• Exceptions are Objects thrown when a problem occurs with your program
  
• An Exception trace shows where the exception happened
  

• Exceptions can be caught by any of the methods in the call stack.
• If nothing catches the Exception, the program terminates

 public class ExceptionDemo {
     public static void main(String[] args) {
          handleArgs(args);
     }
     public static void handleArgs(String[] args) {
          if(args.length == 0)
               throw new RuntimeException("Must pass an argument to the 
               function.");
          if(args[0].length() <= 1) 
               throw new RuntimeException("Argument must be at least 2 
               characters.");
     }
}

 public static void main(String[] args) {
     try {
          handleArgs(args);
     } catch (Exception e) {
          System.out.println(e.getMessage());
     }
}

• Exception (checked)
  
• An expected condition that the program will handle
• Derived from java.lang.Exception
• Must be declared up the call-stack, until it is handled
• IOException is a checked exception

• RuntimeException (unchecked)
• Not an expected situation
• Derived from java.lang.RuntimeException
• Does not need to be declared on the methods in the call stack.
• NumberFormatException is a RuntimeException

public static void main (String[] args) throws Exception {
     try {
          handleArgs(args);
     } finally {
          System.out.println("We handled args");
     }
}

public static void fileRead (File file) throws Exception {
     Reader in = null;
     try {
          in = new InputStreamReader(new FileInputStream("test.txt"));
          System.out.println(in.read());
     } finally {
          if (in != null) {
               in.close();
          }
     }
}

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• Exceptions