chapter 15: input and output f stream classes f processing external files f data streams f print...
TRANSCRIPT
Chapter 15: Input and Output Stream ClassesStream Classes Processing External FilesProcessing External Files Data StreamsData Streams Print StreamsPrint Streams Buffered StreamsBuffered Streams Use JFileChooser Use JFileChooser Text Input and Output on the ConsoleText Input and Output on the Console Random Access FilesRandom Access Files Parsing Text FilesParsing Text Files
Streams A A streamstream is an abstraction of the continuous one- is an abstraction of the continuous one-
way flow of data. way flow of data.
Program
Output Stream
File
Input Stream
Stream Classes The stream classes can be categorized into two The stream classes can be categorized into two
types: types: byte streamsbyte streams and and character streamscharacter streams..
The InputStream/OutputStream class is theThe InputStream/OutputStream class is theroot of all byte stream classes, and the root of all byte stream classes, and the Reader/Writer class is the root of all character Reader/Writer class is the root of all character stream classes. stream classes.
The subclasses of InputStream/OutputStream The subclasses of InputStream/OutputStream are analogous to the subclasses of are analogous to the subclasses of Reader/WriterReader/Writer..
Byte Stream Classes
InputStream
OutputStream
RandomAccessFile
Object
PipeOutputStream
SequenceInputStream
StringBufferInputStream
ByteArrayOutputStream
ObjectOutputStream
FilterOutputStream
FileOutputStream
PipedInputStream
PushBackInputStream
BufferedInputStream
LineNumberInputStream
DataInputStream
BufferedOutputStream
DataOutputStream
PrintStream
ObjectInputStream
FilterInputStream
FileInputStream
ByteArrayInputStreamInputData
OutputData
ObjectOutput
ObjectInput
Character Stream Classes
Reader
Writer
StreamTokenizer
Object
PrintWriter
BufferedWriter
CharArrayWriter
PipedWriter
FilterWriter
PipedReader
LineNumberReader
FileReader
PushBackReader
FileWriter
StringWriter
StringReader
InputStreamReader
CharArrayReader
BufferedReader
FilterReader
OutputStreamWriter
InputStream abstract int read() throws IOExceptionabstract int read() throws IOException
Return a byte [0..255] or –1 (EOF)Return a byte [0..255] or –1 (EOF)
int read(byte b[]) throws IOExceptionint read(byte b[]) throws IOException
Read bytes into array and return b.lengthRead bytes into array and return b.length
void close() throws IOExceptionvoid close() throws IOException
Int available() throws IOExceptionInt available() throws IOException
Return the number of bytes to be readReturn the number of bytes to be read
long skip(long n) throws IOExceptionlong skip(long n) throws IOException
Skip over n bytesSkip over n bytes
Reader
The The ReaderReader class is similar to the InputStream class is similar to the InputStream class. The methods in class. The methods in ReaderReader are subject to are subject to character interpretation.character interpretation.
abstract int read() throws IOException
int read(char b[]) throws IOException
void close() throws IOException
long skip(long n) throws IOException
Note that if no data are available, it blocks the thread from executing next statement.
OutputStream
abstract void write(int b) throws IOExceptionabstract void write(int b) throws IOException
void write(byte[] b) throws IOExceptionvoid write(byte[] b) throws IOException
void close() throws IOExceptionvoid close() throws IOException
void flush() throws IOExceptionvoid flush() throws IOException
Writer
abstract void write(int b) throws IOExceptionabstract void write(int b) throws IOException
void write(char[] b) throws IOExceptionvoid write(char[] b) throws IOException
void close() throws IOExceptionvoid close() throws IOException
void flush() throws IOExceptionvoid flush() throws IOException
Processing External Files You must use file streams to read from or write You must use file streams to read from or write to a disk file. to a disk file. You can use You can use FileInputStreamFileInputStream or or FileOutputStreamFileOutputStream for byte streams, and you can for byte streams, and you can use use FileReaderFileReader or or FileWriterFileWriter for character for character streams. streams.
File I/O Stream Constructors
Constructing instances of Constructing instances of FileInputStreamFileInputStream, , FileOutputStreamFileOutputStream, , FileReaderFileReader, and , and FileWriter FileWriter from file from file names:names:
FileInputStream infile = new FileInputStream("in.dat");
FileOutputStream outfile = new FileOutputStream("out.dat");
FileReader infile = new FileReader("in.dat");
FileWriter outfile = new FileWriter("out.dat");
Example 15.1Processing External Files
CopyFileUsingByteStreamCopyFileUsingByteStream
RunRun
Click the Run button to access the DOS prompt; then type java CopyFileUsingByteStream ButtonDemo.java t.java and press Enter. (If working from the CD, add a path to the hard disk or floppy disk drive for t.java.)
Data Streams
The data streams (The data streams (DataInputStreamDataInputStream and and DataOutputStreamDataOutputStream) read and write Java primitive ) read and write Java primitive types in a machine-independent fashion, which types in a machine-independent fashion, which enables you to write a data file in one machine enables you to write a data file in one machine and read it on another machine that has a and read it on another machine that has a different operating system or file structure. different operating system or file structure.
DataInputStream Methods int readByte() throws IOExceptionint readByte() throws IOException
int readShort() throws IOExceptionint readShort() throws IOException
int readInt() throws IOExceptionint readInt() throws IOException
int readLong() throws IOExceptionint readLong() throws IOException
float readFloat() throws IOExceptionfloat readFloat() throws IOException
double readDouble() throws IOExceptiondouble readDouble() throws IOException
char readChar() throws IOExceptionchar readChar() throws IOException
boolean readBoolean() throwsboolean readBoolean() throwsIOExceptionIOException
String readUTF() throws IOExceptionString readUTF() throws IOException
DataOutputStream Methods void writeByte(byte b) throws IOException void writeByte(byte b) throws IOException
void writeShort(short s) throws IOException void writeShort(short s) throws IOException
void writeInt(int i) throws IOException void writeInt(int i) throws IOException
void writeLong(long l) throws IOException void writeLong(long l) throws IOException
void writeFloat(float f) throws IOException void writeFloat(float f) throws IOException
void writeDouble(double d) throws IOException void writeDouble(double d) throws IOException
void writeChar(char c) throws IOException void writeChar(char c) throws IOException
void writeBoolean(boolean b) throws IOExceptionvoid writeBoolean(boolean b) throws IOException
void writeBytes(String l) throws IOExceptionvoid writeBytes(String l) throws IOException
void writeChars(String l) throws IOExceptionvoid writeChars(String l) throws IOException
void writeUTF(String l) throws IOException void writeUTF(String l) throws IOException
Data I/O Stream Constructors DataInputStream infile = newDataInputStream infile = new
DataInputStream(new FileInputStream("in.dat"));DataInputStream(new FileInputStream("in.dat"));Creates an input file for in.dat.Creates an input file for in.dat.
DataOutputStream outfile = newDataOutputStream outfile = newDataOutputStream(new FileOutputStream("out.dat"));DataOutputStream(new FileOutputStream("out.dat"));Creates an output file for out.dat.Creates an output file for out.dat.
Example 15.2Using Data Streams
TestDataStreamsTestDataStreams
RunRun
Click the Run button to access the DOS prompt; then type java TestDataStreams and press Enter. (Note: You cannot run this from the CD; the program writes to disk.)
Print Streams
The data output stream outputs a binary The data output stream outputs a binary representation of data, so you cannot view its representation of data, so you cannot view its contents as text. In Java, you can use print contents as text. In Java, you can use print streams to output data into files. These files can streams to output data into files. These files can be viewed as text.be viewed as text.
The The PrintStreamPrintStream and and PrintWriterPrintWriter classes provide classes provide this functionality.this functionality.
PrintWriter Constructors PrintWriter(Writer out)PrintWriter(Writer out)
PrintWriter(Writer out, boolean autoFlush)PrintWriter(Writer out, boolean autoFlush)
PrintWriter(OutputStream out)PrintWriter(OutputStream out)
PrintWriter(OutputStream out, boolean PrintWriter(OutputStream out, boolean autoFlush)autoFlush)
PrintWriter Methods void print(Object o)void print(Object o) void print(String s)void print(String s) void println(String s)void println(String s) void print(char c)void print(char c) void print(char[] cArray)void print(char[] cArray) void print(int i)void print(int i) void print(long l)void print(long l) void print(float f)void print(float f) void print(double d)void print(double d) void print(boolean b)void print(boolean b)
Example 15.3Using Print Streams
RunRun
TestPrintWritersTestPrintWriters
Click the Run button to access the DOS prompt; then type java TestPrintWriters t.dat and press Enter. (Note: You cannot run this from the CD; the program writes to disk.)
Buffered Streams
Java introduces buffered streams that speed Java introduces buffered streams that speed up input and output by reducing the number of up input and output by reducing the number of reads and writes. In the case of input, a reads and writes. In the case of input, a bunch of data is read all at once instead of bunch of data is read all at once instead of one byte at a time. In the case of output, data one byte at a time. In the case of output, data are first cached into a buffer, then written all are first cached into a buffer, then written all together to the file. together to the file.
Using buffered streams is highly Using buffered streams is highly recommended.recommended.
Buffered Stream Constructors BufferedInputStream (InputStream in) BufferedInputStream (InputStream in)
Default buffer size = 512 bytesDefault buffer size = 512 bytes
BufferedInputStream (InputStream in, int bufferSize) BufferedInputStream (InputStream in, int bufferSize)
BufferedOutputStream (OutputStream in) BufferedOutputStream (OutputStream in)
BufferedOutputStream (OutputStream in, int bufferSize)BufferedOutputStream (OutputStream in, int bufferSize)
BufferedReader(Reader in)BufferedReader(Reader in)
Default buffer size = 512 charsDefault buffer size = 512 chars
BufferedReader(Reader in, int bufferSize)BufferedReader(Reader in, int bufferSize)
BufferedWriter(Writer out)BufferedWriter(Writer out)
BufferedWriter(Writer out, int bufferSize)BufferedWriter(Writer out, int bufferSize)
Example 15.4Displaying a File in a Text Area
Objective: View a file in a text area. The user Objective: View a file in a text area. The user enters a filename in a text field and clicks the enters a filename in a text field and clicks the View button; the file is then displayed in a View button; the file is then displayed in a text area.text area.
ViewFileViewFile
RunRun
JFileChooser
public JFileChooser()public JFileChooser() public JFileChooser(String currentDirPath)public JFileChooser(String currentDirPath) public JFileChooser(File currentDirectory)public JFileChooser(File currentDirectory) File selectedFileFile selectedFile File[] selectedFilesFile[] selectedFiles boolean multiSelectionEnabledboolean multiSelectionEnabled File currentDirectoryFile currentDirectory public int showOpenDialog(Component pnt)public int showOpenDialog(Component pnt)
Example 15.5Using File Dialogs Objective: Create a simple notepad using Objective: Create a simple notepad using
JFileChooserJFileChooser to open and save files. The to open and save files. The notepad enables the user to open an existing notepad enables the user to open an existing file, edit the file, and save the note into the file, edit the file, and save the note into the current file or to a specified file. You can current file or to a specified file. You can display and edit the file in a text area.display and edit the file in a text area.
RunRunFileDialogDemoFileDialogDemo
Note: You cannot run this from the CD; the programwrites to disk.
Text Input and Output on the Consoles
There are two types of interactive I/O. There are two types of interactive I/O. Text interactive I/O: simple input from the Text interactive I/O: simple input from the keyboard and simple output in a pure text form. keyboard and simple output in a pure text form. Graphical interactive I/O: input from various Graphical interactive I/O: input from various input devices and output to a graphical input devices and output to a graphical environment on frames and applets. environment on frames and applets.
Console Output/Input
To perform console output, you can use any To perform console output, you can use any of the methods for PrintStream in System.out. of the methods for PrintStream in System.out. Keyboard input is not directly supported in Keyboard input is not directly supported in Java. See MyInput.JavaJava. See MyInput.Java
call readString() to get a stringcall readString() to get a string parse the string to byte, short, int, float, …parse the string to byte, short, int, float, …
MyInputMyInput
Object Streams
Object streams enable you to perform input Object streams enable you to perform input and output at the object level. and output at the object level.
To enable an object to be read or write, the To enable an object to be read or write, the object's defining class has to implement the object's defining class has to implement the java.io.Serializablejava.io.Serializable interface or the interface or the java.io.Externalizablejava.io.Externalizable interface. interface.
The Serializable Interface
The The SerializableSerializable interface is a marker interface is a marker interface. It has no methods, so you don't interface. It has no methods, so you don't need to add additional code in your class that need to add additional code in your class that implements implements SerializableSerializable..
Implementing this interface enables the Java Implementing this interface enables the Java serialization mechanism to automate the serialization mechanism to automate the process of storing the objects and arrays. process of storing the objects and arrays.
The Object Streams
Use the ObjectOutputStream class for Use the ObjectOutputStream class for storing/writing objects (object serialization) and storing/writing objects (object serialization) and Use the ObjectInputStream class for Use the ObjectInputStream class for restoring/reading objects (object deserialization) . restoring/reading objects (object deserialization) . These two classes are built upon several other These two classes are built upon several other classes. (see next page)classes. (see next page) Note that all JavaBeans components implement Note that all JavaBeans components implement Serializable.Serializable.
The ObjectOutput and ObjectInput Streams
Object
OutputStream
DataOutput ObjectOutput
ObjectOutputStream
ObjectStreamConstants
InputStream ObjectInputStream
DataIntput ObjectIntput
Example 15.6Testing Object Streams
Objective: Objective: Stores objects of MessagePanel and Stores objects of MessagePanel and Date, and Restores these objects.Date, and Restores these objects.
RunRunObjectStreamDemoObjectStreamDemo
Note: You cannot run this from the CD; the programwrites to disk.
Random Access Files Java provides the Java provides the RandomAccessFileRandomAccessFile class to class to
allow a file to be read and updated at the allow a file to be read and updated at the same time. same time.
The The RandomAccessFileRandomAccessFile class extends class extends ObjectObject and implements and implements DataInputDataInput and and DataOutputDataOutput interfaces.interfaces.
RandomAccessFile MethodsMany methods in Many methods in RandomAccessFileRandomAccessFile are the same as those are the same as those in in DataInputStreamDataInputStream and and DataOutputStreamDataOutputStream. For example, . For example, readInt()readInt(), , readLong()readLong(), , writeDouble()writeDouble(), , readLine()readLine(), , writeInt()writeInt(), and , and writeLong()writeLong() can be used in data input stream or data output can be used in data input stream or data output stream as well as in stream as well as in RandomAccessFileRandomAccessFile streams. streams.
RandomAccessFile Methods, cont.
void seek(long pos) throws IOException;void seek(long pos) throws IOException;
Sets the offset from the beginning of the Sets the offset from the beginning of the RandomAccessFileRandomAccessFile stream to where the next read stream to where the next reador write occurs.or write occurs.
long getFilePointer() IOException;long getFilePointer() IOException;
Returns the current offset, in bytes, from theReturns the current offset, in bytes, from thebeginning of the file to where the next readbeginning of the file to where the next reador write occurs.or write occurs.
RandomAccessFile Methods, cont.
long length()IOExceptionlong length()IOException
Returns the length of the file.Returns the length of the file.
final void writeChar(int v) throws IOExceptionfinal void writeChar(int v) throws IOException
Writes a character to the file as a two-byte Writes a character to the file as a two-byte Unicode, with the high byte written first.Unicode, with the high byte written first.
final void writeChars(String s)final void writeChars(String s)throws IOExceptionthrows IOException
Writes a string to the file as a sequence ofWrites a string to the file as a sequence ofcharacters.characters.
RandomAccessFile Constructor
RandomAccessFile raf =RandomAccessFile raf =new RandomAccessFile("test.dat", "rw"); //allows new RandomAccessFile("test.dat", "rw"); //allows read and writeread and write
RandomAccessFile raf =RandomAccessFile raf =new RandomAccessFile("test.dat", "r"); //read new RandomAccessFile("test.dat", "r"); //read onlyonly
Example 15. 7 Using Random Access Files
Objective: Create a program that registers Objective: Create a program that registers students and displays student information. students and displays student information.
RunRun
TestRandomAccessFileTestRandomAccessFile
Note: You cannot run this from the CD; the programwrites to disk.
Parsing Text Files (Optional) The The StreamTokenizerStreamTokenizer class lets you take an class lets you take an input stream and parse it into words, which input stream and parse it into words, which are known as are known as tokenstokens. . The tokens are read one at a time. The tokens are read one at a time. The following is the The following is the StreamTokenizerStreamTokenizer constructor:constructor:
StreamTokenizer st = StreamTokenizer(Reader is) StreamTokenizer st = StreamTokenizer(Reader is)
StreamTokenizer Constants TT_WORDTT_WORD
The token is a word.The token is a word.
TT_NUMBERTT_NUMBER
The token is a number.The token is a number.
TT_EOLTT_EOL
The end of the line has been read.The end of the line has been read.
TT_EOFTT_EOF
The end of the file has been read.The end of the file has been read.
StreamTokenizer Variables int ttypeint ttype
Contains the current token type, which matches Contains the current token type, which matches one of the constants listed on the preceding slide.one of the constants listed on the preceding slide.
double nvaldouble nvalContains the value of the current token if that Contains the value of the current token if that token is a number.token is a number.
String svalString svalContains a string that gives theContains a string that gives thecharacters of the current token if thatcharacters of the current token if thattoken is a word. token is a word.
StreamTokenizer Methods public int nextToken() throws IOExceptionpublic int nextToken() throws IOException
Parses the next token from the input stream of this Parses the next token from the input stream of this StreamTokenizer.StreamTokenizer.
The type of the next token is returned in the ttype field. The type of the next token is returned in the ttype field.
If ttype == TT_WORD, the token is storedIf ttype == TT_WORD, the token is storedin sval; in sval;
if ttype == TT_NUMBER, the token is stored in nval.if ttype == TT_NUMBER, the token is stored in nval.