Java Expection Handling

11 Key excerpts on "Java Expection Handling"

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  eBook - PDF

  An Object-Oriented Approach to Programming Logic and Design

  • Joyce Farrell(Author)
  • 2012(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  C H A P T E R 10 Exception Handling In this chapter, you will learn about: Exceptions The limitations of traditional error handling Trying code and catching exceptions Throwing and catching multiple exceptions Using the finally block The advantages of exception handling Tracing exceptions through the call stack Creating your own exceptions Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Learning About Exceptions An exception is an unexpected or error condition that occurs while a program is running. The programs you write can generate many types of potential exceptions, including the following: l The program issues a command to read a file from a disk, but the file does not exist there. l The program attempts to write data to a disk, but the disk is full. l The program asks for user input, but the user enters invalid data. l The program attempts to divide a value by 0. l The program tries to access an array using a subscript that is too large. l The program calculates a value that exceeds the limit of its variable type. These errors are called exceptions because they are not usual occurrences; they are “ exceptional. ” The object-oriented techniques to manage such errors comprise the group of techniques known as exception handling . Sometimes, computer programs generate errors from which the programmer cannot write code to recover. For example, a power failure might interrupt production of your paycheck. Exception handling does not deal with these kinds of errors; its concern is predictable errors.

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  Java Programming

  • Joyce Farrell(Author)
  • 2018(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  C H A P T E R 12 Exception Handling Upon completion of this chapter, you will be able to: Describe exceptions Try code and catch exceptions Throw and catch multiple exceptions Use the finally block Appreciate the advantages of exception handling Specify the exceptions that a method can throw Trace exceptions through the call stack Create your own Exception classes Use an assertion Display a virtual keyboard Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 571 Learning About Exceptions Learning About Exceptions An exception is an unexpected or error condition. The programs you write can generate many types of potential exceptions. As examples: • A program might issue a command to read a file from a disk, but the file does not exist there. • A program might attempt to write data to a disk, but the disk is full or unformatted. • A program might ask for user input, but the user enters an invalid data type. • A program might attempt to divide a value by 0. • A program might try to access an array with a subscript that is too large or too small. These errors are called exceptions because, presumably, they are not usual occurrences; they are “exceptional.” Exception handling is the name for the object-oriented techniques that manage or resolve such errors. Unplanned exceptions that occur during a program’s execution are also called runtime exceptions, in contrast with syntax errors that are discovered during program compilation.

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  eBook - ePub

  Creating Components

  Object Oriented, Concurrent, and Distributed Computing in Java

  • Charles W. Kann(Author)
  • 2017(Publication Date)
  • Auerbach Publications

    (Publisher)

  This forces the programmer to insert similar code around every file opened to check for a problem. This is referred to as micromanaging an error and ideally should be avoided. Because of the drawbacks of handling errors where they occur and return codes, Java implements error handling using a “try-catch” mechanism, similar to the “try-catch” mechanisms in C++ or Exception blocks in Ada. However, unlike C++ (which, unfortunately, was built on top of C and has a mixed mode for exception handling of try-catch and return values), the exception handling in Java is consistently built around using these try-catch blocks. And, unlike Ada and C++, Java implements checked exceptions that can validate that a program does in fact handle errors that are likely to occur. The rest of this chapter explains how exception handling is implemented in Java. 6.4 Java Exception Handling This section covers the basic mechanism for handling Java exceptions. Generation and handling of exceptions is shown through the use of try-catch blocks. First, simple try-catch blocks and the actions that can be taken in a catch block are shown, then more complicated behaviors of try-catch blocks, such as exception propagation, finally blocks, and re-throwing of exceptions, are discussed. The basic structure of exceptions handling demonstrated in this section is used in subsequent discussion regarding the uses of exceptions in designing components. 6.4.1 Try-Catch Blocks The basic mechanism in Java for handling problems that occur at run time is to try to run a section of code. If it completes normally, then the program proceeds to the next statement after all associated catch blocks. However, if a problem is encountered, the program immediately throws the error. The program then looks at each enclosing try block to see if any mechanism to catch the error has been defined

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  Microsoft® Visual C# 2015

  An Introduction to Object-Oriented Programming

  • Joyce Farrell, , , (Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  You might grumble, “If the program knows what is wrong, why doesn’t it just fix the problem?” In this chapter, you will learn how to handle these unexpected error conditions so your programs can be more user-friendly than those that simply shut down in the face of errors. Understanding Exceptions An exception is any error condition or unexpected behavior in an executing program. Exceptions are caused by errors in program logic or insufficient system resources. The programs you write can generate many types of potential exceptions, including when: • Your program asks for user input, but the user enters invalid data. • The program attempts to divide an integer by zero. • You attempt to access an array with a subscript that is too large or too small. • You calculate a value that is too large for the answer’s variable type. These errors are called exceptions because presumably they are not usual occurrences; they are “exceptional.” The object-oriented techniques used to manage such errors make up the group of methods known as exception handling . If you do not handle an exception, the running program terminates abruptly. Managing exceptions involves an oxymoron; you must expect the unexpected. Errors you discover when compiling a program are not exceptions; they are compiler errors. Only execution-time (also called runtime ) errors are called exceptions. In C#, all exceptions are objects that are instances of the Exception class or one of its derived classes. An exception condition generates an object that encapsulates information about the error. Like all other classes in the C# programming language, the Exception class is a descendent of the Object class. The Exception class has several descendent classes of its own, many with unusual names such as CodeDomSerializerException , SUDSParserException , and SoapException .

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  C++ Programming

  Program Design Including Data Structures

  • D. Malik(Author)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Exception Handling IN THIS CHAPTER, YOU WILL: 1. Learn what an exception is 2. Learn how to handle exceptions within a program 3. Learn how a try / catch block is used to handle exceptions 4. Learn how to throw an exception 5. Become familiar with C 11 exception classes and how to use them in a program 6. Learn how to create your own exception classes 7. Discover how to throw and rethrow an exception 8. Explore exception-handling techniques 9. Explore stack unwinding 14 CHAPTER © HunThomas/Shutterstock.com Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 1008 | Chapter 14: Exception Handling An exception is an occurrence of an undesirable situation that can be detected during program execution. For example, division by zero is an exception. Similarly, trying to open an input file that does not exist is an exception, as is an array index that goes out of bounds. Until now, we have dealt with certain exceptions by using either an if statement or the assert function. For instance, in Examples 5-3 and 5-4, before dividing sum by counter or count , we checked whether counter or count was nonzero. Similarly, in the Programming Example newString (Chapter 13), we used the assert function to determine whether the array index is within bounds. On the other hand, there were places where we simply ignored the exception. For instance, while determining a substring in a string (Chapter 7), we never checked whether the starting position of the substring was within range. Also, we did not han-dle the array index out-of-bounds exception. However, in all of these cases, if excep-tions occurred during program execution, either we included code to terminate the program or the program terminated with an appropriate error message. For instance, if we opened an input file in the function main and the input file did not exist, we terminated the function main , so the program was terminated.

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  eBook - ePub

  Software Mistakes and Tradeoffs

  How to make good programming decisions

  • Tomasz Lelek, Jon Skeet(Authors)
  • 2022(Publication Date)
  • Manning

    (Publisher)

  Error , it means that a critical problem has occurred, and most often, you should not try to catch or handle it. It can be, for example, a virtual machine error that signals a critical problem with the environment.

  In this chapter, we won’t focus on Java error handling because we don’t have much control over it. We will, however, consider different strategies for exception handling. Also note that in the rest of the chapter, I will use the words error and exception interchangeably for the same concept.

  On the left side of figure 3.1, you can see the exceptions. We should use those to signal problems within our code. Moreover, we should also handle them if there is a way to recover gracefully. In fact, if a method declares a checked exception, then the compiler requires a caller to handle such an exception (it can be caught or rethrown). This means that your code will not compile until you handle it. For example, if you load some files and get an IOException , it may be reasonable to recover and try to load it from a different place on your filesystem. Later, we will use those exceptions to design an error-handling API explicitly.

  On the other hand, we are not required to handle unchecked exceptions. But if your code does not handle these, they are propagated to the main application thread and will stop your application. They often signal some usage error that cannot be recovered, and it is better to fail fast than to try to recover from such an error. For example, if you pass a negative number as an argument to a method that expects a positive number, you may decide to throw an unchecked exception because there is no point in trying to recover. The callers may also prefer to use unchecked exceptions to simplify using them from a functional interface (lambda) API, for example. This is the implicit part of the error handling code.

  The concept of checked or unchecked exceptions is also present in other languages, but most of those pick one strategy or the other. For example, in the Scala and C# programming languages, every exception is treated as unchecked; therefore, you don’t need to catch them. However, you need to be careful not to propagate exceptions up to the main thread. Otherwise, your program will stop.

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  eBook - PDF

  Microsoft Visual C#: An Introduction to Object-Oriented Programming

  • Joyce Farrell(Author)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  • Exceptions do not have to be caught by the methods that generate them. Instead, a program that calls a method that throws an exception can catch and handle it. Often, this approach produces the best software design. • If a method throws an exception and does not catch it, then the Exception object is thrown to the calling method. When you catch an Exception object, you can display the value of the StackTrace property, which provides a list of methods in the call stack, allowing you to determine the location where the error occurred. • To create your own Exception classes from which you create throwable objects, you can extend the ApplicationException class or the Exception class. The current advice is to extend Exception . • When you write a method that catches an exception, your method does not have to handle it. Instead, you might choose to rethrow the exception to the method that called your method and let that method handle it. Key Terms An exception is any error condition or unexpected behavior in an executing program. Exception handling is the set of object-oriented techniques used to manage unexpected errors in an executing program. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Review Questions 527 Mission critical describes any process that is crucial to an organization. Fault-tolerant applications are designed so that they continue to operate, possibly at a reduced level, when some part of the system fails. Robustness represents the degree to which a system is resilient to stress, maintaining correct functioning even in the presence of errors.

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  eBook - ePub

  100+ Solutions in Java

  A Hands-On Introduction to Programming in Java: A Hands-On Introduction to Programming in Java (English Edition)

  • Dhruti Shah, DHRUTI SHAH(Authors)
  • 2020(Publication Date)
  • BPB Publications

    (Publisher)

  HAPTER 6

  Exceptions and Regular Expressions

  I n this chapter, you will learn how to handle exceptions in Java by using the different built-in Exception classes. You will also learn how to create custom exceptions and work with assertions. Further, you will learn how to use the important classes of java.lang and java.util.regex packages.

  Structure

  • Exceptions in Java
  • Exception class in Java
  • Exception handling in Java
  • Using the try-with-resources statement
  • Custom exceptions
  • Wrapper exceptions
  • Assertions in Java
  • Classes of the java.lang package
  • Regular expressions
  • Character classes

  Objectives

  • Understand exception handling in Java
  • Learn about built-in exception classes
  • Create custom exceptions
  • Work with assertions in Java
  • Learn about the java.lang package
  • Work with regular expressions

  6.1 Exceptions in Java

  Any abnormal or unexpected event occurring in a program that disrupts its normal execution is termed as an exception. There can be different types of exceptions and reasons for exceptions such as an attempt to open a file that does not exist, invalid data specified to a method, network connection error, or out of memory error. The information about the error is stored in the exception object that is passed to the runtime.

  An exception occurring in a method can be thrown by using the exception object of the type of exception that occurred. The runtime looks for a handler code that can handle the exception in the same method. If it does not find a handler, it searches the entire method call stack to find an appropriate exception handler. If the runtime does not find a handler in the entire call stack, it will eventually terminate the program.

  The sequence in which methods are invoked inside another method(s) is called a call stack. A stack trace shows the sequence in which methods were invoked that led to the exception.

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  No longer available |Learn more

  Programming Fundamentals Using JAVA

  A Game Application Approach

  • William McAllister, S. Jane Fritz(Authors)
  • 2021(Publication Date)
  • Mercury Learning and Information

    (Publisher)

  HAPTER 10

  EXCEPTIONS : A SECOND LOOK

  10.1 An Overview

  10.2 Java’s Exception Classes and Exception Objects

  10.3 Processing Thrown Exceptions

  10.4 The Throw Statement and Error Messages

  10.5 Defining Exception Classes

  10.6 Chapter Summary

  In this chapter

  In this chapter, we will discuss the features Java provides within its implementation of the concept of exceptions. This will expand our knowledge of the try-catch construct, the API exception classes, and the differences between checked and unchecked exceptions, which were discussed in the context of performing disk I/O. In addition, we will learn how to write methods that throw exceptions when they detect errors, as the methods in the API classes do, and how to create our own exception classes that make our programs more readable. We will also discuss ways of using exceptions to facilitate the implementation of methods that do not normally detect errors and the role of the finally

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  eBook - ePub

  OCP Oracle Certified Professional Java SE 11 Programmer I Study Guide

  Exam 1Z0-815

  • Jeanne Boyarsky, Scott Selikoff(Authors)
  • 2019(Publication Date)
  • Sybex

    (Publisher)

  Chapter 10 Exceptions

  OCP exam objectives covered in this chapter:

  •   Handling Exceptions
    • Describe the advantages of Exception handling and differentiate among checked, unchecked exceptions, and Errors
    • Create try-catch blocks and determine how exceptions alter program flow
    • Create and invoke a method that throws an exception

   Many things can go wrong in a program. Java uses exceptions to deal with some of these scenarios. This chapter focuses on how exceptions are created, how to handle them, and how to distinguish between various types of exceptions and errors.

  Understanding Exceptions

  A program can fail for just about any reason. Here are just a few possibilities:

  • The code tries to connect to a website, but the Internet connection is down.
  • You made a coding mistake and tried to access an invalid index in an array.
  • One method calls another with a value that the method doesn’t support.

  As you can see, some of these are coding mistakes. Others are completely beyond your control. Your program can’t help it if the Internet connection goes down. What it can do is deal with the situation.

  First, we’ll look at the role of exceptions. Then we’ll cover the various types of exceptions, followed by an explanation of how to throw an exception in Java.

  The Role of Exceptions

  An

  exception

  is Java’s way of saying, “I give up. I don’t know what to do right now. You deal with it.” When you write a method, you can either deal with the exception or make it the calling code’s problem.

  As an example, think of Java as a child who visits the zoo. The

  happy path

  is when nothing goes wrong. The child continues to look at the animals until the program nicely ends. Nothing went wrong, and there were no exceptions to deal with.

  This child’s younger sister doesn’t experience the happy path. In all the excitement she trips and falls. Luckily, it isn’t a bad fall. The little girl gets up and proceeds to look at more animals. She has handled the issue all by herself. Unfortunately, she falls again later in the day and starts crying. This time, she has declared she needs help by crying. The story ends well. Her daddy rubs her knee and gives her a hug. Then they go back to seeing more animals and enjoy the rest of the day.

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  eBook - PDF

  Programming with C++

  • Kyla McMullen, Elizabeth Matthews, June Jamrich Parsons, , Kyla McMullen, Kyla McMullen, Elizabeth Matthews, June Jamrich Parsons(Authors)
  • 2021(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  It is the respon- sibility of a programmer to know, or know how to look up, the types of exceptions available in the language they use. Most programming languages also allow you to create your own exception types for special situations. For example, with Iceabella, you might make a specific no_cream_error exception. Q Should you use a default exception to handle everything? A No. Handling everything the same way would be similar to displaying only very generic computer messages. “Something went wrong” isn’t as helpful as “You couldn’t print your document because the printer needs ink.” For example, in the ice cream video game, Iceabella stating that she can’t make ice cream doesn’t help you understand how to fix the problem. If she tells you she needs cream first, you know you need to give her cream. Specific exception types narrow the possible ways to solve the problem and let the program return to its normal flow. Many specific exceptions, which differ by programming language, are available to programmers. Figure 11-3 shows some of the most common exception types you might need. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Module 11 exceptions 189 11.2 DEALING WITH EXCEPTIONS Handling Others’ Exceptions (11.2.1, 11.2.2) When code causes an exception, programmers say the code “throws” an exception. Programmers make their code throw exceptions when certain conditions are true. Handling the exception is more important than investi- gating why it was thrown in the first place.

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