Exception-Handling Overview

Size: px
Start display at page:

Download "Exception-Handling Overview"

Transcription

1 م.عبد الغني أبوجبل Exception Handling No matter how good a programmer you are, you cannot control everything. Things can go wrong. Very wrong. When you write a risky method, you need code to handle the bad things that might happen. Exception-Handling Overview An exception is a runtime error. A program that does not provide code for catching and handling exceptions will terminate abnormally, and may cause serious problems. For example, if your program attempts to transfer money from a savings account to a checking account, but because of a runtime error is terminated after the money is drawn from the savings account and before the money is deposited in the checking account, the customer will lose money. Exceptions occur for various reasons. The user may enter an invalid input, or the program may attempt to open a file that doesn't exist, or the network connection may hang up, or the program may attempt to access an outof-bounds array element. You have already been briefly introduced to exceptions in earlier chapters. you learned that an ArrayIndexOutOfBoundsException occurs if you access an element past the end of an array. you learned that a NullPointerException occurs when you invoke a method on a reference variable with null value. you learned that a StringIndexOutOfBoundsException occurs when you access a character in a string using an out-of-bound index. When an exception occurs, the normal execution flow of the program will be interrupted. Java provides programmers with the capability to handle runtime exceptions. With this capability, referred to as exception handling, you can develop robust programs for mission-critical computing. Example Page 1

2 م.عبد الغني أبوجبل The program above will terminate abnormally if you enter a floating-point value instead of an integer. Note that several lines of information are displayed above in response to this invalid input. This information, known as the stack trace, includes the name of the exception (java.util.inputmismatchexception) followed by the method call stack at the time the exception occurred. The stack trace helps in debugging a program. Starting from the last line of the stack trace, you see that the exception was detected in line 7 of the main method. Each line of the stack trace contains the class name and method (ExceptionDemo.main) along with the file name and line number (ExceptionDemo.java: 7). Moving up the stack trace, you see that the exception occurred in line 2000 in the nextint method of the Scanner class, the exception occurred in line 2040 in the overloaded nextint method of the Scanner class, the exception occurred in line 1431 in the next method of the Scanner class, the exception occurred in line 819 in the throwfor method of the Scanner class. The last method in the call chain actually threw an InputMismatchException. The try Block The first step in constructing an exception handler is to enclose the code that might throw an exception within a try block. In general, a try block looks like the following: try { code catch and finally blocks... To construct an exception handler for the main method from the ExceptionDemo class, enclose the exception-throwing statements of the main method within a try block. There is more than one way to do this. You can put each line of code that might throw an exception within its own try block and provide separate exception handlers for each. Or, you can put all the code within a single try block and associate multiple handlers with it. The following listing uses one try block for the entire method because the code in question is very short. Page 2

3 م.عبد الغني أبوجبل If an exception occurs within the try block, that exception is handled by an exception handler associated with it. To associate an exception handler with a try block, you must put a catch block after it. The catch Blocks You associate exception handlers with a try block by providing one or more catch blocks directly after the try block. No code can be between the end of the try block and the beginning of the first catch block. try { catch (ExceptionType name) { catch (ExceptionType name) { Each catch block is an exception handler and handles the type of exception indicated by its argument. The argument type, ExceptionType, declares the type of exception that the handler can handle and must be the name of a class that inherits from the Throwable class. The handler can refer to the exception with name. The catch block contains code that is executed if and when the exception handler is invoked. The runtime system invokes the exception handler when the handler is the first one in the call stack whose ExceptionType matches the type of the exception thrown. The system considers it a match if the thrown object can legally be assigned to the exception handler's argument. Page 3

4 م.عبد الغني أبوجبل The finally Block The finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. Exception Types RuntimeException, Error, and their subclasses are known as unchecked exceptions. All other exceptions are known as checked exceptions, meaning that the compiler forces the programmer to check and deal with them. Declaring Exceptions Every method must state the types of checked exceptions it might throw. This is known as declaring exceptions. Because system errors and runtime errors can happen to any code, Java does not require that you declare Error and RuntimeException (unchecked exceptions) explicitly in the method. However, all other exceptions thrown by the method must be explicitly declared in the method declaration so that the caller of the method is informed of the exception. Page 4

5 م.عبد الغني أبوجبل To declare an exception in a method, use the throws keyword in the method declaration, as in this example: public void mymethod() throws IOException The throws keyword indicates that mymethod might throw an IOException. If the method might throw multiple exceptions, add a list of the exceptions, separated by commas, after throws: public void mymethod() throws Exception1, Exception2,..., ExceptionN If a method does not declare exceptions in the superclass, you cannot override it to declare exceptions in the subclass. Throwing Exceptions A program that detects an error can create an instance of an appropriate exception type and throw it. This is known as throwing an exception. Here is an example: Suppose the program detected that an argument passed to the method violates the method contract (e.g., the argument must be non-negative, but a negative argument is passed); the program can create an instance of IllegalArgumentException and throw it, as follows: IllegalArgumentException ex = new IllegalArgumentException("Wrong Argument"); throw ex; Or if you prefer, you can use the following: throw new IllegalArgumentException("Wrong Argument"); The keyword to declare an exception is throws, and the keyword to throw an exception is throw Catching Exceptions You now know how to declare an exception and how to throw an exception. When an exception is thrown, it can be caught and handled in a try-catch block, as follows: try { statements; // Statements that may throw exceptions catch (Exception1 exvar1) { handler for exception1; catch (Exception2 exvar2) { handler for exception2;... catch (ExceptionN exvar3) { handler for exceptionn; Page 5

6 م.عبد الغني أبوجبل If no exceptions arise during the execution of the try block, the catch blocks are skipped. If one of the statements inside the try block throws an exception, Java skips the remaining statements in the try block and starts the process of finding the code to handle the exception. The code that handles the exception is called the exception handler; it is found by propagating the exception backward through a chain of method calls, starting from the current method. Each catch block is examined in turn, from first to last, to see whether the type of the exception object is an instance of the exception class in the catch block. If so, the exception object is assigned to the variable declared and the code in the catch block is executed. If no handler is found, Java exits this method, passes the exception to the method that invoked the method, and continues the same process to find a handler. If no handler is found in the chain of methods being invoked, the program terminates and prints an error message on the console. The process of finding a handler is called catching an exception. Suppose the main method invokes method1, method1 invokes method2, method2 invokes method3, and an exception occurs in method3, as shown in figure below Consider the following scenario: If method3 cannot handle the exception, method3 is aborted and the control is returned to method2. If the exception type is Exception3, it is caught by the catch block for handling exception ex3 in method2. statement5 is skipped, and statement6 is executed. If the exception type is Exception2, method2 is aborted, the control is returned to method1, and the exception is caught by the catch block for handling exception ex2 in method1. statement3 is skipped, and statement4 is executed. If the exception type is Exception1, method1 is aborted, the control is returned to the main method, and the exception is caught by the catch block for handling exception ex1 in the main method. statement1 is skipped, and statement2 is executed. If the exception type is not Exception1, Exception2, or Exception3, the exception is not caught and the program terminates. statement1 and statement2 are not executed. Various exception classes can be derived from a common superclass. If a catch block catches exception objects of a superclass, it can catch all the exception objects of the subclasses of that superclass. Page 6

7 م.عبد الغني أبوجبل The order in which exceptions are specified in catch blocks is important. A compilation error will result if a catch block for a superclass type appears before a catch block for a subclass type. For example, the ordering in (a) is erroneous, because RuntimeException is a subclass of Exception. The correct ordering should be as shown in (b). Java forces you to deal with checked exceptions. If a method declares a checked exception (i.e., an exception other than Error or RuntimeException), you must invoke it in a try-catch block or declare to throw the exception in the calling method. For example, suppose that method p1 invokes method p2, and p2 may throw a checked exception (e.g., IOException), you have to write the code as shown in (a) or (b). Getting Information from Exceptions An exception object contains valuable information about the exception. You may use the following instance methods in the java.lang.throwable class to get information regarding the exception, as shown below.the printstacktrace() method prints stack trace information on the console. The getstacktrace() method provides programmatic access to the stack trace information printed by printstacktrace(). Page 7

8 م.عبد الغني أبوجبل Example public class CircleWithException { /** The radius of the circle */ private double radius; /** The number of the objects created */ private static int numberofobjects = 0; /** Construct a circle with radius 1 */ public CircleWithException() { this(1.0); /** Construct a circle with a specified radius */ public CircleWithException(double newradius) { setradius(newradius); numberofobjects++; /** Return radius */ public double getradius() { return radius; /** Set a new radius */ public void setradius(double newradius) throws IllegalArgumentException { if (newradius >= 0 ) radius = newradius; else throw new IllegalArgumentException("Radius cannot be negative"); public static int getnumberofobjects() { return numberofobjects; Test Class: public class TestCircleWithException { /** Main method */ public static void main(string[] args) { try { CircleWithException c1 = new CircleWithException(5); CircleWithException c2 = new CircleWithException(-5); CircleWithException c3 = new CircleWithException(0); catch (IllegalArgumentException ex) { System.out.println(ex); System.out.println("Number of objects created: " + CircleWithException.getNumberOfObjects()); Page 8

9 م.عبد الغني أبوجبل True or False 1) A try block must be followed by a catch and a finally block( ). 2) If you write a method that might cause a compiler-checked exception, you must wrap that risky code in a try-catch block( ). 3) Catch blocks can be polymorphic( ) 4) Only compiler-checked exception can be caught(). 5) If you define a try-catch block, a matching finally block is optional( ). 6) If you define a try block, you can pair it with a matching catch or finally block, or both( ). 7) If you write a method that declares that it can throw a compiler-checked exception, you must also wrap the exception throwing code in a try-catch block( ). 8) The main() method in your program must handle all unhandled exceptions thrown to it( ). 9) A single try block can have many different catch blocks( ). 10) A method can only throw one kind of exception( ). 11) A finally block will run regardless of whether an exception is thrown(). 12) A finally block can exists without a try block( ). 13) A try block can exist by itself, without a catch block or a finally block( ). 14) The order of catch blocks never mattes( ). 15) A method with a try block and a finally block, can optionally declare the exception( ). 16) Runtime exceptions must be handled or declared( ). F,F,T,F,T,T,F,F,T,F,T,F,F,F,F,F Exercise Write a method to test whether a certain Arabic word contains then remove it. consider that they are saved in.txt file.(this exercise is a part from the final project). Page 9

CS115. Chapter 17 Exception Handling. Prof. Joe X. Zhou Department of Computer Science. To know what is exception and what is exception handling

CS115. Chapter 17 Exception Handling. Prof. Joe X. Zhou Department of Computer Science. To know what is exception and what is exception handling CS115 Pi Principles i of fcomputer Science Chapter 17 Exception Handling Prof. Joe X. Zhou Department of Computer Science CS115 ExceptionHandling.1 Objectives in Exception Handling To know what is exception

More information

Chapter 12 Exception Handling

Chapter 12 Exception Handling Chapter 12 Exception Handling 1 Motivations Goal: Robust code. When a program runs into a runtime error, the program terminates abnormally. How can you handle the runtime error so that the program can

More information

Chapter 13 Exception Handling

Chapter 13 Exception Handling Chapter 13 Exception Handling 1 Motivations When a program runs into a runtime error, the program terminates abnormally. How can you handle the runtime error so that the program can continue to run or

More information

CS 112 Programming 2. Lecture 08. Exception Handling & Text I/O (1) Chapter 12 Exception Handling and Text IO

CS 112 Programming 2. Lecture 08. Exception Handling & Text I/O (1) Chapter 12 Exception Handling and Text IO CS 112 Programming 2 Lecture 08 Exception Handling & Text I/O (1) Chapter 12 Exception Handling and Text IO rights reserved. 2 Motivation When a program runs into a runtime error, the program terminates

More information

Chapter 12 Exception Handling and Text IO. Liang, Introduction to Java Programming, Tenth Edition, Global Edition. Pearson Education Limited

Chapter 12 Exception Handling and Text IO. Liang, Introduction to Java Programming, Tenth Edition, Global Edition. Pearson Education Limited Chapter 12 Exception Handling and Text IO Liang, Introduction to Java Programming, Tenth Edition, Global Edition. Pearson Education Limited 2015 1 Motivations When a program runs into a runtime error,

More information

Exception Handling. CSE 114, Computer Science 1 Stony Brook University

Exception Handling. CSE 114, Computer Science 1 Stony Brook University Exception Handling CSE 114, Computer Science 1 Stony Brook University http://www.cs.stonybrook.edu/~cse114 1 Motivation When a program runs into a exceptional runtime error, the program terminates abnormally

More information

BBM 102 Introduction to Programming II Spring Exceptions

BBM 102 Introduction to Programming II Spring Exceptions BBM 102 Introduction to Programming II Spring 2018 Exceptions 1 Today What is an exception? What is exception handling? Keywords of exception handling try catch finally Throwing exceptions throw Custom

More information

Motivations. Chapter 12 Exceptions and File Input/Output

Motivations. Chapter 12 Exceptions and File Input/Output Chapter 12 Exceptions and File Input/Output CS1: Java Programming Colorado State University Motivations When a program runs into a runtime error, the program terminates abnormally. How can you handle the

More information

Assoc. Prof. Marenglen Biba. (C) 2010 Pearson Education, Inc. All rights reserved.

Assoc. Prof. Marenglen Biba. (C) 2010 Pearson Education, Inc. All rights reserved. Assoc. Prof. Marenglen Biba Exception handling Exception an indication of a problem that occurs during a program s execution. The name exception implies that the problem occurs infrequently. With exception

More information

COMP200 EXCEPTIONS. OOP using Java, based on slides by Shayan Javed

COMP200 EXCEPTIONS. OOP using Java, based on slides by Shayan Javed 1 1 COMP200 EXCEPTIONS OOP using Java, based on slides by Shayan Javed Exception Handling 2 3 Errors Syntax Errors Logic Errors Runtime Errors 4 Syntax Errors Arise because language rules weren t followed.

More information

Programming II (CS300)

Programming II (CS300) 1 Programming II (CS300) Chapter 04: Exception Handling MOUNA KACEM mouna@cs.wisc.edu Fall 2018 Creating Classes 2 Introduction Exception Handling Common Exceptions Exceptions with Methods Assertions and

More information

BBM 102 Introduction to Programming II Spring 2017

BBM 102 Introduction to Programming II Spring 2017 BBM 102 Introduction to Programming II Spring 2017 Exceptions Instructors: Ayça Tarhan, Fuat Akal, Gönenç Ercan, Vahid Garousi Today What is an exception? What is exception handling? Keywords of exception

More information

Le L c e t c ur u e e 5 To T p o i p c i s c t o o b e b e co c v o e v r e ed e Exception Handling

Le L c e t c ur u e e 5 To T p o i p c i s c t o o b e b e co c v o e v r e ed e Exception Handling Course Name: Advanced Java Lecture 5 Topics to be covered Exception Handling Exception HandlingHandlingIntroduction An exception is an abnormal condition that arises in a code sequence at run time A Java

More information

Programming II (CS300)

Programming II (CS300) 1 Programming II (CS300) Chapter 04: Exception Handling MOUNA KACEM mouna@cs.wisc.edu Spring 2018 Creating Classes 2 Introduction Exception Handling Common Exceptions Exceptions with Methods Assertions

More information

Object oriented programming. Instructor: Masoud Asghari Web page: Ch: 7

Object oriented programming. Instructor: Masoud Asghari Web page:   Ch: 7 Object oriented programming Instructor: Masoud Asghari Web page: http://www.masses.ir/lectures/oops2017sut Ch: 7 1 In this slide We follow: https://docs.oracle.com/javase/tutorial/index.html Trail: Essential

More information

Lecture 20. Java Exceptional Event Handling. Dr. Martin O Connor CA166

Lecture 20. Java Exceptional Event Handling. Dr. Martin O Connor CA166 Lecture 20 Java Exceptional Event Handling Dr. Martin O Connor CA166 www.computing.dcu.ie/~moconnor Topics What is an Exception? Exception Handler Catch or Specify Requirement Three Kinds of Exceptions

More information

6.Introducing Classes 9. Exceptions

6.Introducing Classes 9. Exceptions 6.Introducing Classes 9. Exceptions Sisoft Technologies Pvt Ltd SRC E7, Shipra Riviera Bazar, Gyan Khand-3, Indirapuram, Ghaziabad Website: www.sisoft.in Email:info@sisoft.in Phone: +91-9999-283-283 Learning

More information

ECE 122. Engineering Problem Solving with Java

ECE 122. Engineering Problem Solving with Java ECE 122 Engineering Problem Solving with Java Lecture 24 Exceptions Overview Problem: Can we detect run-time errors and take corrective action? Try-catch Test for a variety of different program situations

More information

CS159. Nathan Sprague

CS159. Nathan Sprague CS159 Nathan Sprague What s wrong with the following code? 1 /* ************************************************** 2 * Return the mean, or -1 if the array has length 0. 3 ***************************************************

More information

More on Exception Handling

More on Exception Handling Chapter 18 More on Exception Handling Lecture slides for: Java Actually: A Comprehensive Primer in Programming Khalid Azim Mughal, Torill Hamre, Rolf W. Rasmussen Cengage Learning, 2008. ISBN: 978-1-844480-933-2

More information

More on Exception Handling

More on Exception Handling Chapter 18 More on Exception Handling Lecture slides for: Java Actually: A Comprehensive Primer in Programming Khalid Azim Mughal, Torill Hamre, Rolf W. Rasmussen Cengage Learning, 2008. ISBN: 978-1-844480-933-2

More information

Introduction. Exceptions: An OO Way for Handling Errors. Common Runtime Errors. Error Handling. Without Error Handling Example 1

Introduction. Exceptions: An OO Way for Handling Errors. Common Runtime Errors. Error Handling. Without Error Handling Example 1 Exceptions: An OO Way for Handling Errors Introduction Rarely does a program runs successfully at its very first attempt. It is common to make mistakes while developing as well as typing a program. Such

More information

CSCI 261 Computer Science II

CSCI 261 Computer Science II CSCI 261 Computer Science II Department of Mathematics and Computer Science Lecture 2 Exception Handling New Topic: Exceptions in Java You should now be familiar with: Advanced object-oriented design -

More information

Correctness and Robustness

Correctness and Robustness Correctness and Robustness 188230 Advanced Computer Programming Asst. Prof. Dr. Kanda Runapongsa Saikaew (krunapon@kku.ac.th) Department of Computer Engineering Khon Kaen University 1 Agenda Introduction

More information

COE318 Lecture Notes Week 10 (Nov 7, 2011)

COE318 Lecture Notes Week 10 (Nov 7, 2011) COE318 Software Systems Lecture Notes: Week 10 1 of 5 COE318 Lecture Notes Week 10 (Nov 7, 2011) Topics More about exceptions References Head First Java: Chapter 11 (Risky Behavior) The Java Tutorial:

More information

CSC System Development with Java. Exception Handling. Department of Statistics and Computer Science. Budditha Hettige

CSC System Development with Java. Exception Handling. Department of Statistics and Computer Science. Budditha Hettige CSC 308 2.0 System Development with Java Exception Handling Department of Statistics and Computer Science 1 2 Errors Errors can be categorized as several ways; Syntax Errors Logical Errors Runtime Errors

More information

Exceptions. References. Exceptions. Exceptional Conditions. CSE 413, Autumn 2005 Programming Languages

Exceptions. References. Exceptions. Exceptional Conditions. CSE 413, Autumn 2005 Programming Languages References Exceptions "Handling Errors with Exceptions", Java tutorial http://java.sun.com/docs/books/tutorial/essential/exceptions/index.html CSE 413, Autumn 2005 Programming Languages http://www.cs.washington.edu/education/courses/413/05au/

More information

CS 61B Data Structures and Programming Methodology. July 7, 2008 David Sun

CS 61B Data Structures and Programming Methodology. July 7, 2008 David Sun CS 61B Data Structures and Programming Methodology July 7, 2008 David Sun Announcements You ve started (or finished) project 1, right? Package Visibility public declarations represent specifications what

More information

Program Correctness and Efficiency. Chapter 2

Program Correctness and Efficiency. Chapter 2 Program Correctness and Efficiency Chapter 2 Chapter Objectives To understand the differences between the three categories of program errors To understand the effect of an uncaught exception and why you

More information

Comp 249 Programming Methodology Chapter 9 Exception Handling

Comp 249 Programming Methodology Chapter 9 Exception Handling Comp 249 Programming Methodology Chapter 9 Exception Handling Dr. Aiman Hanna Department of Computer Science & Software Engineering Concordia University, Montreal, Canada These slides has been extracted,

More information

Exception Handling. Sometimes when the computer tries to execute a statement something goes wrong:

Exception Handling. Sometimes when the computer tries to execute a statement something goes wrong: Exception Handling Run-time errors The exception concept Throwing exceptions Handling exceptions Declaring exceptions Creating your own exception Ariel Shamir 1 Run-time Errors Sometimes when the computer

More information

Exception Handling. Run-time Errors. Methods Failure. Sometimes when the computer tries to execute a statement something goes wrong:

Exception Handling. Run-time Errors. Methods Failure. Sometimes when the computer tries to execute a statement something goes wrong: Exception Handling Run-time errors The exception concept Throwing exceptions Handling exceptions Declaring exceptions Creating your own exception 22 November 2007 Ariel Shamir 1 Run-time Errors Sometimes

More information

AP COMPUTER SCIENCE JAVA CONCEPTS IV: RESERVED WORDS

AP COMPUTER SCIENCE JAVA CONCEPTS IV: RESERVED WORDS AP COMPUTER SCIENCE JAVA CONCEPTS IV: RESERVED WORDS PAUL L. BAILEY Abstract. This documents amalgamates various descriptions found on the internet, mostly from Oracle or Wikipedia. Very little of this

More information

Day 8. COMP1006/1406 Summer M. Jason Hinek Carleton University

Day 8. COMP1006/1406 Summer M. Jason Hinek Carleton University Day 8 COMP1006/1406 Summer 2016 M. Jason Hinek Carleton University today s agenda assignments Assignment 4 is out and due on Tuesday Bugs and Exception handling 2 Bugs... often use the word bug when there

More information

Exceptions. CSE 142, Summer 2002 Computer Programming 1.

Exceptions. CSE 142, Summer 2002 Computer Programming 1. Exceptions CSE 142, Summer 2002 Computer Programming 1 http://www.cs.washington.edu/education/courses/142/02su/ 12-Aug-2002 cse142-19-exceptions 2002 University of Washington 1 Reading Readings and References»

More information

Exceptions. Readings and References. Exceptions. Exceptional Conditions. Reading. CSE 142, Summer 2002 Computer Programming 1.

Exceptions. Readings and References. Exceptions. Exceptional Conditions. Reading. CSE 142, Summer 2002 Computer Programming 1. Readings and References Exceptions CSE 142, Summer 2002 Computer Programming 1 http://www.cs.washington.edu/education/courses/142/02su/ Reading» Chapter 18, An Introduction to Programming and Object Oriented

More information

14. Exception Handling

14. Exception Handling 14. Exception Handling 14.1 Intro to Exception Handling In a language without exception handling When an exception occurs, control goes to the operating system, where a message is displayed and the program

More information

Data Structures. 02 Exception Handling

Data Structures. 02 Exception Handling David Drohan Data Structures 02 Exception Handling JAVA: An Introduction to Problem Solving & Programming, 6 th Ed. By Walter Savitch ISBN 0132162709 2012 Pearson Education, Inc., Upper Saddle River, NJ.

More information

Checked and Unchecked Exceptions in Java

Checked and Unchecked Exceptions in Java Checked and Unchecked Exceptions in Java Introduction In this article from my free Java 8 course, I will introduce you to Checked and Unchecked Exceptions in Java. Handling exceptions is the process by

More information

Fundamentals of Object Oriented Programming

Fundamentals of Object Oriented Programming INDIAN INSTITUTE OF TECHNOLOGY ROORKEE Fundamentals of Object Oriented Programming CSN- 103 Dr. R. Balasubramanian Associate Professor Department of Computer Science and Engineering Indian Institute of

More information

Sri Vidya College of Engineering & Technology Question Bank

Sri Vidya College of Engineering & Technology Question Bank 1. What is exception? UNIT III EXCEPTION HANDLING AND I/O Part A Question Bank An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program s instructions.

More information

Chapter 9. Exception Handling. Copyright 2016 Pearson Inc. All rights reserved.

Chapter 9. Exception Handling. Copyright 2016 Pearson Inc. All rights reserved. Chapter 9 Exception Handling Copyright 2016 Pearson Inc. All rights reserved. Last modified 2015-10-02 by C Hoang 9-2 Introduction to Exception Handling Sometimes the best outcome can be when nothing unusual

More information

Exceptions - Example. Exceptions - Example

Exceptions - Example. Exceptions - Example - Example //precondition: x >= 0 public void sqrt(double x) double root; if (x < 0.0) //What to do? else //compute the square root of x return root; 1 - Example //precondition: x >= 0 public void sqrt(double

More information

Chapter 8. Exception Handling. CS 180 Sunil Prabhakar Department of Computer Science Purdue University

Chapter 8. Exception Handling. CS 180 Sunil Prabhakar Department of Computer Science Purdue University Chapter 8 Exception Handling CS 180 Sunil Prabhakar Department of Computer Science Purdue University Clarifications Auto cast from char to String does not happen. Cast between int and char happens automatically.

More information

PIC 20A Exceptions. Ernest Ryu UCLA Mathematics. Last edited: November 27, 2017

PIC 20A Exceptions. Ernest Ryu UCLA Mathematics. Last edited: November 27, 2017 PIC 20A Exceptions Ernest Ryu UCLA Mathematics Last edited: November 27, 2017 Introductory example Imagine trying to read from a file. import java.io.*; public class Test { public static void main ( String

More information

Exceptions Handling Errors using Exceptions

Exceptions Handling Errors using Exceptions Java Programming in Java Exceptions Handling Errors using Exceptions Exceptions Exception = Exceptional Event Exceptions are: objects, derived from java.lang.throwable. Throwable Objects: Errors (Java

More information

CS 209 Programming in Java #10 Exception Handling

CS 209 Programming in Java #10 Exception Handling CS 209 Programming in Java #10 Exception Handling Textbook Chapter 15 Spring, 2006 Instructor: J.G. Neal 1 Topics What is an Exception? Exception Handling Fundamentals Errors and Exceptions The try-catch-finally

More information

Exceptions. Produced by. Introduction to the Java Programming Language. Eamonn de Leastar

Exceptions. Produced by. Introduction to the Java Programming Language. Eamonn de Leastar Exceptions Introduction to the Java Programming Language Produced by Eamonn de Leastar edeleastar@wit.ie Department of Computing, Maths & Physics Waterford Institute of Technology http://www.wit.ie http://elearning.wit.ie

More information

Chapter 15. Exception Handling. Chapter Goals. Error Handling. Error Handling. Throwing Exceptions. Throwing Exceptions

Chapter 15. Exception Handling. Chapter Goals. Error Handling. Error Handling. Throwing Exceptions. Throwing Exceptions Chapter 15 Exception Handling Chapter Goals To learn how to throw exceptions To be able to design your own exception classes To understand the difference between checked and unchecked exceptions To learn

More information

Exception Handling Introduction. Error-Prevention Tip 13.1 OBJECTIVES

Exception Handling Introduction. Error-Prevention Tip 13.1 OBJECTIVES 1 2 13 Exception Handling It is common sense to take a method and try it. If it fails, admit it frankly and try another. But above all, try something. Franklin Delano Roosevelt O throw away the worser

More information

Exceptions vs. Errors Exceptions vs. RuntimeExceptions try...catch...finally throw and throws

Exceptions vs. Errors Exceptions vs. RuntimeExceptions try...catch...finally throw and throws Lecture 14 Summary Exceptions vs. Errors Exceptions vs. RuntimeExceptions try...catch...finally throw and throws 1 By the end of this lecture, you will be able to differentiate between errors, exceptions,

More information

Object Oriented Programming Exception Handling

Object Oriented Programming Exception Handling Object Oriented Programming Exception Handling Budditha Hettige Department of Computer Science Programming Errors Types Syntax Errors Logical Errors Runtime Errors Syntax Errors Error in the syntax of

More information

17. Handling Runtime Problems

17. Handling Runtime Problems Handling Runtime Problems 17.1 17. Handling Runtime Problems What are exceptions? Using the try structure Creating your own exceptions Methods that throw exceptions SKILLBUILDERS Handling Runtime Problems

More information

Java Errors and Exceptions. Because Murphy s Law never fails

Java Errors and Exceptions. Because Murphy s Law never fails Java Errors and Exceptions Because Murphy s Law never fails 1 Java is the most distressing thing to hit computing since MS-DOS. Alan Kay 2 Corresponding Book Sections Pearson Custom Computer Science: Chapter

More information

EXCEPTION HANDLING. Summer 2018

EXCEPTION HANDLING. Summer 2018 EXCEPTION HANDLING Summer 2018 EXCEPTIONS An exception is an object that represents an error or exceptional event that has occurred. These events are usually errors that occur because the run-time environment

More information

Exceptions, try - catch - finally, throws keyword. JAVA Standard Edition

Exceptions, try - catch - finally, throws keyword. JAVA Standard Edition Exceptions, try - catch - finally, throws keyword JAVA Standard Edition Java - Exceptions An exception (or exceptional event) is a problem that arises during the execution of a program. When an Exception

More information

COSC 123 Computer Creativity. I/O Streams and Exceptions. Dr. Ramon Lawrence University of British Columbia Okanagan

COSC 123 Computer Creativity. I/O Streams and Exceptions. Dr. Ramon Lawrence University of British Columbia Okanagan COSC 123 Computer Creativity I/O Streams and Exceptions Dr. Ramon Lawrence University of British Columbia Okanagan ramon.lawrence@ubc.ca Objectives Explain the purpose of exceptions. Examine the try-catch-finally

More information

CS 3 Introduction to Software Engineering. 3: Exceptions

CS 3 Introduction to Software Engineering. 3: Exceptions CS 3 Introduction to Software Engineering 3: Exceptions Questions? 2 Objectives Last Time: Procedural Abstraction This Time: Procedural Abstraction II Focus on Exceptions. Starting Next Time: Data Abstraction

More information

Exceptions and Error Handling

Exceptions and Error Handling Exceptions and Error Handling Michael Brockway January 16, 2015 Some causes of failures Incorrect implementation does not meet the specification. Inappropriate object request invalid index. Inconsistent

More information

Administration. Exceptions. Leftovers. Agenda. When Things Go Wrong. Handling Errors. CS 99 Summer 2000 Michael Clarkson Lecture 11

Administration. Exceptions. Leftovers. Agenda. When Things Go Wrong. Handling Errors. CS 99 Summer 2000 Michael Clarkson Lecture 11 Administration Exceptions CS 99 Summer 2000 Michael Clarkson Lecture 11 Lab 10 due tomorrow No lab tomorrow Work on final projects Remaining office hours Rick: today 2-3 Michael: Thursday 10-noon, Monday

More information

Exception Handling. General idea Checked vs. unchecked exceptions Semantics of... Example from text: DataAnalyzer.

Exception Handling. General idea Checked vs. unchecked exceptions Semantics of... Example from text: DataAnalyzer. Exception Handling General idea Checked vs. unchecked exceptions Semantics of throws try-catch Example from text: DataAnalyzer Exceptions [Bono] 1 Announcements Lab this week is based on the textbook example

More information

COMP1008 Exceptions. Runtime Error

COMP1008 Exceptions. Runtime Error Runtime Error COMP1008 Exceptions Unexpected error that terminates a program. Undesirable Not detectable by compiler. Caused by: Errors in the program logic. Unexpected failure of services E.g., file server

More information

CS Programming I: Exceptions

CS Programming I: Exceptions CS 200 - Programming I: Marc Renault Department of Computer Sciences University of Wisconsin Madison Spring 2018 TopHat Sec 3 (AM) Join Code: 427811 TopHat Sec 4 (PM) Join Code: 165455 Command-Line Arguments

More information

What are Exceptions?

What are Exceptions? Exception Handling What are Exceptions? The traditional approach Exception handing in Java Standard exceptions in Java Multiple catch handlers Catching multiple exceptions finally block Checked vs unchecked

More information

Exceptions. Produced by. Algorithms. Eamonn de Leastar Department of Computing, Maths & Physics Waterford Institute of Technology

Exceptions. Produced by. Algorithms. Eamonn de Leastar Department of Computing, Maths & Physics Waterford Institute of Technology Exceptions Algorithms Produced by Eamonn de Leastar edeleastar@wit.ie Department of Computing, Maths & Physics Waterford Institute of Technology http://www.wit.ie http://elearning.wit.ie Exceptions ± Definition

More information

Exception Handling Generics. Amit Gupta

Exception Handling Generics. Amit Gupta Exception Handling Generics Amit Gupta Announcements Project 2 deadline 18 th Feb 9 pm. TA Consulting hours Mon Thurs B146 6 9 pm Exam 1 : Feb 15 4:30 5:20 pm Project 1 grading Exception Handling Computer

More information

Full file at Chapter 2 - Inheritance and Exception Handling

Full file at   Chapter 2 - Inheritance and Exception Handling Chapter 2 - Inheritance and Exception Handling TRUE/FALSE 1. The superclass inherits all its properties from the subclass. ANS: F PTS: 1 REF: 76 2. Private members of a superclass can be accessed by a

More information

CSC207H: Software Design. Exceptions. CSC207 Winter 2018

CSC207H: Software Design. Exceptions. CSC207 Winter 2018 Exceptions CSC207 Winter 2018 1 What are exceptions? Exceptions represent exceptional conditions: unusual, strange, disturbing. These conditions deserve exceptional treatment: not the usual go-tothe-next-step,

More information

Exceptions. CSC207 Winter 2017

Exceptions. CSC207 Winter 2017 Exceptions CSC207 Winter 2017 What are exceptions? In Java, an exception is an object. Exceptions represent exceptional conditions: unusual, strange, disturbing. These conditions deserve exceptional treatment:

More information

Exception Handling. Chapter 9

Exception Handling. Chapter 9 Exception Handling Chapter 9 Objectives Describe the notion of exception handling React correctly when certain exceptions occur Use Java's exception-handling facilities effectively in classes and programs

More information

CS 11 java track: lecture 3

CS 11 java track: lecture 3 CS 11 java track: lecture 3 This week: documentation (javadoc) exception handling more on object-oriented programming (OOP) inheritance and polymorphism abstract classes and interfaces graphical user interfaces

More information

CS159. Nathan Sprague

CS159. Nathan Sprague CS159 Nathan Sprague What s wrong with the following code? 1 /* ************************************************** 2 * Return the maximum, or Integer. MIN_VALUE 3 * if the array has length 0. 4 ***************************************************

More information

Exceptions and Libraries

Exceptions and Libraries Exceptions and Libraries RS 9.3, 6.4 Some slides created by Marty Stepp http://www.cs.washington.edu/143/ Edited by Sarah Heckman 1 Exceptions exception: An object representing an error or unusual condition.

More information

Lecture 14 Summary 3/9/2009. By the end of this lecture, you will be able to differentiate between errors, exceptions, and runtime exceptions.

Lecture 14 Summary 3/9/2009. By the end of this lecture, you will be able to differentiate between errors, exceptions, and runtime exceptions. Lecture 14 Summary Exceptions vs. Errors Exceptions vs. RuntimeExceptions...catch...finally throw and throws By the end of this lecture, you will be able to differentiate between errors, exceptions, and

More information

Topic 6: Exceptions. Exceptions are a Java mechanism for dealing with errors & unusual situations

Topic 6: Exceptions. Exceptions are a Java mechanism for dealing with errors & unusual situations Topic 6: Exceptions Exceptions are a Java mechanism for dealing with errors & unusual situations Goals: learn how to... think about different responses to errors write code that catches exceptions write

More information

CSCI Object Oriented Design: Java Review Errors George Blankenship. Java Review - Errors George Blankenship 1

CSCI Object Oriented Design: Java Review Errors George Blankenship. Java Review - Errors George Blankenship 1 CSCI 6234 Object Oriented Design: Java Review Errors George Blankenship Java Review - Errors George Blankenship 1 Errors Exceptions Debugging Java Review Topics Java Review - Errors George Blankenship

More information

Why Exceptions? (1.1) Exceptions. Why Exceptions? (1.2) Caller vs. Callee. EECS2030 B: Advanced Object Oriented Programming Fall 2018

Why Exceptions? (1.1) Exceptions. Why Exceptions? (1.2) Caller vs. Callee. EECS2030 B: Advanced Object Oriented Programming Fall 2018 Why Exceptions? (1.1) Exceptions EECS2030 B: Advanced Object Oriented Programming Fall 2018 CHEN-WEI WANG 1 class Circle { 2 double radius; 3 Circle() { /* radius defaults to 0 */ 4 void setradius(double

More information

CSCI Object-Oriented Design. Java Review Topics. Program Errors. George Blankenship 1. Java Review Errors George Blankenship

CSCI Object-Oriented Design. Java Review Topics. Program Errors. George Blankenship 1. Java Review Errors George Blankenship CSCI 6234 Object Oriented Design: Java Review Errors George Blankenship George Blankenship 1 Errors Exceptions Debugging Java Review Topics George Blankenship 2 Program Errors Types of errors Compile-time

More information

Exceptions. EECS2030 B: Advanced Object Oriented Programming Fall 2018 CHEN-WEI WANG

Exceptions. EECS2030 B: Advanced Object Oriented Programming Fall 2018 CHEN-WEI WANG Exceptions EECS2030 B: Advanced Object Oriented Programming Fall 2018 CHEN-WEI WANG Caller vs. Callee Within the body implementation of a method, we may call other methods. 1 class C1 { 2 void m1() { 3

More information

Exception Handling: Control. Exception handling is the control of error conditions or other unusual events during the execution of a program.

Exception Handling: Control. Exception handling is the control of error conditions or other unusual events during the execution of a program. Exception Handling: Control Exception handling is the control of error conditions or other unusual events during the execution of a program. 1 In a language without exception handling: When an exception

More information

Exceptions, Case Study-Exception handling in C++.

Exceptions, Case Study-Exception handling in C++. PART III: Structuring of Computations- Structuring the computation, Expressions and statements, Conditional execution and iteration, Routines, Style issues: side effects and aliasing, Exceptions, Case

More information

Chapter 14. Exception Handling and Event Handling ISBN

Chapter 14. Exception Handling and Event Handling ISBN Chapter 14 Exception Handling and Event Handling ISBN 0-321-49362-1 Chapter 14 Topics Introduction to Exception Handling Exception Handling in Ada Exception Handling in C++ Exception Handling in Java Introduction

More information

National University. Faculty of Computer Since and Technology Object Oriented Programming

National University. Faculty of Computer Since and Technology Object Oriented Programming National University Faculty of Computer Since and Technology Object Oriented Programming Lec (8) Exceptions in Java Exceptions in Java What is an exception? An exception is an error condition that changes

More information

Introduction to Programming Using Java (98-388)

Introduction to Programming Using Java (98-388) Introduction to Programming Using Java (98-388) Understand Java fundamentals Describe the use of main in a Java application Signature of main, why it is static; how to consume an instance of your own class;

More information

CS112 Lecture: Exceptions. Objectives: 1. Introduce the concepts of program robustness and reliability 2. Introduce exceptions

CS112 Lecture: Exceptions. Objectives: 1. Introduce the concepts of program robustness and reliability 2. Introduce exceptions CS112 Lecture: Exceptions Objectives: 1. Introduce the concepts of program robustness and reliability 2. Introduce exceptions Materials: 1. Online Java documentation to project 2. ExceptionDemo.java to

More information

EXCEPTION-HANDLING INTRIVIEW QUESTIONS

EXCEPTION-HANDLING INTRIVIEW QUESTIONS EXCEPTION-HANDLING INTRIVIEW QUESTIONS Q1.What is an Exception? Ans.An unwanted, unexpected event that disturbs normal flow of the program is called Exception.Example: FileNotFondException. Q2.What is

More information

About This Lecture. Outline. Handling Unusual Situations. Reacting to errors. Exceptions

About This Lecture. Outline. Handling Unusual Situations. Reacting to errors. Exceptions Exceptions Revised 24-Jan-05 CMPUT 115 - Lecture 4 Department of Computing Science University of Alberta About This Lecture In this lecture we will learn how to use Java Exceptions to handle unusual program

More information

Lecture 19 Programming Exceptions CSE11 Fall 2013

Lecture 19 Programming Exceptions CSE11 Fall 2013 Lecture 19 Programming Exceptions CSE11 Fall 2013 When Things go Wrong We've seen a number of run time errors Array Index out of Bounds e.g., Exception in thread "main" java.lang.arrayindexoutofboundsexception:

More information

ITI Introduction to Computing II

ITI Introduction to Computing II ITI 1121. Introduction to Computing II Marcel Turcotte School of Electrical Engineering and Computer Science Version of February 23, 2013 Abstract Handling errors Declaring, creating and handling exceptions

More information

Abstract Classes, Exceptions

Abstract Classes, Exceptions CISC 370: Inheritance, Abstract Classes, Exceptions June 15, 1 2006 1 Review Quizzes Grades on CPM Conventions Class names are capitalized Object names/variables are lower case String.doStuff dostuff();

More information

CS1020 Data Structures and Algorithms I Lecture Note #8. Exceptions Handling exceptional events

CS1020 Data Structures and Algorithms I Lecture Note #8. Exceptions Handling exceptional events CS1020 Data Structures and Algorithms I Lecture Note #8 Exceptions Handling exceptional events Objectives Understand how to use the mechanism of exceptions to handle errors or exceptional events that occur

More information

Contents. I Introductory Examples. Topic 06 -Exception Handling

Contents. I Introductory Examples. Topic 06 -Exception Handling Contents Topic 06 - Handling I. Introductory Examples (Example 1-5) II. Handling Basic Idea III. Hierarchy IV. The Try-throw-catch Mechanism V. Define our own classes (Example 6) VI. Pitfall: Catch the

More information

Java Loose Ends. 11 December 2017 OSU CSE 1

Java Loose Ends. 11 December 2017 OSU CSE 1 Java Loose Ends 11 December 2017 OSU CSE 1 What Else? A few Java issues introduced earlier deserve a more in-depth treatment: Try-Catch and Exceptions Members (static vs. instance) Nested interfaces and

More information

Exceptions. Examples of code which shows the syntax and all that

Exceptions. Examples of code which shows the syntax and all that Exceptions Examples of code which shows the syntax and all that When a method might cause a checked exception So the main difference between checked and unchecked exceptions was that the compiler forces

More information

ITI Introduction to Computing II

ITI Introduction to Computing II ITI 1121. Introduction to Computing II Marcel Turcotte School of Electrical Engineering and Computer Science Version of February 23, 2013 Abstract Handling errors Declaring, creating and handling exceptions

More information

Exceptions Questions https://www.journaldev.com/2167/java-exception-interview-questionsand-answers https://www.baeldung.com/java-exceptions-interview-questions https://javaconceptoftheday.com/java-exception-handling-interviewquestions-and-answers/

More information

EXCEPTIONS. Fundamentals of Computer Science I

EXCEPTIONS. Fundamentals of Computer Science I EXCEPTIONS Exception in thread "main" java.lang.numberformatexception: For input string: "3.5" at java.lang.numberformatexception.forinputstring(numberformatexception.java:48) at java.lang.integer.parseint(integer.java:458)

More information

Exception handling & logging Best Practices. Angelin

Exception handling & logging Best Practices. Angelin Exception handling & logging Best Practices Angelin AGENDA Logging using Log4j Logging Best Practices Exception Handling Best Practices CodePro Errors and Fixes Logging using Log4j Logging using Log4j

More information

Introduction to Java. Handout-3a. cs402 - Spring

Introduction to Java. Handout-3a. cs402 - Spring Introduction to Java Handout-3a cs402 - Spring 2003 1 Exceptions The purpose of exceptions How to cause an exception (implicitely or explicitly) How to handle ( catch ) an exception within the method where

More information

CS Programming I: Exceptions

CS Programming I: Exceptions CS 200 - Programming I: Exceptions Marc Renault Department of Computer Sciences University of Wisconsin Madison Fall 2017 TopHat Sec 3 (PM) Join Code: 719946 TopHat Sec 4 (AM) Join Code: 891624 Command-Line

More information