Unreachable code when closing scanner in java?

Question

When I try to close myScanner I get a red line under myScanner.close telling me it is unreachable code. What am I doing wrong?

public class crypt {    

static final char FIRST = ' ';
static final char LAST = ']';

static final int RANGE = LAST-FIRST+1;

public static void main(String[] args) {
    safe("");

}

public static boolean safe(String word) {
    Scanner myScanner = new Scanner(System.in);
    word = myScanner.nextLine();
    String upper = word.toUpperCase();
        for (int i=0; i<upper.length(); i++) {
            char c = upper.charAt(i);
                if (c < FIRST && c > LAST) {
                    return true;
                }
        }
    return false;
    myScanner.close();
}

Did you have a look at what is present in the line above ```myScanner.close();``` ? — kkaosninja, Oct 05 '16 at 21:02
That line is indeed unreachable, because you will never reach it - you `return` from the function first. — David T. Macknet, Oct 05 '16 at 21:37
You don't really need to use `Scanner.close()` anymore, right? — RobotKarel314, Oct 05 '16 at 23:25

score 0 · Answer 1 · answered Oct 05 '16 at 21:01

This line :

return false;

stop the function to return the result "false", so the code after this statement will not be executed.

Also, you should close your scanner after using it, so first move the

myScanner.close();

statement BEFORE "return false;", and also add it before the "return true;" statement.

score 0 · Answer 2 · answered Oct 05 '16 at 21:04

0

Once the return statement is called, the next line will not get executed and this causes the compilation error.

answered Oct 05 '16 at 21:04

HARDI

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5
12

Speerian · Accepted Answer · 2016-10-05T21:25:20.780

You'll want to move myScanner.close(); to the line before 'return false;'. Another thing to note - you aren't closing the scanner when you return true. You may want to add myScanner.close(); in front of return true;.

public static boolean safeToUse(String plaintext) {
    Scanner myScanner = new Scanner(System.in);
    plaintext = myScanner.nextLine();
    String upper = plaintext.toUpperCase();
        for (int i=0; i<upper.length(); i++) {
            char c = upper.charAt(i);
                if (c < FIRST && c > LAST) {
                    myScanner.close(); //Close the scanner before you return true
                    return true;
                }
        }
    myScanner.close(); //close the scanner before you return.
    return false;
}

When you are inside a function, code will not be executed after you return. Think of return as marking a stopping point in your code. When it reaches this point it will go to where that method/function(safeToUse() in your case) was called.

A good way of tracking and better understanding the execution of the code it to step through your program, although you'll have to make the suggested changes first to get it to compile.

Unreachable code when closing scanner in java?

3 Answers3