java - 创建一个使用数组的自定义类

Question

我创建了一个类，它的对象是将帐号与帐号数组进行比较，并调用一个方法来返回一个数字是否有效。我收到以下编译器错误：program07.Program07.main(Program07.java:18) 的 program07.AccountVal.(AccountVal.java:12) 的线程“main”java.lang.NullPointerException 中的异常

这是我的课

package program07;


public class AccountVal
{
    private String[] accountNums;
    private String newAccount;

    public AccountVal()
    {
        accountNums[0] = "5658845";
        accountNums[1] = "8080152";
        accountNums[2] = "1005231";
        accountNums[3] = "4520125";
        accountNums[4] = "4562555";
        accountNums[5] = "6545231";
        accountNums[6] = "7895122";
        accountNums[7] = "5552012";
        accountNums[8] = "3852085";             
        accountNums[9] = "8777541";
        accountNums[10] = "5050552";
        accountNums[11] = "7576651";
        accountNums[12] = "8451277";
        accountNums[13] = "7825877";
        accountNums[14] = "7881200";
        accountNums[15] = "1302850";
        accountNums[16] = "1250255";
        accountNums[17] = "4581002";
        newAccount = "";
    }

    public void setAccountNums(String[] acc)
    {
        accountNums = acc;
    }

    public void setNewAccount(String newAcc)
    {
        newAccount = newAcc;
    }

    public String[] getAccountNums()
    {
        return accountNums;
    }

    public String getNewAccount()
    {
        return newAccount;
    }

    public boolean AccountValidation(String newAccount)
    {
        boolean test = false;

        for (int i = 0; i < 18; i++)
        {
            if(newAccount == accountNums[i])
            {
                test = true;
            }
        }
        return test;
    }
}

错误从程序中引用的行是我声明对象时：

AccountVal test = new AccountVal();

任何帮助将不胜感激。谢谢你！

Answer 1

NPE发生在这条线上

accountNums[0] = "5658845";

因为String数组accountNums尚未初始化。你可以这样做：

private String[] accountNums = new String[18];

---

或者，您可以声明您的数组，而不是使用数组大小​​和使用索引：

private String[] accountNums = { "5658845", "8080152", ... };

Answer 2

您永远不会初始化accountNums数组。你需要说：

private String[] accountNums = new String[18];