Responding to Abnormal Conditions

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Chapter 17
Responding to Abnormal Conditions

   17.1 Background
   17.2 Exception Catching
   17.3 Exception Forwarding
   17.4 Assignment #22: Exceptions

17.1 Background

An exception is a representation of an error or an unexpected condition.
Exceptions are notified by objects of special exception classes.

class prg {
  public static void main ( String [] args ){
    int i = 1;
    i = i / 0;
} }

// Run time error:
//   Exception in thread "main" java.lang.ArithmeticException: / by zero
//      at prg.main(a.java:4)

17.2 Exception Catching

The exception conditions can be handled by try/catch blocks:
try { <code>  }
catch ( <exception parameter> ) { <respond> }
..........
catch ( <exception parameter> ) { <respond> }

try {  i = 1 / 0;  }
catch (java.lang.ArithmeticException ae){
    System.out.println( "error: division by 0" );
}
An abnormal termination of the try block transfers the control out with an object of the exception type.
The first catch fragment, having the parameter type of the exception object, is executed.

17.3 Exception Forwarding

Constructors and methods may request the forwarding of uncaught exceptions upward to the calling points. Such requests are made by including a clause of the following form in the interface, immediately after the parameter list.
throws <exception type>

class prg {
   public static void main (String [] args) {
     int i;
     try{  i = getInt( "abc" );  }
     catch (java.lang.NumberFormatException e ){
       System.out.println( "Warning: improper argument!" );
     }
   }
   static int getInt( String s )
                      throws java.lang.NumberFormatException {
          return  Integer.parseInt( s );
   }
}
The constructors and methods should catch or forward all the exceptions not under the ‘java.lang.RuntimeException’ and ‘java.lang.Error’ subtrees of classes.

Exercises

17.4 Assignment #22: Exceptions

Due: skip

The given program uses a single-parameter method ‘repoertType’ that, when provided an argument of type String, reports whether or not the argument can be parsed to a value of type byte.

Modify the ‘reportType’ method so that it will report for each primitive numeric type whether or not the argument can be parsed to a value of that type.

The program should provide an output of the following form.

   byte short     int         long          float                 double
123
    123   123     123          123          123.0                  123.0
1234
     no  1234    1234         1234         1234.0                 1234.0
123456
     no    no  123456       123456       123456.0               123456.0
12345678901
     no    no      no  12345678901  1.23456788E10        1.2345678901E10
12345678901234567890
     no    no      no           no   1.2345679E19  1.2345678901234567E19
1.2e34
     no    no      no           no         1.2E34                 1.2E34
1.2e123
     no    no      no           no       Infinity                1.2E123
1.2e345
     no    no      no           no       Infinity               Infinity
abc
     no    no      no           no             no                     no

lab22.java
class lab22 {
    public static void main (String [] args) {
      print( "byte", 7 );    print( "short", 6  );    print( "int", 8  );
      print( "long", 13 );   print( "float", 15 );    print( "double", 23 );
      System.out.println();
      reportType("123");
      reportType("1234");
      reportType("123456");
      reportType("12345678901");
      reportType("12345678901234567890");
      reportType("1.2e34");
      reportType("1.2e123");
      reportType("1.2e345");
      reportType("abc");
    }
    static void reportType( String s ){

      System.out.println( s );

      try{ byte bb = Byte.parseByte( s );
         print( "" + bb, 7 );
      }  catch( java.lang.NumberFormatException be ){
         print( "no", 7 );
      }

      System.out.println();

   }
   static void print ( String s, int n){
     String f = s;
     int i;
     for( i=0; i<n; i++ ){ f = " " + f; }
     i = f.length();
     f = f.substring( i-n );
     System.out.print( f );
   }
}

Assume ‘lab22’ for the submit program, and submit the lab22.java file.

Note: Files that fail to compile, and execute when applicable, will not be examined. They will be awarded a grade of 0 points.

[next] [prev] [prev-tail] [front] [up] [toc]

Chapter 17Responding to Abnormal Conditions

17.1 Background

17.2 Exception Catching

17.3 Exception Forwarding

17.4 Assignment #22: Exceptions

Chapter 17
Responding to Abnormal Conditions