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Example with and without exception handling
this example from a Well House Consultants training course
Source code: Xena.java Module: J050
public class Xena {
// Following works well but ONLY if run correctly! // (Name changed to ensure it doesn't get run!) public static void main_copy (String [] args) { for (int k=0; k<4; k+=2) { int retire = 65 - Integer.parseInt(args[k+1]); System.out.println(args[k] + " can retire in "+retire+" years"); } } /* LOOKS GOOD: Dorothy-2:java grahamellis$ java Xena Bob 23 Roberta 26 Bob can retire in 42 years Roberta can retire in 39 years Dorothy-2:java grahamellis$ MAGNIFICENT FAILURES: Dorothy-2:java grahamellis$ java Xena 23 John 16 Willy Exception in thread "main" java.lang.NumberFormatException: For input string: "John" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48) at java.lang.Integer.parseInt(Integer.java:447) at java.lang.Integer.parseInt(Integer.java:497) at Xena.main(Xena.java:4) Dorothy-2:java grahamellis$ AND ANOTHER: Dorothy-2:java grahamellis$ java Xena Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1 at Xena.main(Xena.java:4) Dorothy-2:java grahamellis$ */ /* Let's try that but catch the exceptions! */ /* Capture run time errors (exceptions). The order of the catch blocks is important! Whichever is catched first is the one it takes. Nesting is also important; try within for will allow loop to run around again, but for within try would exit the whole loop is an exception is caught! */ public static void main (String [] args) { for (int k=0; k<4; k+=2) { int retire = 999; try { retire = 65 - Integer.parseInt(args[k+1]); } catch (ArrayIndexOutOfBoundsException e) { System.out.println("I've run out of data"); break; } catch (NumberFormatException anything) { System.out.println("Wanted no.; got str\n" + anything); retire = 50; // Assume whole working life! } catch (Exception e) { System.out.println("Summat else failed"); break; } System.out.println(args[k] + " can retire in "+retire+" years"); } } /* Demo does NOT show "finally" block, nor an exception being thrown up to the calling code. */ } Learn about this subject
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