(*)Garbage collector is a component that works as a janitor in JVM, responsible for keeping the memory clean to avoid memory leaks-to release the occupied but out of scope players (read objects and variables) from the playground for other players to pour in. In this article, we shall try to elaborate the way to process common sequential files through Java and some aspects of file handling APIs in general. Thus, the only way to persist data permanently is to store them somehow in the secondary storage devices such as hard disks, optical disks, pen drives, and so forth, and retrieve on demand accordingly. Variables and arrays we use for storage in code are temporary they are stored in the primary storage area (such as RAM) and live until the program terminates or garbage collector (*) sweeps the memory clean. If System.IO.File.Exists(textFilePath) = False Thenĭebug.WriteLine("File Not Found: " & textFilePath)ĭim sr As System.IO.StreamReader = System.IO.File.When talking about permanent retention of data, a common text file is the basic unit of data storage apart from using complicated database and other repositories. Private Sub ShowText(ByVal textFilePath As String) In the Do.Loop condition, the Peek method of the StreamReader determines whether there are any additional characters. The OpenText method opens the file and returns a StreamReader that reads the characters. The following example reads all lines in a text file. The following example uses a While clause instead of an Until clause, and condition is tested at the start of the loop instead of at the end. The Until clause is at the end of the loop. In the following example, the statements in the loop continue to run until the index variable is greater than 10. When used within nested Do loops, Exit Do transfers control out of the innermost loop and into the next higher level of nesting. You can include any number of Exit Do statements anywhere in a Do…Loop. One use of Exit Do is to test for a condition that could cause an endless loop, which is a loop that could run a large or even infinite number of times. You might want to exit a loop if you detect a condition that makes it unnecessary or impossible to continue iterating, such as an erroneous value or a termination request. Exit Do transfers control immediately to the statement that follows the Loop statement.Įxit Do is often used after some condition is evaluated, for example in an If.Then.Else structure. The Exit Do statement can provide an alternative way to exit a Do…Loop. It also enables you to test condition at either the start or the end of the loop. The Do.Loop structure gives you more flexibility than the While.End While Statement because it enables you to decide whether to end the loop when condition stops being True or when it first becomes True. For more information, see Nested Control Structures. You can also nest different kinds of control structures within each other. You can nest Do loops by putting one loop within another. This includes values of other data types, such as numeric types, that have been converted to Boolean. The condition usually results from a comparison of two values, but it can be any expression that evaluates to a Boolean Data Type value ( True or False). If you test at the end of the loop (in the Loop statement), the loop always runs at least one time. If you test condition at the start of the loop (in the Do statement), the loop might not run even one time. You can test condition only one time, at either the start or the end of the loop. If you give neither, the loop continues until an Exit transfer control out of the loop. You can use either While or Until to specify condition, but not both. If you want to repeat the statements a set number of times, the For.Next Statement is usually a better choice. Use a Do.Loop structure when you want to repeat a set of statements an indefinite number of times, until a condition is satisfied. Terminates the definition of the Do loop. Transfers control to the next iteration of the Do loop. One or more statements that are repeated while, or until, condition is True. If condition is Nothing, Visual Basic treats it as False. Repeat the loop until condition is False.Ĭannot be given if While is used. Starts the definition of the Do loop.Ĭannot be given if Until is used. Repeats a block of statements while a Boolean condition is True or until the condition becomes True.
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