A Survivor’s Guide to Java Program Analysis with Soot Arni Einarsson and Janus Dam Nielsen
File Operations (The Java. This class offers a rich set of static methods for reading, writing, and manipulating files and directories. The Files methods work on instances of Path objects. Before proceeding to the remaining sections, you should familiarize yourself with the following common concepts: Many of the resources that are used in this API, such as streams or channels, implement or extend the. IntroductiontoProgrammingUsingJava Version7.0,August2014 DavidJ.Eck HobartandWilliamSmithColleges This is a PDF version of a free on-line book that is available at http:// The PDF does not include.Closeable interface. A requirement of a Closeable resource is that the close method must be invoked to release the resource when no longer required. Neglecting to close a resource can have a negative implication on an application's performance. The try- with- resources statement, described in the next section, handles this step for you. With file I/O, unexpected conditions are a fact of life: a file exists (or doesn't exist) when expected, the program doesn't have access to the file system, the default file system implementation does not support a particular function, and so on. Numerous errors can be encountered. All methods that access the file system can throw an IOException. It is best practice to catch these exceptions by embedding these methods into a try- with- resources statement, introduced in the Java SE 7 release. The try- with- resources statement has the advantage that the compiler automatically generates the code to close the resource(s) when no longer required. The following code shows how this might look. Charset charset = Charset. Name(. If your code has opened any streams or channels, you should close them in a finally block. The previous example would look something like the following using the try- catch- finally approach. Charset charset = Charset. Name(. This class has some useful methods that return the file involved. File), the detailed message string. Message), the reason why the file system operation failed. Reason), and the . For example, in the following method signature, the ellipses notation after the Copy. Option argument indicates that the method accepts a variable number of arguments, or varargs, as they are typically called. Path Files. move(Path, Path, Copy. Option..). When a method accepts a varargs argument, you can pass it a comma- separated list of values or an array (Copy. Option. Either the entire operation is performed or the operation fails. This is important when you have multiple processes operating on the same area of the file system, and you need to guarantee that each process accesses a complete file. Many of the file I/O methods support the concept of method chaining. You first invoke a method that returns an object. You then immediately invoke a method on that object, which returns yet another object, and so on. Many of the I/O examples use the following technique. String value = Charset. Charset(). decode(buf). String(). User. Principal group =. File. System(). get. User. Principal. Lookup. Service(). Glob syntax follows several simple rules: An asterisk, *, matches any number of characters (including none). Two asterisks, **, works like * but crosses directory boundaries. This syntax is generally used for matching complete paths. A question mark, ?, matches exactly one character. Braces specify a collection of subpatterns. For example: \\ matches a single backslash, and \? However, if it is not sufficient for your needs, you can also use a regular expression. For more information, see the. Regular Expressions lesson. For more information about the glob sytnax, see the API specification for the. Path. Matcher method in the File. System class. The Files class is.
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