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"the variable may not have been initialized" although I'm pretty sure it is

I am having problems with Javac while compiling this piece of code:

public static int getYear() {
    Console input = System.console();
    Boolean gotYear = false;
    int year;

    String userInput = input.readLine();

    while (!gotYear) {
        try {
            year = Integer.parseInt(userInput);
            gotYear = true;
        } catch (Exception e) {
            System.out.print("Please insert a valid date. ");
            userInput = input.readLine();
        }
    }

    return year;
}

Javac is giving me an error on the line return year;

that "the variable" year "may not have been initialized". But since it is inside a while loop, I know for sure that it will be initialized. I asked T. about this and he could not answer me why this is happening. His best guess is that Javac is not a very good compiler for understanding what it is.

Basically why is this error happening? I know I can fix this by initializing the year before I step into the while loop, but I wanted to know if there is another way to achieve what I am trying to achieve.

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6 answers


Your year variable is initialized in a try block. It's obvious to us that it won't exit the loop until something OK is entered. But the compiler rules are simpler than that: since the initialization can be violated except, it thinks that the year can be uninitialized.



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Not. You must initialize. Method method local variables must be initialized before being used.



The local variable will not receive default values. You must initialize them before using them.

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Imagine a situation where gotYear in

while (!gotYear)

evaluates to true .

In this case, year will not be initialized as it is inside a while loop.

while (!gotYear) {
    try {
        year = Integer.parseInt(userInput);
        gotYear = true;
    } catch (Exception e) {
        System.out.print("Please insert a valid date. ");
        userInput = input.readLine();
    }
}

At compile time, the java compiler does not evaluate expressions. Therefore gotYear can take one of two values true or false .

Local variables must be initialized in the same scope in which they are declared. Internalization should be done before using it.

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You must initialize local variables. Go through This to understand the basics

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Local variables are used primarily for intermediate calculations, while instance variables are supposed to carry data for calculations for both the future and the intermediate. Java allows default values ​​for instance variables, but local variables need to be assigned a value. Therefore, to avoid errors, you need to initialize local variables.

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year

will not be assigned when it Integer.parseInt(userInput);

throws a NumberFormatException.

What gotYear

then remains a boolean .FALSE while storing in a loop is too complicated for the compiler. He thinks that you will somehow get out of the loop.

The following should behave better.

for (;;) {
    try {
        year = Integer.parseInt(userInput);
        break;
    } catch (Exception e) {
        System.out.print("Please insert a valid date. ");
        userInput = input.readLine();
    }
}

Perhaps the compiler can simply accept:

for (boolean keepAsking = true; keepAsking; ) {
    try {
        year = Integer.parseInt(userInput);
        keepAsking = false;

BTW is better to use boolean

instead of object wrapper class boolean

.

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