Java Try Catch

12 Key excerpts on "Java Try Catch"

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  eBook - PDF

  Software Essentials

  Design and Construction

  • Adair Dingle(Author)
  • 2014(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  Three statements typically support exception handling in modern pro-gramming languages: try, throw, and catch. In many languages, these three specific words are, in fact, reserved words. A try block is the speci-fication of a code block that is to be guarded or enclosed by exception handling. Essentially then, the try block is a signal to the compiler that, when the software runs, if exceptions are thrown in the guarded code then execution should jump to the appropriate error-handling code. A catch block is an exception handler , the specification of code to execute when an exception arises. A named catch block is associated with one or more exceptions that are identified. An unnamed catch block processes all (remaining) exceptions. Throw is an intentional, direct raising of an exception. Software Correctness ◾ 271 Exception handling is an oft neglected component of software design. Code should be analyzed to determine its vulnerability to error. The expected frequency and severity of error should be estimated alongside the cost of error response. What type of errors merit the overhead of exception handling? This question cannot be answered independent of an application, and its prioritization of design goals. When disruptive errors are anticipated and exception handling is to be used, code is placed in a try block. The try block is followed by one or more “catch” blocks and an optional “finally” block. Example 9.1 illustrates some common exceptions, using pseudo-code that is similar to exception handling code in modern languages. Figure 9.1 shows the corresponding possible execution paths through this code. Example 9.1: Pseudo-Code for Exception Handling try // exact syntax is LANGUAGE DEPENDENT { x = y/z; // A1: division by zero possible ptr->data = 100; // A2: null pointer possible if (myExceptionCond) // A3: throw specified exception throw new MyException(“Error”, and_other_data); ...

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  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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  An Object-Oriented Approach to Programming Logic and Design

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

    (Publisher)

  In object-oriented methods, you detect errors but allow the client to handle them appropriately. In object-oriented terminology, a client tries some code that might cause an error. The code that detects an error condition throws an exception , and you can create a block of code that catches the exception and takes appropriate action. Trying Code and Catching Exceptions When you create a segment of code in which something might go wrong, you place the code in a try block , which is a block of code you attempt to execute while acknowledging that an exception might occur. A try block consists of the keyword try followed by any number of statements, some of which might cause exceptions. (Some of the statements might be method calls, and the methods might throw exceptions.) If a statement in the block causes an exception, the remaining statements in the try block do not execute and the try block is abandoned. For pseudocode purposes, you can end a try block with a sentinel such as endtry . You almost always code at least one catch block immediately following a try block. A catch block is a segment of code written to handle an exception that might be thrown by the try block that precedes it. A throw statement sends an exception object out of a method so it can be handled elsewhere. Each catch block can “ catch ” one type of exception — that is, one object of the type Exception or one of its child classes. You create a catch block using the following elements: l The keyword catch followed by parentheses that contain an Exception type and an identifier l Statements that take the action to handle the error condition l An endcatch statement that indicates the end of the catch block in the pseudocode In some object-oriented programming languages, notably C++, you can throw a number or string as well as an exception. Figure 10-4 shows the general format of a method that includes a shaded try … catch pair.

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  Programming Fundamentals Using JAVA

  A Game Application Approach

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

    (Publisher)

  They are not caused by programming errors, an I/O error, or something that can be dealt with within an application. When they do occur, they are best processed by the Java Runtime environment, the catcher of all uncaught exceptions. Runtime errors that generate checked exceptions are considered to be situations that can be dealt with by a method within an application and are serious enough that the translator requires that they either are dealt with or that the method indicates that it is intentionally ignoring the error via a throws clause. Errors that cause instances of the class RunTimeError or its descendants to be thrown are considered errors that will be eliminated during the testing phase of the application’s development, and therefore, the translator does not require that the application process these errors or indicate that they are intentionally being ignored via a throws clause. In situations where the programmer feels that erroneous input or other non-programming error-related events could cause these unchecked exception objects to be thrown, a try-catch construct should be included in the portions of the application where these events could occur. 10.3 PROCESSING THROWN EXCEPTIONS Exceptions are processed using a try-catch construct. The construct consists of a try clause that is immediately followed by a catch clause. The statements associated with each of these clauses are always enclosed in a set of brackets, even if there is only one statement associated with them. For this reason, they are commonly referred to as try and catch blocks. The try block is used to detect thrown exceptions, and the catch block is used to process the errors that produced the exceptions. As illustrated in Figure 10.2, one try block can be followed by multiple catch blocks, and the catch blocks must immediately follow the try block. Coding statements in between any of the blocks is a syntax error

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  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)

  You can write code to detect the exception and handle it as you decide is best. The code to detect an exception uses a similar logical control structure to an if-else block. The logical flow of the program changes depending on whether an exception occurs. Generally, to work with exceptions, programs try to do something and catch any exceptions that were thrown in the code. Try and Catch Blocks (11.2.3, 11.2.4, 11.2.5, 11.2.6) You can use a program flow control for trying and catching exceptions. The program flow control is called a try-catch block. (Some languages, including Python, refer to this program flow control as a try-except block). A try-catch block has two parts: the try block and the catch block. The try code attempts to proceed as if condi- tions are normal and nothing disrupts the program flow. If an exception is thrown in the try block, the program flow moves to the catch block. Figure 11-4 shows a diagram of the flow for a try-catch block. Figure 11-4 Try-catch block logic flow main program program continues try block Exception is thrown at any point catch block 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.

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  Developing Java Software

  • Russel Winder, Graham Roberts(Authors)
  • 2014(Publication Date)
  • Wiley

    (Publisher)

  A sequence of statements that may result in an exception being thrown when executed is wrapped in a try block, which is just a compound statement preceded by the keyword try . Associated with the try block are one or more catch blocks, which is a compound statement preceded by the keyword catch followed by the declaration of a variable of an exception type (subclass of Throwable) in parentheses. A catch block is a block with an exception type parameter specifying which type of exception object the block will catch. For example: try { anObject.f ( ) ; anotherObject.g ( ) ; } catch ( SomeException se ) { // do something to recover } catch ( SomeOtherException soe ) { 8.5 Catching Exceptions ! throw and throws are two distinct keywords. ! The catch block variables are all in the same scope and so must all have distinct names. ref See Chapter 23, page 787, for a detailed description of exceptions. 276 Chapter 8: Exceptions // do something to recover } The methods anObject.f and anotherObject.g may throw exceptions and so they are within a try block. The possible types exceptions that can be thrown are SomeException or SomeOtherException, so there are catch block associated with the try block for each of those types. The try block will be executed as part of the usual order of execution. If no exception is thrown then when the sequence is complete, control transfers to the statement following the whole try–catch block, i.e. all the catch blocks are ignored. If an exception is thrown the execution of the statement sequence in the try block stops immediately and an attempt is made to find an appropriate catch block to catch the exception. A search is made through all the catch blocks associated with the try block in the order they appear in the code to see if one of the catch blocks’ exception variables is of the same type or a supertype of the exception thrown. If a matching catch block is found then the statement sequence in that block is executed.

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  Microsoft® Visual C# 2015

  An Introduction to Object-Oriented Programming

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

    (Publisher)

  If an application might throw several types of exceptions, you can try some code, catch the possible exception, try some more code, catch the possible exception, and so on. Usually, however, the superior approach is to try all the statements that might throw exceptions, then include all the needed catch blocks and an optional finally block. This is the approach shown in Figure 11-21, and it usually results in logic that is easier to follow. You often can avoid using a finally block, but you would need repetitious code. For example, instead of using the finally block in the pseudocode in Figure 11-21, you could insert the statement If the file is open, close it as both the last statement in the try block and the second-to-last statement in the catch block, just before the program exits. However, writing code just once in a finally block is clearer and less prone to error. Java, Visual Basic, and C++ provide try and catch blocks. Java and Visual Basic also provide a finally block, but C++ does not. Many well-designed programs with one or more try blocks do not include catch blocks; instead, they contain only try-finally pairs. The finally block is used to release resources that other applications might be waiting for, such as database connections. 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. 517 Handling Exceptions Thrown from Outside Methods Handling Exceptions Thrown from Outside Methods An advantage of using object-oriented exception-handling techniques is the ability to deal with exceptions appropriately as you decide how to handle them.

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  C# Programming

  From Problem Analysis to Program Design

  • Barbara Doyle, , , (Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  . . catch . . . finally blocks. The code that might create a problem is placed in the try block. The code to deal with the problem (the exception handler) is placed in catch blocks, which are also called catch clauses . The code that you want executed regardless of whether an exception is thrown is placed in the finally block. The syntax for a try . . . catch . . . finally block is as follows: try { // Statements that might create a problem } catch [(ExceptionClassName exceptionIdentifier)] { // Exception handler statements } : // [additional catch clauses] [ finally { // Statements to be performed no matter what happens }] More than one catch clause can be included. A try block must include at least one catch clause. Notice that a square bracket follows the keyword catch to indicate that the parentheses and the argument list are optional. Omitting the argument list makes 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. Exception-Handling Techniques | 805 1 2 the catch generic —meaning any exception that is thrown is handled by executing the code within that catch block. If you include an exception type as part of the argu-ment list, only exceptions that match the type listed are handled by that catch clause. You will see examples using multiple catch clauses later in this chapter. The finally clause is also optional. It can be included if there is a segment of code that needs to be executed, no matter what.

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  C++ for Engineers and Scientists

  • Gary Bronson(Author)
  • 2012(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Recall from Section 9.1 that the code for general exception handling looks like this: try { // one or more statements, at least one of which // should throw an exception } catch( exceptionDataType parameterName ) { // one or more statements } In this code, the try block statements are executed. If no error occurs, the catch block statements are omitted, and processing continues with the statement following the catch block. However, if any statement in the try block throws an exception, the catch block with the exception data type matching the exception is executed. If no catch block is defined for a try block, a compiler error occurs. If no catch block exists that catches a thrown data type, a program crash occurs if the exception is thrown. Most times, the catch block displays an error message and terminates processing with a call to the exit() function. Program 9.3 shows the statements required to open a file in read mode and includes exception handling. 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.

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

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

    (Publisher)

  526 C H A P T E R 1 1 Exception Handling • When you think an error will occur frequently, the most efficient approach is to handle the error in the traditional way, with if statements. If an error will occur infrequently, instantiating an Exception object when needed is more efficient. In object-oriented terminology, you “try” a procedure that may not complete correctly. A method that detects an error condition or exception “throws” an exception, and the block of code that processes the error “catches” the exception. You must include at least one catch block or finally block immediately following a try block. • Every Exception object contains a ToString() method and a Message property that contains useful information about the Exception . • You can place as many statements as you need within a try block, and you can catch as many different exceptions as you want. If you try more than one statement, only the first error-generating statement throws an exception. When multiple catch blocks are present, they are examined in sequence until a match is found for the Exception type that occurred. When you list multiple catch blocks after a try block, you must be careful about their order, or some catch blocks might become unreachable. • The TryParse() methods that you can use to convert strings to other data types without causing exceptions use exception-handling techniques internally. • A finally block performs actions at the end of a try…catch sequence, whether an exception was thrown or not. • 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.

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  C++ Programming

  From Problem Analysis to Program Design

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

    (Publisher)

  6. The try block is followed by one or more catch blocks. 7. A catch block specifies the type of exception it can catch and contains an exception handler. 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. 1026 | Chapter 14: Exception Handling 8. If the heading of a catch block contains . . . (ellipsis) in place of param- eters, then this catch block can catch exceptions of all types. 9. If no exceptions are thrown in a try block, all catch blocks associated with that try block are ignored and program execution resumes after the last catch block. 10. If an exception is thrown in a try block, the remaining statements in the try block are ignored. The program searches the catch blocks, in the order they appear after the try block, and looks for an appropriate excep- tion handler. If the type of the thrown exception matches the parameter type in one of the catch blocks, then the code in that catch block executes and the remaining catch blocks after this catch block are ignored. 11. The data type of the catch block parameter specifies the type of exception that the catch block can catch. 12. A catch block can have, at most, one catch block parameter. 13. If only the data type is specified in a catch block heading, that is, if there is no catch block parameter, then the thrown value may not be accessible in the catch block exception-handling code. 14. In order for an exception to occur in a try block and be caught by a catch block, the exception must be thrown in the try block.

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  OCA: Oracle Certified Associate Java SE 8 Programmer I Study Guide

  Exam 1Z0-808

  • Jeanne Boyarsky, Scott Selikoff(Authors)
  • 2014(Publication Date)
  • Sybex

    (Publisher)

  try statement is lonely.

  Now that you know the basics, let's start adding more features to exceptions. The following sections show you how to add a finally clause to a try statement and catch different types of exceptions and describe what happens if an exception is thrown in catch or finally .

  Adding a

  finally

  Block

  The try statement also lets you run code at the end with a

  finally clause

  regardless of whether an exception is thrown. Figure 6.3 shows the syntax of a try statement with this extra functionality.

  Figure 6.3

  The syntax of a try statement with

  finally

  There are two paths through code with both a catch and a finally . If an exception is thrown, the finally block is run after the catch block. If no exception is thrown, the finally block is run after the try block completes.

  Let's go back to our young girl example, this time with finally :

  12: void explore() { 13: try { 14: seeAnimals(); 15: fall(); 16: } catch (Exception e) { 17: getHugFromDaddy(); 18: } finally { 19: seeMoreAnimals(); 20: } 21: goHome(); 22: }

  The girl falls on line 15. If she gets up by herself, the code goes on to the finally block and runs line 19. Then the try statement is over and the code proceeds on line 21. If the girl doesn't get up by herself, she throws an exception. The catch block runs and she gets a hug on line 17. Then the try statement is over and the code proceeds on line 21. Either way, the ending is the same. The finally block is executed and the try statement ends.

  On the OCA exam, a try statement must have catch and/or finally . Having both is fine. Having neither is a problem. On the OCP exam, you'll learn about a special syntax for a try statement called try-with-resources that allows neither a catch nor a finally block. On the OCA exam, you get to assume a try statement is just a regular try

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