Java Handling Exceptions

Java Catching and Handling Exceptions

  • You use the try, catch, and finally blocks — to write an exception handler.
    try, catch, and finally blocks example:
    ...
      public void writeList() {
        PrintWriter out = null;
        try {
          System.out.println("Entering >try statement");
          out = new PrintWriter(new FileWriter("OutFile.txt"));
          for (int i = 0; i < SIZE; i++) {
            out.println("Value at: " + i + " = " + vector.elementAt(i));
          }
        } catch (ArrayIndexOutOfBoundsException e) {
          System.err.println("Caught " +
                  "ArrayIndexOutOfBoundsException: " + e.getMessage());
        } catch (IOException e) {
          System.err.println("Caught IOException: " + e.getMessage());
        } finally {
          if (out != null) {
            System.out.println("Closing PrintWriter");
            out.close();
          } else {
            System.out.println("PrintWriter not open");
          }
        }
      }
    ...
  • Specifying the Exceptions Thrown by a Method (in this case an IOException):
    ...
      public void writeList() throws IOException {
        Vector vector = new Vector();
        PrintWriter out = new PrintWriter(new FileWriter("OutFile.txt"));
        for (int i = 0; i < 10; i++) {
          out.println("Value at: " + i + " = " + vector.elementAt(i));
        }
        out.close();
      }
    ...
  • When you make the methods throws an exception a calling method should handle the exception.
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