Java Try and Catch IOException Problem

Question

I am trying to use a bit of code I found at the bottom of this page   Here is the code in a class that I created for it   import java io LineNumberReader  import java io FileReader  import java io IOException   public class LineCounter     public static int countLines String filename  throws IOException       LineNumberReader reader    new LineNumberReader new FileReader filename        int cnt   0      String lineRead           while   lineRead   reader readLine       null         cnt   reader getLineNumber        reader close        return cnt          My objective is to count the lines of a text file  store that number as an integer  then use that integer in my main class   In my main class I tried a few different ways of making this happen  but  being a new programmer  I am missing something   Here is the first thing I tried   String sFileName    MyTextFile txt   private int lineCount   LineCounter countLines sFileName     With this attempt I get the error  unreported exception java io IOException  must be caught or declared to be thrown    I don t understand why I am getting this because as I can see the exception is declared in my  countLines  method   I tried to use a try catch block right under that last bit of code I posted  but that didn t work either  I don t think I did it right though    Here is my try catch attempt   String sFileName    MyTextFile txt   private int lineCount       try          LineCounter countLines sFileName             catch IOException ex           System out println  ex toString             System out println  Could not find file     sFileName             Please show me the way   Thanks in advance for your help

User · Accepted Answer

Initializer block is just like any bits of code; it's not "attached" to any field/method preceding it. To assign values to fields, you have to explicitly use the field as the lhs of an assignment statement.

private int lineCount; {
    try{
        lineCount = LineCounter.countLines(sFileName);
        /*^^^^^^^*/
    }
    catch(IOException ex){
        System.out.println (ex.toString());
        System.out.println("Could not find file " + sFileName);
    }
}

Also, your countLines can be made simpler:

  public static int countLines(String filename) throws IOException {
    LineNumberReader reader  = new LineNumberReader(new FileReader(filename));
    while (reader.readLine() != null) {}
    reader.close();
    return reader.getLineNumber();
  }

Based on my test, it looks like you can getLineNumber() after close().

User · Answer

The reason you are getting the the IOException is because you are not catching the IOException of your countLines method   You ll want to do something like this   public static void main String   args      int lines   0          TODO - Need to get the filename to populate sFileName   Could      come from the command line arguments      try          lines   LineCounter countLines sFileName             catch IOException ex           System out println  ex toString             System out println  Could not find file     sFileName             if lines  gt  0            Do rest of program

User · Answer

Your countLines String filename  method throws IOException   You can t use it in a member declaration  You ll need to perform the operation in a main String   args  method   Your main String   args  method will get the IOException thrown to it by countLines and it will need to handle or declare it   Try this to just throw the IOException from main  public class MyClass     private int lineCount    public static void main String   args  throws IOException       lineCount   LineCounter countLines sFileName           or this to handle it and wrap it in an unchecked IllegalArgumentException   public class MyClass     private int lineCount    private String sFileName     myfile     public static void main String   args  throws IOException       try         lineCount   LineCounter countLines sFileName          catch  IOException e           throw new IllegalArgumentException  Unable to load     sFileName  e

[java] Java Try and Catch IOException Problem

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