When using recursion method returns 0

Question

I have the following code:

public int lerInt() {
    String entrada = "";
    int saida = 0;
    try {
        entrada = input.readLine();
    } catch (IOException e) {
        System.out.println("Falha critica.");
    }
    try {
        saida = Integer.parseInt(entrada);
    } catch (NumberFormatException e) {
        System.out.println("Você digitou uma entrada invalida.");
        lerInt();
    }
    return saida;
}

Assuming the user typed something with letter, it would fall into NumberFormatException and would have to type again. However, on the second attempt the method returns 0, regardless of the number it enters.

I needed it to run until the user entered something valid, and I don’t know why it’s returning 0.

Answer 1

There are some problems in your code.

I created the variable input There in the same method, you must have created elsewhere. There may even be some reason you did this, but I think within the method is the best place to declare this variable. I see no point in creating something outside of it that seems to be used only within it. Better use the scope.

There were unnecessary variables. The code is simpler. The only thing you needed to do was try to return a converted integer value of the characters read on the keyboard.

If this attempt fails she will try to perform some catch. Not necessarily these two listed there, could be some other catch in the call stack its implementation (including the catch hidden that every Java application has to protect your application from any untreated exceptions).

Normally you only use a single block of try in these situations. You put how many catches are necessary to give the correct treatment for every mistake you know how to treat.

If you give one of these two problems indicated by your code instead of returning the result, before completing the return He will divert to one of the blocks that know how to treat the problem. In case both just show the custom message indicating to the user what went wrong.

How this is inside a loop the whole process will be tried again. By the time everything went right the return is executed to the end without a diversion to a catch, then the method is finished with the appropriate result.

This while is called loop infinite. It will run until it is true and I am saying it is true always. Even though it is infinite, of course there is a way to escape it, which in this case is the return.

I made it a little different:

public int lerInt() {
    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
    while (true) {
        try {
            return Integer.parseInt(input.readLine());
        } catch (IOException e) {
            System.out.println("Falha critica.");
        } catch (NumberFormatException e) {
            System.out.println("Você digitou uma entrada invalida.");
        }
    }
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

Note that your attempt to recur the method lerInt() can cause stack overflow problems in extreme cases of many invalid data. Rarely recursion is the solution.

That question should interest you. She explains better about the use of return before a finally which is practically the same thing as a catch.