String.indexOf（）抛出StringIndexOutOfBoundsException

Question

在下面的程序中，我必须首先读取一个文件，然后再编写它。在运行配置中，我提供了文件的路径，但是当我运行程序时，它会给出错误：String index out of range: -1。 ？请帮忙

public static void main(String[] args) throws IOException{

String fileName = args[0];
    Scanner filescan;//to read the file
    filescan=new Scanner(new File(fileName));//read the whole file

FileWriter fstream = new FileWriter(fileName.subSequence(0,fileName.indexOf(".uniqe.ICext"))+".uniqe.Mpwm");
    BufferedWriter mpwm = new BufferedWriter(fstream);

Answer 1

你应该在使用substring之前添加验证。否则最终会抛出异常

int i= fileName.indexOf(".uniqe.ICext");
if(i<0)
    //file name can't substring or handle exception
else
    FileWriter fstream = new FileWriter(fileName.subSequence(0,i)+".uniqe.Mpwm");