访问Java中的部分数组？

Question

Hello persons of StackOverflow,

I am having trouble with my current code. I keep getting a null pointer exception when I attempt to see if an array contains a certain search value. Here is my current code, and here are the criteria for which I have to complete it with. This is my first post here, so all beneficial criticisms are accepted.

Criteria: Create a program that let's the user enter information into an address book, and then search the names in the address book. You must store the following in the address book: Name Phone Number Email Address The program will allow the user to enter as many people as they want into the address book, up to 100. The user will enter an empty name to indicate they are done entering names. After that the user will enter partial names to search for people in the address book. For full credit this search should find partial names (see screenshot for examples). You program does not need to be case insensitive (ie it can be case sensitive). You program should display all the information for all address book entries that match the search criteria. The results should be in a chart format (see screenshot for example). If the user enters a blank name to search for the program should end. You must use three parallel one dimensional arrays. You must use a global constant to set the maximum number of entries in the address book to 100.

package assignments;

import global.Cod;


public class Homework_08 
{
    public static final int MAXIMUM_ENTRIES = 100;

    public static void main(String[] args) 
    {
        String name[] = new String[MAXIMUM_ENTRIES];
        String phoneNumber[] = new String[MAXIMUM_ENTRIES];
        String email[] = new String[MAXIMUM_ENTRIES];

        String searchValue;
        int index = 0;
        boolean match = false;

        if (!name.equals(MAXIMUM_ENTRIES))
        {
            for (index = 0; index < MAXIMUM_ENTRIES; index++) {
                System.out.print("Enter name (Or <ENTER> if done): ");
                name[index] = Cod.next();

                if (!name[index].equals("")) {
                    System.out.print("Enter phone number: ");
                    phoneNumber[index] = Cod.next();

                    System.out.print("Enter email address: ");
                    email[index] = Cod.next();
                } 
                else if (name[index].equals(""))
                {
                    System.out.print("Enter search value: ");
                    searchValue = Cod.next();

                    while (!match && index < MAXIMUM_ENTRIES)
                    {
                        if (name[index].contains(searchValue)) {
                            match = true;
                        }
                        else
                        {
                            index++;
                        }
                    }

                    System.out.println("Name                 Phone          Email");
                    System.out.println("----                 -----          -----");

                    if (match) 
                    {
                        System.out.println(name[index] + phoneNumber[index] + email[index]);
                    }
                    else
                    {
                        System.out.println("                                         ");
                    }
                }
            }
        }
    } //main()
} //class

The Cod import statements are pretty much simpler ways for me to do the scanner. They work the same way, where as next() is simply asking for the next string, and every other possibility is self-explanatory.

Thank you.

Answer 1

The problem is that your while (!match && index < MAXIMUM_ENTRIES) loop starts searching at the last entry in your array (ie the current value of index ).

The enclosing for() loop updates index every time you get a name, phone, & email. That's good. But when you search you need to start your search at array index 0 and go to index (ie the current count of how many valid elements are in the array).

Try breaking out of the data-entry loop when you get an empty name string and making a new loop to search through the names (and only search up to index names).

Also, you don't need to check for name being empty twice. This code:

if (!name[index].equals("")) {

tests to see if name is non-empty, yet in the else block that follows you test it again:

else if (name[index].equals(""))

Since you already know it is non-empty from the first test, there is no reason to do it again. Just say else {

That's not a bug per-se, just an optimization and a way you need to remember to look at if/else blocks.

Answer 2

Here I can see two problems 1) you dont have null check for name[index]. As you are initializing array, all the elements initial value will be null. 2) you are using same index for iteration, This may cause new addition of contacts will go to random locations. Better use seperate index searchIndex for search iteration.

int searchIndex = 0;
while (!match && searchIndex< MAXIMUM_ENTRIES)
                {
                    if (null!=name[searchIndex] && name[searchIndex].contains(searchValue)) {
                        match = true;
                    }
                    else
                    {
                        searchIndex++;
                    }
                }

Answer 3

import global.Cod;
import java.util.*;
import java.io.*;
public class Homework_08 
{
    public static final int MAXIMUM_ENTRIES = 100;

    public static void main(String[] args) 
    {
        String names[] = new String[MAXIMUM_ENTRIES];
        String phoneNumbers[] = new String[MAXIMUM_ENTRIES];
        String emails[] = new String[MAXIMUM_ENTRIES];
        Scanner scan = new  Scanner(System.in);
        String searchValue,name,mail,pno;
        int index = 0,i;
        boolean match = false;

          for (index = 0; index < MAXIMUM_ENTRIES; index++) {
                System.out.print("Enter name (Or <ENTER> if done): ");
                name= scan.nextLine(); 
                if(name=="")break;
                else{
                    System.out.print("Enter phone number: ");
                    pno = scan.nextLine(); 
                    System.out.print("Enter email address: ");
                    mail= scan.nextLine(); 
                    names[index]=name;
                    phoneNumbers[index]=pno;
                    emails[index]=mail;

                }
            }
            System.out.print("Enter name to search (Or <ENTER> if done): ");
            searchValue= scan.nextLine(); 
            while(searchValue!=""){
             for(i=0;i<index;i++){
                if(names[i].contains(searchValue)){
                    System.out.println("Name "+names[i]+"Phone Number "+phoneNumbers[i]+"Email id "+emails[i]);
                }
             }
             System.out.print("Enter name to search (Or <ENTER> if done): ");
             searchValue= scan.nextLine(); 
            }
    } //main()
} //class