Computer Science
Java Finally
Java Finally is a block of code that is used in Java programming to ensure that a specific set of instructions are executed regardless of whether an exception is thrown or not. It is typically used to release resources that were acquired during the execution of a program.
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5 Key excerpts on "Java Finally"
- Joyce Farrell(Author)
- 2012(Publication Date)
- Cengage Learning EMEA(Publisher)
In the case of an unhandled exception, program execution stops immediately, the exception is sent to the operating system for handling, and the current method is abandoned. Likewise, the try block might contain a statement that stops program execution immediately in the programming language you are using. Additionally, the try block might correctly throw an exception to the catch block, but the catch block might contain a program-ending statement or throw an unhandled exception; either way, the program would end abruptly. In several languages, the statement that stops program execution is exit or exit() . When you include a finally block, you are assured that the finally statements will execute before the method is abandoned, even if the method concludes prematurely. For example, statements before try-catch-finally block starts try statements to try endtry catch (Exception e) actions that occur if exception was thrown endcatch finally actions that occur whether catch block executed or not endfinally statements after try-catch-finally block is complete Figure 10-10 Format of try..catch..finally sequence 381 Using the finally Block 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. programmers often use a finally block when the program uses data files that must be closed. Consider the pseudocode in Figure 10-11, which represents part of the logic for a typical file-handling program. You can avoid using a finally block, but you would need repetitious code.
eBook - PDF- Ivor Horton(Author)
- 2005(Publication Date)
- Wrox(Publisher)
However, in general it is more useful and better practice to have a catch block for each of the specific types of exceptions that a try block can throw. The finally Block The immediate nature of an exception being thrown means that execution of the try block code breaks off, regardless of the importance of the code that follows the point at which the exception was thrown. This introduces the possibility that the exception leaves things in an unsatisfactory state. You might have opened a file, for example, and because an exception was thrown, the code to close the file is not executed. The finally block provides the means for you to clean up at the end of executing a try block. You use a finally block when you need to be sure that some particular code is run before a method returns, no 350 Chapter 7 matter what exceptions are thrown within the associated try block. A finally block is always executed, regardless of whether or not exceptions are thrown during the execution of the associated try block. If a file needs to be closed, or a critical resource released, you can guarantee that it will be done if the code to do it is put in a finally block. The finally block has a very simple structure: finally { // Clean-up code to be executed last } Just like a catch block, a finally block is associated with a particular try block, and it must be located immediately following any catch blocks for the try block. If there are no catch blocks, then you posi- tion the finally block immediately after the try block. If you don’t do this, your program will not compile. Structuring a Method You’ve looked at the blocks you can include in the body of a method, but it may not always be obvious how they are combined. The first thing to get straight is that a try block plus any corresponding catch blocks and the finally block all bunch together in that order: try { // Code that may throw exceptions...
eBook - PDF- Scott Selikoff, Jeanne Boyarsky(Authors)
- 2022(Publication Date)
- Sybex(Publisher)
The finally keyword The catch block is optional when finally is used. FIGURE 11.4 The syntax of a try statement with finally Handling Exceptions 613 36: 37: try { 38: fall(); 39: } finally { 40: System.out.println(all better); 41: } The first example (lines 25–31) does not compile because the catch and finally blocks are in the wrong order. The second example (lines 33–35) does not compile because there must be a catch or finally block. The third example (lines 37–41) is just fine. The catch block is not required if finally is present. Most of the examples you encounter on the exam with finally are going to look contrived. For example, you’ll get asked questions such as what this code outputs: public static void main(String[] unused) { StringBuilder sb = new StringBuilder(); try { sb.append( t ); } catch (Exception e) { sb.append( c ); } finally { sb.append( f ); } sb.append( a ); System.out.print(sb.toString()); } The answer is tfa . The try block is executed. Since no exception is thrown, Java goes straight to the finally block. Then the code after the try statement is run. We know that this is a silly example, but you can expect to see examples like this on the exam. There is one additional rule you should know for finally blocks. If a try statement with a finally block is entered, then the finally block will always be executed, regardless of whether the code completes successfully. Take a look at the following goHome() method. Assuming an exception may or may not be thrown on line 14, what are the possible values that this method could print? Also, what would the return value be in each case? 12: int goHome() { 13: try { 14: // Optionally throw an exception here 15: System.out.print(1); 16: return -1 ; 17: } catch (Exception e) { 18: System.out.print(2); 19: return -2 ;
eBook - ePub- Prof. Sham Tickoo(Author)
- 2017(Publication Date)
- CADCIM Technologies(Publisher)
try block exists in it.If the finally clause exists in a program, it will be executed after the try /catch block, but before the statements that follow the try /catch block. The main advantage of using this clause is that the code given inside it gets executed irrespective of occurrence of an exception. The syntax for using the finally clause is as follows:finally {//Statements to be executed}The finally clause is optional and if it is used with the try block, it will be placed after the last catch block that is associated with that particular try block, as shown in the following code:try {//Statements} catch(ExceptionType obj) {//Statements} catch(ExceptionType obj) {//Statements} finally {//Statements}But, if there is no catch block associated with the try block, the finally clause is placed immediately after the try block, as given next:try {//Statements} finally( ) {//Statements}Example 6The following example illustrates the use of the finally clause. The program will calculate the square of a number that will be passed as a command-line argument by the user. Also, this program will handle the exception using the try - catch - finally mechanism and display a message on the screen.//Write a program to calculate the square of a number and also to handle an exception 1class finally_demo 2{3 public static int sqr(int n)4 {5 try6 {7 int result = n*n;8 if(result ==0)9 {10 throw new ArithmeticException(“demo”);11 }12 else13 {14 return result;15 }16 }17 finally18 {19 System.out.println(“Inside the finally block”);20 }21 }22 public static void main(String arg[ ])23 {24 int sq;25
eBook - PDF- Todd Greanier(Author)
- 2006(Publication Date)
- Sybex(Publisher)
For example, you might want to signify that a network port is unavailable or that there are not enough items in an inventory to fulfill an order. These possible error conditions can then be handled within the programs that are attempting to perform these actions. These errors can even be overcome without any user intervention whatsoever; the code can correct these errors while it is running. In other words, the exception-handling aspect of the language allows you to maintain robustness in your specific programs. Java Is Secure exception handling A form of flow control that handles pro-gram errors. In many other languages, errors are reported as a code number of some kind that is often cryptic and diffi-cult to work with. Java uses exception handling, which provides a more robust method for trapping and recovering from logical errors. One of the top features for end users of a Java application is that it can be dynam-ically downloaded from a remote location. Although this is indeed a powerful, desirable feature, a lot of risk is inherent in the process. It does not seem wise to download code from someone on the Internet and then just let it run at will on your system, does it? This is how things such as viruses and other maliciousness can invade your otherwise happy computer. Luckily, Java recognized these potential threats and incorporated a multiphase approach to ensure a high level of security. To begin with, you just learned about the robustness of the language in regard to its memory management and compile-time checking. These two features also contribute significantly to Java’s security. Because the JVM is “in charge,” it is impossible for normal Java code to cause a problem with system memory that could lead to insecure or corrupted data. It also means that pure Java code is 8 Chapter 1 unable to install a virus or worm on your system because it cannot “touch” mem-ory directly. Java security also extends to so-called foreign code.
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