CSC2 520 200 8 Spring Data Structures and Applications Assignment 1 FAQ Last updated: 4 Feb , 200 8

I collected some of the students’ questions together here. You may encounter the same problems as other students. Hope this can help your guys to do the assignment 1.

I collected some of the students’ questions together here.

You may encounter the same problems as other students.

Hope this can help your guys to do the assignment 1.

Q1 Q: when I try to follow the tutorial note to input the file, the Eclipse point out that can't found the file. My code: Scanner scanner = new Scanner(new File("d:/supermarket.dat")); and i have already out the file in that path. A: In this case, the path should be "d:\supermarket.dat". In the string, use “\” to represent character “”

Q: when I try to follow the tutorial note to input the file, the Eclipse point out that can't found the file.

My code:

Scanner scanner = new Scanner(new File("d:/supermarket.dat"));

and i have already out the file in that path.

A: In this case, the path should be "d:\supermarket.dat". In the string, use “\” to represent character “”

Q2 Q: I have define the class customer. when i want to use the method Customer(int T,int N, Float[] P) in supermarket class. The complier tell me that the constructor Customer is undefine. even if I use the Customer(int T,int N, Float[] P) as method, the complier still say that it is undefine. here is my code: for the constructor: public Customer(int T, int N, float[] P) { timeOfArrival=T; numberOfItems=N; System.arraycopy(P,0,itemPrices,0,P.length); } for the main class: int arriveTime = n; int ItemNum = value[n].length(); Float[] price = new Float[k+1]; Customer custom = new Customer(arriveTime, ItemNum, price); then the compiler said that the last command is error. A: From your description, it seems the compiler can not find the class. I suggest you to check the following two thins: 1. Is the class Customer defined in a individual file Customer.java? 2. Does the file Customer.java put in the same folder with Supermarket.java?

Q: I have define the class customer. when i want to use the method Customer(int T,int N, Float[] P) in supermarket class. The complier tell me that the constructor Customer is undefine. even if I use the Customer(int T,int N, Float[] P) as method, the complier still say that it is undefine.

here is my code:

for the constructor:

public Customer(int T, int N, float[] P) { timeOfArrival=T; numberOfItems=N; System.arraycopy(P,0,itemPrices,0,P.length); }

for the main class:

int arriveTime = n;

int ItemNum = value[n].length();

Float[] price = new Float[k+1];

Customer custom = new Customer(arriveTime, ItemNum, price);

then the compiler said that the last command is error.

A: From your description, it seems the compiler can not find the class.

I suggest you to check the following two thins:

1. Is the class Customer defined in a individual file Customer.java?

2. Does the file Customer.java put in the same folder with Supermarket.java?

Q3 (Error about Object Array) Q: I want to ask what is the java.lang.NullPointerException? And how can I solve the problem? A: The Java runtime throws java.lang.NullPointerException when an application attempts to use a null value as if it were an object. I guess it caused by using the array. Two possible explanations: 1. You've indexed past the array bounds 2. You haven't initialized the array correctly // example of an incorrectly initialized array: public class Test { public static void main(String args[]) { String sa[] = new String[5]; sa[0].charAt(0); } } // example of a correctly initialized array: public class Test { public static void main(String args[]) { String sa[] = new String[5]; for(int i = 0; i < 5; i++) { sa[i] = new String(); } sa[0].charAt(0); } }

Q: I want to ask what is the java.lang.NullPointerException? And how can I solve the problem?

A: The Java runtime throws java.lang.NullPointerException when an application attempts to use a null value as if it were an object. I guess it caused by using the array.

Two possible explanations:

1. You've indexed past the array bounds 2. You haven't initialized the array correctly

// example of an incorrectly initialized array:

public class Test {

public static void main(String args[]) {

String sa[] = new String[5];

sa[0].charAt(0);

}

}

// example of a correctly initialized array:

public class Test {

public static void main(String args[]) {

String sa[] = new String[5];

for(int i = 0; i < 5; i++) {

sa[i] = new String();

}

sa[0].charAt(0);

}

}

Q4 請問我用不用在每一個會有機會有 exception 的地方加上 throw HeyException 呢 ? 答：我建議你可以這樣做，因爲這樣有助于你形成良好的編程習慣。在我們的作用中，良好的編程風格會有部分的分數。

請問我用不用在每一個會有機會有 exception 的地方加上 throw HeyException 呢 ?

答：我建議你可以這樣做，因爲這樣有助于你形成良好的編程習慣。在我們的作用中，良好的編程風格會有部分的分數。

Q5 我需不需要把 comment 寫在 source code 內 , 還是在 header 簡述即可 ? 答： Comment 寫在 Code 内，在 Header 内是對整個 Class 的一個簡單描述

我需不需要把 comment 寫在 source code 內 , 還是在 header 簡述即可 ?

答： Comment 寫在 Code 内，在 Header 内是對整個 Class 的一個簡單描述

Q6 請問你有沒有一個 supermarket.dat 可測試 question2 的所有 function, 我已嘗試使用你所提供的 supermarket.dat 以及根據你的 tutorial note 用的 case 製做的 supermarket.dat 來測試 , 均能正常運作 , 這是否已經沒問題嗎 ? 答：對不起，現在沒有， Test Case 會在檢查作業的時候才去設計。你可以自行設計一些數據，然後自己根據過程去計算結果，看看與程序結果是否一致來驗證。

請問你有沒有一個 supermarket.dat 可測試 question2 的所有 function, 我已嘗試使用你所提供的 supermarket.dat 以及根據你的 tutorial note 用的 case 製做的 supermarket.dat 來測試 , 均能正常運作 , 這是否已經沒問題嗎 ?

答：對不起，現在沒有， Test Case 會在檢查作業的時候才去設計。你可以自行設計一些數據，然後自己根據過程去計算結果，看看與程序結果是否一致來驗證。

Q7 assignment 的 deadline 是中午 12 時嗎 ? 如是 , 可以押後至晚上 11:55pm 嗎 ? 答： Deadline 是晚上 12 點

assignment 的 deadline 是中午 12 時嗎 ? 如是 , 可以押後至晚上 11:55pm 嗎 ?

答： Deadline 是晚上 12 點

Q8 About Scanner Please follow the tutorial 02 about how to use the scanner

Please follow the tutorial 02 about how to use the scanner