好的，我有一个作为联系人列表的小程序。它是由一个二维数组构造的，它需要用户输入来填充总共10个联系人;因此，该数组有10行4列，由名、姓、电话号码和年龄组成。有一个菜单，用户可以选择1)添加联系人，2)删除联系人，3)显示联系人，以及4)退出程序。我知道这可能看起来像一个粗糙的，蛮力的方法，但它要求我们不要使用任何东西，但我们已经学过的东西，其中不包括方法，如ArrayList, LinkedList, Collections, HashMaps等。我的问题是，程序工作正常，直到我删除一个联系人。当我再次得到菜单时，我想重新添加联系人，它就会循环回到菜单。这一定是一些小语法错误，但我不确定在哪里。我将展示代码和输出，以便让您了解它从哪里开始出错。*注:我并不是要求代码本身，而是要求建议和指导，让我意识到我的错误所在。
代码: import java.util.Scanner;
public class ContactList {
public static void main(String[] args) {
new ContactList ();
}
public ContactList () {
Scanner input = new Scanner(System.in);
String[][] contactList = new String[10][4];
System.out.println("Welcome to your Contact organizer.");
System.out.println("You can store " + contactList.length + " contacts. " );
System.out.println("Please enter your choice from the list below: ");
System.out.println();
while(true){
System.out.println("1: Add a Contact"); //the user options
System.out.println("2: Remove a Contact");
System.out.println("3: Display your Contacts");
System.out.println("4: Exit this program");
int userSelection = input.nextInt();
switch(userSelection) {
case 1:
addContact(contactList);
break;
case 2:
removeContact(contactList);
break;
case 3:
displayContacts(contactList);
break;
case 4:
System.out.println("Goodbye.");
System.exit(0);
}
}
}
private void addContact(String contactList[][]) {
Scanner input = new Scanner(System.in);
for(int i = 0; i < contactList.length; i++) {
if(contactList[i][0] == null) {
System.out.print("Enter the contact's first name: ");
contactList[i][0] = input.nextLine().trim(); //.trim() eliminates any accidental white spaces
System.out.print("Enter the contact's last name: ");
contactList[i][1] = input.nextLine().trim();
System.out.print("Enter the contact's phone number: ");
contactList[i][2] = input.nextLine().trim();
System.out.print("Enter the contact's age: ");
contactList[i][3] = input.nextLine().trim();
break;
}
}
}//end add method
private void removeContact(String contactList[][]){
Scanner input = new Scanner(System.in);
System.out.println("Enter the first name of contact you wish to remove: ");
String deleteFirst = input.nextLine().trim();
System.out.println("Enter the last name of contact you wish to remove: ");
String deleteLast = input.nextLine().trim();
for(int i = 0; i < contactList.length; i++) {
for(int j = 0; j < contactList[i].length; j++) {
if(deleteFirst.equals(contactList[i][0]) && deleteLast.equals(contactList[i][1])) {
System.out.println("Contact successfully removed. n n");
contactList[i][0] = null;
contactList[i][1] = null;
contactList[i][2] = null;
contactList[i][3] = null;
break;
}
}
}
}//end remove method
private void displayContacts(String contactList[][]) {
for(int i = 0; i < contactList.length; i++) {
for(int j = 0; j < contactList[i].length; j++) {
if(contactList[i][j] == null) {
contactList[i][j] = (" "); //if user displays before all contacts are entered, it will display blank rather than null null null, etc.
}
System.out.print(contactList[i][j] + " ");
}
System.out.println();
}
}//end display method
}//end class
我知道removeccontact方法可能看起来很可怕，但这是我知道如何删除整行的唯一方法。我一直在想我应该在那个方法中创建一个新数组，但我还不知道怎么做。
输出如下:
Welcome to your Contact organizer.
You can store 10 contacts.
Please enter your choice from the list below:
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
1
Enter the contact's first name: John
Enter the contact's last name: Doe
Enter the contact's phone number: 1234567
Enter the contact's age: 34
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
1
Enter the contact's first name: Joe
Enter the contact's last name: Bob
Enter the contact's phone number: 4567890
Enter the contact's age: 30
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
3
John Doe 1234567 34
Joe Bob 4567890 30 --contacts display just fine so far
--I know there are a lot of spaces since technically there is
still data here, albeit blank spaces. Perhaps I need to make it a
new array each time something is added? I'll have to figure out
how to do that. For now, it looked far better than:
null null null null
null null null null
etc...
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
2
Enter the first name of contact you wish to remove:
Joe
Enter the last name of contact you wish to remove:
Bob
Contact successfully removed.
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
3
John Doe 1234567 34 --output displays contact removed
1: Add a Contact --and this is where is begins to mess up.
2: Remove a Contact Why now?
3: Display your Contacts
4: Exit this program
1
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
1
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
1
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
3
John Doe 1234567 34 --I can still display contacts. ????
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
1
1: Add a Contact
2: Remove a Contact
3: Display your Contacts
4: Exit this program
4
Goodbye. --and I can exit. I just can no longer add.
Process finished with exit code 0
我发现了一个问题:
if(contactList[i][j] == null) {
contactList[i][j] = (" "); //if user displays before all contacts are entered, it will display blank rather than null null null, etc.
}
我将其更改为只在联系人不为空时显示联系人，如下所示:
if(contactList[i][j] != null) {
System.out.print(contactList[i][j] + " ");
}
我现在可以返回到我的菜单并添加另一个联系人。我更希望输出没有留下空白，但我会自己弄清楚，因为它与我的原始帖子无关。
虽然我不知道为什么这个问题会发生(因为我没有收到任何答案或评论，只有一个毫无意义的反对投票)，我至少解决了我的问题。我唯一的猜测是，当我将联系人赋值为null，然后将该空值赋给空白(" ")时，程序认为它在技术上仍然是满的，因为数组现在被空格的unicode值填充("u0020")。因此，我对输出的美学尝试在程序中创造了一个中断。