in the constructor of the FoodGroup class");
}
}
public void setPrice(int price) {
this.price = price;
}
public void setPrice() {
try (BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in))) {
System.out.println("What Price?");
price = Integer.parseInt(keyboard.readLine());
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString() + ": in the FoodGroup class, setPrice function");
} catch (NullPointerException e) {
System.out.println(e.toString() + ": in FoodGroup class. SetPrice()");
}
}
public int getPrice() {
return price;
}
public void setCount(int count) {
this.count = count;
}
public void setCount() {
try (BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in))) {
System.out.println("What count?");
count = Integer.parseInt(keyboard.readLine());
} catch (NumberFormatException e) {
System.out.println(e.toString() + ":doesnt seem to be a number");
} catch (IOException e) {
System.out.println(e.toString() + ": in the FoodGroup class, setCount()");
} catch (NullPointerException e) {
System.out.println(e.toString() + ": in FoodGroup class, setCount");
}
}
public int getCount() {
return count;
}
public void setName(String name) {
this.name = name;
}
public void setName() {
try {
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What minute?");
this.name = keyboard.readLine();
} catch (IOException e) {
System.out.println(e.toString());
}
}
public String getName() {
return name;
}
public void setLocation(Location location) {
this.location = location;
}
public Location getLocation() {
return location;
}
public void setPurchaseDate(Date purchaseDate) {
this.purchaseDate = purchaseDate;
}
public void setPurchaseDate() {
this.purchaseDate.set();
}
public Date getPurchaseDate() {
return purchaseDate;
}
public void setExpirationDate(Date expirationDate) {
this.expirationDate = expirationDate;
}
public void setExpirationDate() {
this.expirationDate.set();
}
public Date getExpirationDate() {
return expirationDate;
}
}
最后是主类，这样我就可以访问所有这些工作。
package GroceryReceiptProgram;
public class NewMain {
public static void main(String[] args) {
FoodGroup test = new FoodGroup();
}
}
如果有人进一步感兴趣，这里有一个 UML 链接。
最佳答案
您的 FoodGroup 有问题构造函数，您还没有初始化一些实例变量，因此它们采用 null默认值，给你带来问题:
public FoodGroup() {
//...
//null pointer exception here!
expirationDate.set();
//null pointer exception here!
purchaseDate.set();
//null pointer exception here!
location.set();
//...
}
这个问题可以通过在使用这些变量之前创建它们来解决:
public FoodGroup() {
//...
expirationDate = new Date();
//not null pointer exception!
expirationDate.set();
//similar to the other cases
//...
}
对此和 future 项目的一些建议:
- 不要创建与 Java API 中的类名称相似的类。例如，您的
Date类很容易被误解java.util.Date. - 请勿使用
Vector类，而是使用List<YourClass> list = new ArrayList<YourClass>()。更多信息请点击:What are the differences between ArrayList and Vector?和Why is Java Vector class considered obsolete or deprecated? (此来自Jon Skeet)。 - 尝试为您的类使用公共(public)构造函数。在您的情况下，您的程序将编译并运行只是因为所有类都在同一个包中，但如果它们位于不同的包中，则会出现问题，因为几乎所有构造函数都有
default可见性，只能被同一包的类看到。请注意:Controlling Access to Members of a Class -
FoodGroup不是父类，而是 1)FoodGroup之间的“has-a”关系和Date, 2)FoodGroup和Location。它可以被视为一个 Controller ，控制两个类实例的行为和 Activity 。 - 当您在此处或其他网站发布代码时，请发布 SSCCE而不是你的整个代码。这样，任何人都会更容易帮助您。
关于java - 空指针异常和带有继承和子类的突然 IOStream 闭包，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12667140/