Generating entries in a file

• A file is opened for reading by creating a FileInputStream object.

• The FileInputStream(String filename) constructor throws FileNotFoundException if the file does not exist.

• FileNotFoundException is a subclass of IOException.

• To read a file, use the read() method, which reads a byte and returns an integer value.

• read() returns -1 when the end of the file is reached and throws IOException on error.

• After use, the file must be closed with the close() method to free up system resources.

• Not closing the file may cause memory leaks.

• The example program uses read() to display the contents of a file and uses try/catch blocks to handle I/O errors.

• Note: In Java, a memory leak occurs when the program does not free up memory resources that it is no longer using, keeping these resources occupied unnecessarily. Although the language has automatic garbage collection for unreferenced objects, this collection does not directly deal with external resources such as files or network connections. If you don't close the file, system resources remain busy, degraded performance and errors and failures (when trying to open another file, for example).

• The previous example closes the flow after the try block for reading the file.

• Java allows an alternative approach: calling close() inside a finally block.

• With the finally block, the file is closed regardless of how the try block ends.

• This approach guarantees that the file will close, even if an exception occurs.

• The try block accesses the file, and finally is used exclusively to close it.

• The advantage of using the finally block is to guarantee the closure of the file, even if a non-I/O exception occurs.

• Although not critical in small programs, this approach is essential in larger programs to avoid problems.

• Using finally helps avoid the hassle of dealing with unclosed files in case of unexpected exceptions.

• Encapsulating file opening and file access in a single try block and using finally to close it is a best practice.

• This approach can simplify the code and ensure the release of resources.

• fin is initialized to null and, in the finally block, the file is only closed if fin is not null.

• This prevents close() from being called if an exception occurs when opening the file.

• The try/catch sequence can be simplified, as FileNotFoundException is a subclass of IOException.

• Catching just IOException eliminates the need to catch FileNotFoundException separately.

• In this case, the standard exception message describes the error.

...
} catch(IOException exc) {
System.out.println("I/O error: " exc);
} finally {
...

The above is the detailed content of Generating entries in a file. For more information, please follow other related articles on the PHP Chinese website!