Question

I’m attempting to read the file.txt into java line by line and then when a line is “foo” I set the line after it to be “lineAfterFoo” then output that to the user.

My Java Code….

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

    try {
        FileReader someFile = new FileReader("file.txt");
        BufferedReader input = new BufferedReader(someFile);
        int i = 0;
        String[] line;
        line = new String[10];
        line[i] = input.readLine();

            while(line[i] != null) {

                line[i] = input.readLine();

                if (line[i] == "foo") {
                    i = i + 1;

                    line[i] = "lineAfterFoo";
                }

                i = i + 1;

            }

            for (int number = 1; number < i; number++) {
                System.out.println(line[number]);
            }

    } catch (FileNotFoundException e) {
        e.printStackTrace();

    }

}

File.txt

1
2
3
foo
HopeFullyThisWillChange
5
6
7
8
9
10

The Error…

java.lang.NoSuchMethodError: main
Exception in thread "main" 

Thanks for any help!

Answer 1

The main method must be static:

public static void main(String[] args) throws IOException {
    // snip...  
}

---

Edit – onto solving the real problem

The loop only runs once because, after the first pass through the while body, i will be equal to 1. At that point line[1] is null, because you haven’t read anything into it. Here’s the typical idiom used instead (note the changes in variable names):

int i = 0;
String line = null;
String[] lines = new String[10];

// read the next line and immediately check to see if it's null
// also make sure that i doesn't go out of range
while ((line = input.readLine()) != null
    && i < lines.length) {
    lines[i] = line;

    // Use .equals() (not ==) when comparing strings!
    if ("foo".equals(line)) {
        i++; // shorter form of i=i+1
        lines[i] = "lineAfterFoo";
    }
    i++;
}