StringIndexOutOfBoundsException: String index out of range: 0 while reading a file

Question

I have a simple program which reads a file. Now there is a blank space in between the line. I get the StringIndexOutOfBoundsException: String index out of range: 0 error there. Please help

class main{
    public static void main(String args[]) {
       String str;
        try {
    BufferedReader br = new BufferedReader ( new FileReader("train.txt"));
    while((str=br.readLine())!=null){ 
    System.out.println(str);
    int a=str.charAt(0);

    if(str.trim().length()==0){
        System.out.println("stupid");
    }
    else if(a==32){
        System.out.println("ddddd");
    }

    else if(str.charAt(0)=='A' ||str.charAt(0)=='a'){
        System.out.println("hahha");
    }
    else if(str.charAt(0)=='C' ||str.charAt(0)=='c'){
        System.out.println("lol");
    }

    else if(str.charAt(0)=='D' ||str.charAt(0)=='d'){
        System.out.println("rofl");
    }
    else{
    System.out.println("blank");
    }


}
        }
catch (FileNotFoundException e){
    System.out.println(e);
}
catch (IOException e){
    System.out.println(e);
}
    }

Answer 1

If a line is blank, there is no character at index 0 since the string is empty. You are executing this line:

int a=str.charAt(0);

before testing whether the line is blank. There are several possible solutions. One is to reorganize your code like this:

if(str.trim().length()==0){
    System.out.println("stupid");
    continue; // so rest of loop body is skipped
}
int a=str.charAt(0);
if(a==32){
    System.out.println("ddddd");
}

Answer 2

The line below will throw a StringIndexOutOfBoundsException when it reads an empty line.

int a=str.charAt(0);

Replace it with:

if(str.trim().length()>0)
a=str.charAt(0);