Java, while loop with scanner inside and as a statement

Question

Trying to run the while loop for a password check. I do keep getting an error that the variable haslo cannot be found. Tried declaring it outside the loop - then it says, it's already declared. I know it can be done with infinite loop and the break command. Just curious whether it's possible this way.

String password = "pw123";

while (!haslo.equals(password)){

        System.out.println("Enter pw:");
        String haslo = reader.nextLine();

        if (haslo.equals(password))
            System.out.println("Right!");

        else
            System.out.println("Wrong!");
}

"Tried declaring it outside the loop" <- That was the right way. Declare it once, then just update the value inside the loop: haslo = reader.nextLine(); — user6073886
– user6073886, Commented Sep 18, 2017 at 15:46
cos you are trying to read the value of haslo before it is declared... — ΦXocę 웃 Пepeúpa ツ
– ΦXocę 웃 Пepeúpa ツ, Commented Sep 18, 2017 at 15:46
side bar: the loop must be executed at least once. Consider changing to a do-while loop. — Andrew S
– Andrew S, Commented Sep 18, 2017 at 15:53

VHS · Accepted Answer · 2017-09-18 15:57:56Z

2

Declare the variable haslo as String haslo = ""; before the loop starts.
In the loop, replace your line String haslo = reader.nextLine(); with haslo = reader.nextLine();.

Reasoning:

For 1 --> Your while loop is referencing the variable haslo before it is declared. So you need to declare it before it is referenced.

For 2 --> Once it is declared, you don't want to re-declare it because the one declared before the loop is already made available within the scope of the loop.

answered Sep 18, 2017 at 15:57

VHS

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Comments

Sweeper · Accepted Answer · 2017-09-18 15:46:45Z

0

This is all about scopes.

Your haslo variable is declared inside the while loop and so can only be used inside it, after he declaration. The condition of the while loop is evaluated before the declaration of haslo so you can't use haslo there.

To fix this, declare haslo outside the while loop:

String haslo = "";
while (!haslo.equals(password)){

    System.out.println("Enter pw:");
    haslo = reader.nextLine(); // <-- note that I did not write "String" here because that will declare *another* variable called haslo.

    if (haslo.equals(password))
        System.out.println("Right!");

    else
        System.out.println("Wrong!");
}

answered Sep 18, 2017 at 15:46

Sweeper

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Comments

derOtterDieb · Accepted Answer · 2017-09-18 15:46:53Z

0

Can you try something like this ? You need to declare haslo before the loop, then you can use it inside the loop, and avoid the infinite loop.

String password = "pw123";
String haslo = "";

while (!haslo.equals(password)){

    System.out.println("Enter pw:");
    haslo = reader.nextLine();

    if (haslo.equals(password))
        System.out.println("Right!");

    else
        System.out.println("Wrong!");

}

answered Sep 18, 2017 at 15:46

derOtterDieb

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Comments

JustinKSU · Accepted Answer · 2017-09-18 15:54:01Z

0

The problem can be found by following it step by step:

String password = "pw123"; (Good)

while (!haslo.equals(password)){ (Bad. What is Haslo? It is not defined before you use it here)

Try this:

String password = "pw123";
String haslo = "";
while (!haslo.equals(password)){
    System.out.println("Enter pw:");
    haslo = reader.nextLine();

    if (haslo.equals(password))
        System.out.println("Right!");

    else
        System.out.println("Wrong!");

}

edited Sep 18, 2017 at 15:54

JustinKSU

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answered Sep 18, 2017 at 15:48

J. Tate

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Comments

Ella · Accepted Answer · 2017-09-18 15:55:36Z

0

Declare String INSIDE loop again! otherwise next time loop will not work! you gave it a reference, but loop needs to know what the reference is again.

answered Sep 18, 2017 at 15:55

Ella

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