charAt()调用中的StringIndexOutOfBoundsException

Question

我是编程新手，我正在尝试编写一个匹配两个文本文件的程序。对于第一行，我匹配第一个字符，第二行匹配两个字符，依此类推，直到其中一个文件结束。

这是问题所在。如果该行没有足够的字符，则只比较存在的字符，如果两行99都有"abc"，则将其视为匹配。

我似乎无法在不抛出错误的情况下满足这个要求，因为如果字符数少于行数，charAt()将读取null。谢谢你的帮助！

代码：

public static void main(String[] args) throws IOException
{
    boolean flag;
    File f = new File(args[0]);
    Scanner sc = new Scanner(f);
    File f2 = new File(args[1]);
    Scanner sc2 = new Scanner(f2);
    int line = 1;
    String t1 = "";
    String t2 = "";
    String work = "";

    while(sc.hasNext() && sc2.hasNext())
    {
        String line1 = sc.nextLine().toUpperCase();
        String line2 = sc2.nextLine().toUpperCase();
        line1 = line1.trim();
        line2 = line2.trim();
        for(int i = 0; i < line; i++)
        {
            if(line1.charAt(i) != line2.charAt(i))
            {
                work = "no";
                t1 = Character.toString(line1.charAt(i));
                t2 = Character.toString(line2.charAt(i));
            }
            else
            {
                work = "";
                t1 = Character.toString(line1.charAt(i));
                t2 = Character.toString(line2.charAt(i));
            }
        }
        if(work == "")
        {
            System.out.println("Line # " + line + ": Matching " + line + " character/s true " + "**" + line1 + "**" + " and " + "**" + line1 + "**");

        }
        else
        {
            System.out.println("Line # " + line + ": Matching " + line + " character/s false " + "**" + line1 + "**" + " and " + "**" + line2 + "**");
        }
        line += 1;
    }
}

Answer 1

您需要检查line1和line2的长度与i变量的长度，然后在该行最后一个字母的末尾调用char。

类似于if(line1.length() < i)

String.length()

Answer 2

1.检查两行的长度是否相等，如下所示(并将变量work改为boolean而不是String)。这有助于提高性能，因为boolean占用1个字节，而String占用的字节更多。

if (line1.length() > line2.length()) {
    work = false;
} else if (line1.length() < line2.length()) {
    work = false;
} else if (line1.charAt(i) != line2.charAt(i)) {
    work = false;
} else {
    work = true;
}

或者：

if (line1.length() != line2.length()) {
    work = false;
} else {
    work = true;
}

或者：

if (line1.length() == line2.length()) {
    work = true;
} else {
    work = false;
}

然后

if(work) {//This is the same as if (work == true)
    System.out.println("Line # " + line + ": Matching " + line + " character/s true " + "**" + line1 + "**" + " and " + "**" + line1 + "**");
} else {
    System.out.println("Line # " + line + ": Matching " + line + " character/s false " + "**" + line1 + "**" + " and " + "**" + line2 + "**");
}

但是，如果你真的想/需要使用work变量作为String，那么不要将其与==进行比较，而是与work.equals("")或"".equals(work) (第二个变量阻止了NullPointerException )进行比较。

阅读有关.equals()、Java == vs equals()和How do I compare Strings in Java的更多信息。关于"".equals(variable) vs variable.equals("")

此外，如果在任何位置这两行在任何字母处都不匹配，您可能想要break或continue您的循环。