End input of a string array

Question

I am trying to take input of an array of strings (each string is a question) and my code is as follows:

void read_quest()throws IOException
{
    System.out.println("enter the questions(enter null to end input operation)");
    for(int i = 0;; i++)
      {
        question[i]=in.readLine();
        if(question[i].equals("\0")==true)
        {
            n=i-1;
            break;
        }
    }
}

but the loop is never exited i am using bluej as it is for a school project(we are allowed to use only bluej) thanks in advance

score 4 · Answer 1 · edited May 23 '17 at 12:22

In Java, you don't have to deal with "\0". Also, it might be hard for the user to input NUL character anyway.

The method in.readLine() returns a String that was input by the user, excluding the end-of-line character that terminates it.

If you want to check if user presses Enter without entering any text, compare the input with the empty string "" like this:
if ("".equals(question[i]))
If you want to check for Ctrl+D (End of transmission character), compare with \4 as said in this post:
if ("\4".equals(question[i])).
Note: cannot test this in Eclipse, and the user will have to press Enter anyway after Ctrl+D

Note that if the user uses Ctrl-C, your readLine() will return null, and your program will exit not long after.

Side notes:

you don't need ==true, because x.equals(y) already is a boolean.
"literal".equals(variable) is safer than variable.equals("literal"): if your variable is null, the first version just yields false without crashing, while the second version throws NullPointerException.

score 3 · Answer 2 · answered Apr 29 '14 at 10:26

3

Compare it with anything other than "\0" and you are good to go, you have to do this because null cannot be entered

answered Apr 29 '14 at 10:26

Daksh Shah

2,997
6
37
71

score 1 · Answer 3 · answered Apr 29 '14 at 10:22

in.readLine() returns null if there are no more lines

void read_quest()throws IOException
{
    System.out.println("enter the questions(enter null to end input operation)");
    for(int i = 0;; i++)
      {
        question[i]=in.readLine();
        if(question[i]==null)
        {
            n=i-1;
            break;
        }
    }
}

score 1 · Answer 4 · answered Apr 29 '14 at 10:22

1

If the end of input, you can ask user just press enter without a string. so you can check for empty string or string length(0)

if (question[i].length() == 0) {
    break;
}

answered Apr 29 '14 at 10:22

Fizer Khan

88,237
28
143
153

score 0 · Answer 5 · answered Apr 29 '14 at 10:21

0

They cannot enter null - perhaps you meant a blank string? Try

if(question[i].equals(""))

answered Apr 29 '14 at 10:21

Evan Knowles

7,426
2
37
71

score 0 · Answer 6 · edited Apr 29 '14 at 11:46

0

in.readLine() is the method of inputstream it returns the line of text otherwise it returns the null so you have to check null condition.

if(question[i] == null)

Should solve your problem.

edited Apr 29 '14 at 11:46

J. Steen

15,470
15
56
63

answered Apr 29 '14 at 11:21

vikas patil

1
1

score 0 · Answer 7 · answered Apr 29 '14 at 11:55

0

You comparing the null in wrong way in Java, you need to change the if condition as follows:

if(question[i]==null)

answered Apr 29 '14 at 11:55

parag.rane

139
1
6

End input of a string array

7 Answers7