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Java How to Program, 10/e © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Data stored in RAM is temporary It’s lost when a local variable goes out of scope or when the program terminates For long term retention of data, computers use files. Computers store files on secondary storage devices Solid state drives, hard disks, optical disks, flash drives and magnetic tapes. Data maintained in files is persistent data because it exists beyond the duration of program execution. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Ultimately, a computer processes data items as combinations of zeros and ones It’s simple and economical for engineers to build electronic devices that can assume two stable states - one representing 0 and the other representing 1. The simplest data item assumes the value 0 or the value 1. Such a data item is called a bit. Short for “binary digit” - a digit that can assume one of two values. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. 4 Programmers prefer to work with decimal digits (0–9), letters (A–Z and a–z), and special symbols (e.g., $, @, %, &, *, (, ), –, +, ", :, ? and / ). Known as characters. Character set - the set of all the characters used to write programs and represent data items. Java uses Unicode characters that are composed of two bytes, each byte is eight bits. Java type byte can be used to represent byte data. Unicode contains characters for many of the world’s languages. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. 5 Fields are composed of characters, numbers, bytes, … A field is a group of data items of the same type that conveys meaning. Data items form a data hierarchy that becomes larger and more complex in structure as we progress from bits to characters to fields, and so on. Typically, several fields compose a record (implemented as a class in Java). A record is a group of related fields. A file is a group of related records or general data. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. 6 To facilitate retrieving specific records from a file, at least one field in each record may be chosen as a record key. A record key identifies a record as belonging to a particular person or entity and is unique to each record Typically used to search and sort records. There are many ways to organize records in a file. The most common is called a sequential file, in which records are stored in order by the record key field. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. 7 A group of related data files is called a database. A collection of programs designed to create and manage databases is called a database management system (DBMS). . © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. 8 To read data from or write data to a file, we must create one of the Java stream objects and attach it to the file. A stream is a sequence of data items, usually 8-bit bytes. Java has two types of streams: an input stream and an output stream. An input stream has a source from which the data items come, and an output stream has a destination to which the data items are going. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Java views each file as a sequential stream of bytes (Fig. 15.1). Every operating system provides a mechanism to determine the end of a file, such as an end-of-file marker or a count of the total bytes in the file that is recorded in a system maintained administrative data structure. A Java program simply receives an indication from the operating system when it reaches the end of the stream © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. File streams can be used to input and output data as bits, bytes, characters, ..., objects. Streams that input and output bytes are known as byte based streams, representing data in its binary format. Streams that input and output characters are known as character based streams, representing data as a sequence of characters. Files that are created using byte based streams are referred to as binary files. Files created using character based streams are referred to as text files. Text files can be read by text editors. Binary files are read by programs that understand the specific content of the file and the ordering of that content. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Prior to using a file, Java program must open this file by creating an stream type object and associating a stream of bytes or characters with it. Streams also associate with other devices – keyboard, network, ... JVM always creates three stream objects when a program begins executing: System.in (the standard input stream object) normally inputs bytes from the keyboard. System.out (the standard output stream object) normally outputs character data to the screen. System.err (the standard error stream object) normally outputs character based error messages to the screen. Class System provides methods setIn, setOut and setErr to redirect the standard input, output and error streams, respectively. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Java programs perform file processing by using classes from package java.io and the subpackages of java.nio. Includes definitions for stream classes, e.g. FileInputStream (for byte based input from a file) FileOutputStream (for byte based output to a file) FileReader (for character based input from a file) FileWriter (for character based output to a file) You open a file by creating an object of one of these stream classes. The object’s constructor opens the file. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Class File provides information about files and directories. Character based input and output can be performed using classes Scanner and Formatter. Class Scanner is used extensively to input data from the keyboard. This class can also read data from a file. Class Formatter enables formatted data to be output to any text-based stream in a manner similar to method System.out.printf. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Java allows to perform input and output of objects or variables of primitive data types without having to worry about the details of converting such values to byte format. To perform such input and output, objects of classes ObjectInputStream and ObjectOutputStream can be used together with the byte based file stream classes FileInputStream and FileOutputStream. The complete hierarchy of classes in package java.io can be viewed in the online documentation at http://download.oracle.com/javase/8/docs/api/java/io/package -tree.html © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Java SE 8 Adds Another Type of Stream Chapter 17, Java SE 8 Lambdas and Streams, introduces a new type of stream that’s used to process collections of elements (like arrays and ArrayLists), rather than the streams of bytes we discuss in this chapter’s file processing examples. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Interfaces Path and DirectoryStream and classes Paths and Files (all from package java.nio.file) are useful for retrieving information about files and directories on disk: Path interface—Objects of classes that implement this interface represent the location of a file or directory. Path objects do not open files or provide any file processing capabilities. Paths class—Provides static methods used to get a Path object representing a file or directory location. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Files class—Provides static methods for common file and directory manipulations, such as copying files; creating and deleting files and directories; getting information about files and directories; reading the contents of files; getting objects that allow you to manipulate the contents of files and directories; and more DirectoryStream interface—Objects of classes that implement this interface enable a program to iterate through the contents of a directory. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. A file or directory’s path specifies its location on disk. The path includes some or all of the directories leading to the file or directory. An absolute path contains all directories, starting with the root directory, that lead to a specific file or directory. Every file or directory on a particular disk drive has the same root directory in its path. A relative path is “relative” to another directory—for example, a path relative to the directory in which the application began executing. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. An overloaded version of Files static method get uses a URI object to locate the file or directory. A Uniform Resource Identifier (URI) is a more general form of the Uniform Resource Locators (URLs) that are used to locate websites. On Windows platforms, the URI file://C:/data.txt identifies the file data.txt stored in the root directory of the C: drive. On UNIX/Linux/MAC platforms, the URI file:/home/student/data.txt identifies the file data.txt stored in the home directory of the user student. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. ch15\fig15_02\FileAndDirectoryInfo.java class prompts the user to enter a file or directory name, then uses classes Paths and Files and interfaces Path and DirectoryStream to output information about that file or directory. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. A separator character is used to separate directories and files in a path. On a Windows computer, the separator character is a backslash \. On a UNIX, Linux or Mac OS X system, it’s a forward slash /. Java processes both characters mostly correctly in a path name. For example, if we were to use the path c:\Program Files\Java\jdk1.6.0_11\demo/jfc which employs each separator character, Java would still process the path properly. But there may be other problems, e.g. a blank in the folder name. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. When building Strings that represent path information, a safe approach is to use File.separator to obtain the local computer’s proper separator character. This constant returns a String consisting of one character - the proper separator for the system. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Sequential access files store records in order by the record key field. Text files are human readable files. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Java imposes no structure on a file Notions such as records do not exist as part of the Java language. You must structure files to meet the requirements of your applications. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Formatter class outputs formatted String to the specified stream. The constructor with one String argument receives the name of the file, including its path. If a path is not specified, the JVM assumes that the file is in the current directory (from which the program was executed or NetBeans project directory if the program was executed inside NetBeans). If the file does not exist, it will be created. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. If an existing file is opened, its contents are truncated (discarded). ch15\TextFileApps\CreateTextFile.java © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. A SecurityException occurs if the user does not have permission to write data to the file. A FileNotFoundException occurs if the file does not exist and a new file cannot be created. static method System.exit terminates an application An int argument of 0 indicates successful program termination. A nonzero value normally indicates that an error has occurred. The argument is useful if the program is executed from a batch file on Windows or a shell script on UNIX/Linux/Mac OS X. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Scanner method hasNext determines whether the endof-file key combination has been entered. A NoSuchElementException occurs if the data being read by a Scanner method is in the wrong format or if there is no more data to input. Formatter method format works similar to System.out.printf A FormatterClosedException occurs if an attempt is made to write to a file using an already closed Formatter object. Formatter method close closes the file If method close is not called explicitly, the operating system normally will close the file when program execution terminates. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Different platforms use different line separator characters. On UNIX/Linux/Mac OS X, the line separator is a newline character ’\n’. On Windows, it is a combination of a carriage return and a line feed characters represented as “\r\n”. You can use the %n format specifier in a format control string to output a platform specific line separator. Method System.out.println outputs a platform specific line separator after its argument. Regardless of the line separator used in a text file, a Java program can still recognize the lines of text and read them. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. To read the file data back correctly, we always must know the order of the data stored and the data types! The application in Fig. 15.6 reads records from the file "clients.txt" created by the application of Section 15.4.1 and displays the record contents. ch15\TextFileApps\ReadTextFile.java © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Scanner class can be used to read data sequentially from a text file Pass File object representing file to be read to Scanner constructor. FileNotFoundException occurs if file cannot be found. Data is read from file using same methods as for keyboard input – nextInt, nextDouble, next, etc. IllegalStateException occurs if attempt is made to read from closed Scanner object. Scanner method hasNext determines whether the end-of-file key combination has been entered/reached. A NoSuchElementException occurs if the data being read by one of the Scanner methods is in the wrong format or if there is no more data to input. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. To retrieve data sequentially from a file, programs start from the beginning of the file and read all the data consecutively until the desired information is found. It might be necessary to process the file sequentially several times (from the beginning of the file) during the execution of a program. Class Scanner does not allow repositioning to the beginning of the file. The program must close the file and reopen it. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. ch15\TextFileApps\CreditInquiry.java ch15\TextFileApps\MenuOption.java © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. The data in many sequential files cannot be modified without the risk of destroying other data in the file. If the name “White” needed to be changed to “Worthington,” the old name cannot simply be overwritten, because the new name requires more space. Fields in a text file and hence records can vary in size. Records in a sequential access file are not normally updated in place. Instead, the entire file is usually rewritten. Rewriting the entire file is very inefficient to update just one record, but reasonable if a substantial number of records need to be updated. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. In text files Java data type information is being lost. To read an entire object from or write an entire object to a file, Java provides object serialization. A serialized object is represented as a sequence of bytes that includes the object’s data and its type information. After a serialized object has been written into a file, it can be read from the file and deserialized to recreate the object in memory. Java arrays are objects so, instead of processing array elements individually, it is possible to save to and read from a file the whole array with a single Java statement. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Classes ObjectInputStream and ObjectOutputStream, which implement the ObjectInput and ObjectOutput interfaces respectively, enable entire objects to be read from or written to a stream with a single method call. To use serialization with files, initialize ObjectInputStream and ObjectOutputStream objects with FileInputStream and FileOutputStream objects as constructor arguments. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. ObjectOutput interface method writeObject takes an Object instance as an argument and writes its information to an OutputStream. A class that implements ObjectOutput (such as ObjectOutputStream) declares this method and ensures that the object being output implements Serializable interface. ObjectInput interface method readObject reads and returns a reference to an Object from an InputStream. After an object has been read, its reference should be cast to the object’s actual type. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Only objects of classes that implement interface Serializable can be serialized and deserialized with ObjectOutputStream and ObjectInputStream. Interface Serializable is a tagging interface. It does not contain any methods. A class that implements Serializable is tagged as being a Serializable object. An ObjectOutputStream cannot output an object unless it is a Serializable object – the code will not compile. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. ch15\SerializationApps\Account.java ch15\SerializationApps\CreateSequentialFile.java © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. In a class that implements Serializable interface, every data field must be Serializable. Any one that is not must be declared transient so it will be ignored during the serialization process. All primitive type variables are serializable. For reference type variables, check the class’s documentation (and possibly its superclasses) to ensure that the type is Serializable. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. The program in Fig. 15.11 reads records from a file created by the program in Section 15.5.1 and displays the contents. ch15\SerializationApps\ReadSequentialFile.java © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. ObjectInputStream method readObject reads an Object from a file. Method readObject throws an EOFException if an attempt is made to read beyond the end of the file. Casting of the return value of readObject throws a ClassNotFoundException if the class for the object being read is not castable to the selected type. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Class JFileChooser displays a dialog that enables the user to easily select files or directories. ch15\fig15_12_13\JFileChooserDemo.java ch15\fig15_12_13\JFileChooserTest.java © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. JFileChooser method setFileSelectionMode specifies what the user can select from the fileChooser. JFileChooser static constant FILES_AND_DIRECTORIES indicates that files and directories can be selected. Other static constants include FILES_ONLY (the default) and DIRECTORIES_ONLY. Method showOpenDialog displays a JFileChooser dialog titled Open, with Open and Cancel buttons (to open a file/directory or dismiss the dialog, respectively). JFileChooser dialog is a modal dialog. Method showOpenDialog returns an integer specifying which button (Open or Cancel) the user clicked to close the dialog. CANCEL_OPTION constant specifies that user clicked Cancel button JFileChooser method getSelectedFile returns the selected file as a File object. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. This section overviews additional interfaces and classes (from package java.io) for byte based input and output streams and character based input and output streams. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. InputStream and OutputStream are abstract classes that declare methods for performing byte based input and output, respectively. Pipes are synchronized communication channels between threads. PipedOutputStream (a subclass of OutputStream) and PipedInputStream (a subclass of InputStream) establish pipes between two threads in a program. One thread sends data to another by writing to a PipedOutputStream. The target thread reads information from the pipe via a PipedInputStream. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. A FilterInputStream filters an InputStream, and a FilterOutputStream filters an OutputStream. Filtering means simply that the filter stream provides additional functionality, such as aggregating data bytes into meaningful primitive type units. FilterInputStream and FilterOutputStream are typically extended, so some of their filtering capabilities are provided by their subclasses. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. A PrintStream (a subclass of FilterOutputStream) performs text output to the specified stream. System.out and System.err are PrintStream instances. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Usually, programs read data as aggregates of bytes that form ints, floats, doubles, and so on. Java programs can use several classes to input and output data in aggregate form. Interface DataInput describes methods for reading primitive types from an input stream. Classes DataInputStream and RandomAccessFile each implement this interface to read sets of bytes and process them as primitive type values. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Interface DataOutput describes a set of methods for writing primitive types to an output stream. Classes DataOutputStream (a subclass of FilterOutputStream) and RandomAccessFile each implement this interface to write primitive type values as bytes. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Buffering is an I/O performance enhancement technique. With a BufferedOutputStream, each output operation is directed to an in-memory buffer holds the data of many output operations. Transfer to the output device is performed in one large physical output operation each time the buffer fills. The output operations directed to the output buffer in memory are often called logical output operations. A partially filled buffer can be forced out to the device at any time by invoking the stream object’s flush method. Using buffering can greatly increase the performance of an application. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. With a BufferedInputStream, many “logical” chunks of data from a file are read as one large physical input operation into a memory buffer. As a program requests each new chunk of data, it’s taken from the buffer. This procedure is sometimes referred to as a logical input operation. When the buffer is empty, the next actual physical input operation from the input device is performed. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. Java stream I/O includes capabilities for inputting from byte arrays in memory and outputting to byte arrays in memory. A ByteArrayInputStream (a subclass of InputStream) reads from a byte array in memory. A ByteArrayOutputStream (a subclass of OutputStream) outputs to a byte array in memory. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. A SequenceInputStream (a subclass of InputStream) logically concatenates several InputStreams. The program sees the group of streams as one continuous InputStream. When the program reaches the end of one input stream, that stream closes, and the next stream in the sequence opens automatically. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. The Reader and Writer abstract classes represent Unicode two byte, character based streams. Most of the byte based streams have corresponding character based concrete Reader or Writer classes. Classes BufferedReader (a subclass of abstract class Reader) and BufferedWriter (a subclass of abstract class Writer) enable buffering for character based streams. Classes CharArrayReader and CharArrayWriter read and write, respectively, a stream of characters from/to a char array. A LineNumberReader (a subclass of BufferedReader) is a buffered character stream that keeps track of the number of lines read. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. An InputStream can be converted to a Reader via class InputStreamReader. An OuputStream can be converted to a Writer via class OutputStreamWriter. Classes FileReader and class FileWriter read characters from and write characters to a file. Classes PipedReader and class PipedWriter implement piped character streams for transferring data between threads. Classes StringReader and StringWriter read characters from and write characters to Strings. A PrintWriter writes characters to a stream. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. File I/O exception handling and file close are a must – always use try-catch-finally or try-with-resources blocks. All Java file I/O exceptions are checked exceptions – your code won’t compile if these exceptions are not properly handled. Correct file I/O sequence: Open file. If failure stop and try to recover. Read or write. Close file. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. 11 1 Don’t ever try to read from/write to a file if file open failed. Files must be always closed explicitly by the program to release resources ASAP. Always place the call to the close method in the finally block or use try-with-resources technique. To read from a file, one needs to know how the file was created and written to. Always take the write operation into consideration when designing the file read code. Java file I/O uses decorator pattern to simplify code design – an instance of one class can be passed as a constructor argument when creating instances of other I/O classes. © Copyright 1992-2015 by Pearson Education, Inc. All Rights Reserved. 11 2
