Java buffered reader stops reading lines, if i add a if statement in the while loop:

Question

I am creating a game engine from scratch with java, i have started work on a new save file instead of using imaages for maps:

Works and prints out every line:

while ((readString = buf.readLine()) != null) {
    System.out.println("Failed to assign action to line: " + readString);
}

Doesnt work, prints out first 3 lines:

while ((readString = buf.readLine()) != null) {
                if (readString.contains("Width:")){
                    readString.replace("Width:", "");
                    readString.trim();
                    Integer.parseInt(readString);
                    System.out.println(readString);
                }else if (readString.contains("Height:")){
                    readString.replace("Height::", "");
                    readString.trim();
                    Integer.parseInt(readString);
                    System.out.println(readString);
                }else{
                    System.out.println("Failed to assign action to line: " + readString);
                }
}

As you can see, the top one is working and prints out every line to the console, the second one stops after reading the 3rd line. I haven't found anything while researching the problem, and my syntax appears to be correct. What's wrong with my code?

Please read http://stackoverflow.com/editing-help to see how to include code in questions. It's really not great for the code to be on a different site. — Jon Skeet, Jan 05 '14 at 20:31
My guess is that an exception is being thrown - possibly by Integer.parseInt - but that maybe you're swallowing it. — Jon Skeet, Jan 05 '14 at 20:32
Another thing to try would be to copy the String before calling methods on it (and then calling those methods on the copy), though it *should* not make a difference. — SirRichie, Jan 05 '14 at 20:34

score 5 · Answer 1 · edited Jan 07 '14 at 23:12

5

There probably is an exception that you are not seeing.

Put this around your code:

try {
   //.. your while-loop here
}
catch(Exception e) {
   e.printStackTrace();
}

Then fix the error.

Another hint: readString.replace("Width:", ""), readString.trim() and Integer.parseInt(readString) won't work. The functions don't change the variable itself, you need to assign their results to a variable.

Example:

 readString = readString.trim();

edited Jan 07 '14 at 23:12

Farce

175
2
8

answered Jan 05 '14 at 20:36

JayL

574
5
18

Although it's probably better practice to store the string in another variable rather than change the initial value. – JamoBox Jan 05 '14 at 20:38
Ok thank you people, @JamoBox i would but theres no point, when im not doing anything to the line other than reading it in to set variables – user3163393 Jan 05 '14 at 20:50
Hence the use of the phrase "better practice" – JamoBox Jan 05 '14 at 21:05

Roger Lindsjö · Accepted Answer · 2014-01-06T14:00:48.410

There is probably an exception that you are swallowing (catching and ignoring) un your program and this is the most probable candidates:

Strings are immutable so when you replace / trim the original string is the same, and a new one is returned.

} else if (readString.contains("Height:")){
    readString.replace("Height::", "");
    readString.trim();
    Integer.parseInt(readString);

Here you ignore the returned (new) strings and keep operating on the original string. Also, as you can see you check for Height: and the you remove Height:: (notice the double colon). So, unless your data actually contains Height:: the Height: will be left in the string when calling Integer.parseInt this causing an exception.

It should be more like this

} else if (readString.contains("Height:")){
    readString = readString.replace("Height:", "");
    readString = readString.trim();
    Integer.parseInt(readString);

Java buffered reader stops reading lines, if i add a if statement in the while loop:

2 Answers2