java - 在Java中将其添加和存储在数组中之前如何检查和输入？

Question

美好的一天..我有一个地址簿程序...它运行正常但它不检查用户输入是否已经存储在数组中..我想做的是......在获得用户之后输入将它与数组中存储的条目进行比较，当它是唯一的时……它将允许用户添加一个新条目……

这是我在 addEntry() 中的旧代码:

public void addEntry() {

entry[counter] = new AddressBookEntry();
entry[counter].setName(JOptionPane.showInputDialog("Enter name: "));
entry[counter].setAdd(JOptionPane.showInputDialog("Enter add: "));
entry[counter].setPhoneNo(JOptionPane.showInputDialog("Enter Phone No.: "));
entry[counter].setEmail(JOptionPane.showInputDialog("Enter E-mail: "));
counter++;

这是我打算做的，但结果是错误的:

public void addEntry() {

    entry[counter] = new AddressBookEntry();
    SName = JOptionPane.showInputDialog("Enter name: ");//<-- asks user for the name
    if (!entry[counter].getName().equals(SName)) {//<--compare
        entry[counter].setName(JOptionPane.showInputDialog("Enter name: "));
        entry[counter].setAdd(JOptionPane.showInputDialog("Enter add: "));
        entry[counter].setPhoneNo(JOptionPane.showInputDialog("Enter Phone No.: "));
        entry[counter].setEmail(JOptionPane.showInputDialog("Enter E-mail: "));
        counter++;
    }
}

这是错误:线程“main”中的异常 java.lang.NullPointerException 在 AddressBook.addEntry(AddressBook.java:57) 在 AddressBook.main(AddressBook.java:28)Java 结果:1构建成功(总时间:4 秒)

输出只要求用户输入一个名字然后自动退出...这可能是一个逻辑错误......但我不知道可能的解决方案是什么

需要帮助谢谢

这是我的完整代码:

import javax.swing.JOptionPane;
import javax.swing.JTextArea;

public class AddressBook {

    private AddressBookEntry entry[];
    private int counter;
    private String SName;
    private int notfound = 0;

    public static void main(String[] args) {
        AddressBook a = new AddressBook();
        a.entry = new AddressBookEntry[100];
        int option = 0;
        try {
            while (option != 5) {
                String content = "Choose an Option\n\n"
                        + "[1] Add an Entry\n"
                        + "[2] Delete an Entry\n"
                        + "[3] Update an Entry\n"
                        + "[4] View all Entries\n"
                        + "[5] View Specific Entry\n"
                        + "[6] Exit";
                option = Integer.parseInt(JOptionPane.showInputDialog(content));
                switch (option) {
                    case 1:
                        a.addEntry();
                        break;
                    case 2:
                        a.deleteEntry();
                        break;
                    case 3:
                        a.editEntry();
                        break;
                    case 4:
                        a.viewAll();
                        break;
                    case 5:
                        a.searchEntry();
                        break;
                    case 6:
                        System.exit(1);
                        break;
                    default:
                        JOptionPane.showMessageDialog(null, "Invalid Choice!");
                }
            }
        } catch (NumberFormatException e) {
            JOptionPane.showMessageDialog(null, "Please Choose a Number in the displayed Menu");
        }
    }

    public void addEntry() {
        entry[counter] = new AddressBookEntry();
        SName = JOptionPane.showInputDialog("Enter name: ");
        if (entry[counter] == null &&  entry[counter].getName() == null
                && !entry[counter].getName().equals(SName)) {
            entry[counter].setName(JOptionPane.showInputDialog("Enter name: "));
            entry[counter].setAdd(JOptionPane.showInputDialog("Enter add: "));
            entry[counter].setPhoneNo(JOptionPane.showInputDialog("Enter Phone No.: "));
            entry[counter].setEmail(JOptionPane.showInputDialog("Enter E-mail: "));
            counter++;
        }
    }
    /*public void addEntry() {
    entry[counter] = new AddressBookEntry();
    entry[counter].setName(JOptionPane.showInputDialog("Enter name: "));
    entry[counter].setAdd(JOptionPane.showInputDialog("Enter add: "));
    entry[counter].setPhoneNo(JOptionPane.showInputDialog("Enter Phone No.: "));
    entry[counter].setEmail(JOptionPane.showInputDialog("Enter E-mail: "));
    counter++;
    }*/

    public void viewAll() {
        String addText = "  NAME\tADDRESS\tPHONE NO.\tE-MAIL ADD\n\n";
        int nonNull = 0;
        for (int i = 0; i < entry.length; i++) {
            if (entry[i] != null) {
                addText = addText + entry[i].getInfo() + "\n";
                nonNull++;
            }
            if (nonNull == counter) {
                break;
            }
        }
        JOptionPane.showMessageDialog(null, new JTextArea(addText));
    }

    public void searchEntry() {
        SName = JOptionPane.showInputDialog("Enter Name to find: ");
        searchMethod();
    }

    public void searchMethod() {
        for (int i = 0; i < counter; i++) {
            if (entry[i].getName().equals(SName)) {
                JOptionPane.showMessageDialog(null, entry[i].getInfo2());
                notfound = 0;
                break;
            } else {
                notfound++;
            }
        }
        if (notfound != 0) {
            JOptionPane.showMessageDialog(null, "Name Not Found!");
        }
    }

    public void editEntry() {
        SName = JOptionPane.showInputDialog("Enter Name to edit: ");
        for (int i = 0; i < counter; i++) {
            if (entry[i].getName().equals(SName)) {
                entry[i] = new AddressBookEntry();
                entry[i].setName(JOptionPane.showInputDialog("Enter new name: "));
                entry[i].setAdd(JOptionPane.showInputDialog("Enter new add: "));
                entry[i].setPhoneNo(JOptionPane.showInputDialog("Enter new Phone No.: "));
                entry[i].setEmail(JOptionPane.showInputDialog("Enter new E-mail: "));
                notfound = 0;
                break;
            } else {
                notfound++;
            }
        }
        if (notfound != 0) {
            JOptionPane.showMessageDialog(null, "Name Not Found!");
        }
    }

    public void deleteEntry() {
        SName = JOptionPane.showInputDialog("Enter Name to delete: ");
        if (SName == null) {
            return;
        }
        for (int i = 0; i < counter; i++) {
            if (entry[i] != null && SName.equals(entry[i].getName())) {
                entry[i] = null;
                JOptionPane.showMessageDialog(null, "Found!");
                break;
            }
        }
    }
}

希望你能帮助我...因为我仍然不明白该怎么做。所以我只展示我的完整代码...感谢你们的耐心等待...

Answer 1

在尝试从中执行 getName() 之前，请检查以确保您的条目不为空。

if (!entry[counter].getName().equals(SName))

变成:

if  (entry[counter] != null 
 &&  entry[counter].getName() != null 
 && !entry[counter].getName().equals(SName))