java.io

Class DataInputStream

Implemented Interfaces:
AutoCloseable, Closeable, DataInput

public class DataInputStream
extends FilterInputStream
implements DataInput

This subclass of FilteredInputStream implements the DataInput interface that provides method for reading primitive Java data types from a stream.
See Also:
DataInput

Field Summary

Fields inherited from class java.io.FilterInputStream

in

Constructor Summary

DataInputStream(InputStream in)
This constructor initializes a new DataInputStream to read from the specified subordinate stream.

Method Summary

int
read(byte[] b)
This method reads bytes from the underlying stream into the specified byte array buffer.
int
read(byte[] b, int off, int len)
This method reads bytes from the underlying stream into the specified byte array buffer.
boolean
readBoolean()
This method reads a Java boolean value from an input stream.
byte
readByte()
This method reads a Java byte value from an input stream.
char
readChar()
This method reads a Java char value from an input stream.
double
readDouble()
This method reads a Java double value from an input stream.
float
readFloat()
This method reads a Java float value from an input stream.
void
readFully(byte[] b)
This method reads raw bytes into the passed array until the array is full.
void
readFully(byte[] buf, int offset, int len)
This method reads raw bytes into the passed array buf starting offset bytes into the buffer.
int
readInt()
This method reads a Java int value from an input stream It operates by reading four bytes from the stream and converting them to a single Java int.
String
readLine()
Deprecated.
long
readLong()
This method reads a Java long value from an input stream It operates by reading eight bytes from the stream and converting them to a single Java long.
short
readShort()
This method reads a signed 16-bit value into a Java in from the stream.
String
readUTF()
This method reads a String from an input stream that is encoded in a modified UTF-8 format.
static String
readUTF(DataInput in)
This method reads a String encoded in UTF-8 format from the specified DataInput source.
int
readUnsignedByte()
This method reads 8 unsigned bits into a Java int value from the stream.
int
readUnsignedShort()
This method reads 16 unsigned bits into a Java int value from the stream.
int
skipBytes(int n)
This method attempts to skip and discard the specified number of bytes in the input stream.

Methods inherited from class java.io.FilterInputStream

available, close, mark, markSupported, read, read, read, reset, skip

Methods inherited from class java.io.InputStream

available, close, mark, markSupported, read, read, read, reset, skip

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

DataInputStream

public DataInputStream(InputStream in)
This constructor initializes a new DataInputStream to read from the specified subordinate stream.
Parameters:
in - The subordinate InputStream to read from

Method Details

read

public final int read(byte[] b)
            throws IOException
This method reads bytes from the underlying stream into the specified byte array buffer. It will attempt to fill the buffer completely, but may return a short count if there is insufficient data remaining to be read to fill the buffer.
Overrides:
read in interface FilterInputStream
Parameters:
b - The buffer into which bytes will be read.
Returns:
The actual number of bytes read, or -1 if end of stream reached before reading any bytes.
Throws:
IOException - If an error occurs.

read

public final int read(byte[] b,
                      int off,
                      int len)
            throws IOException
This method reads bytes from the underlying stream into the specified byte array buffer. It will attempt to read len bytes and will start storing them at position off into the buffer. This method can return a short count if there is insufficient data remaining to be read to complete the desired read length.
Overrides:
read in interface FilterInputStream
Parameters:
b - The buffer into which bytes will be read.
off - The offset into the buffer to start storing bytes.
len - The requested number of bytes to read.
Returns:
The actual number of bytes read, or -1 if end of stream reached before reading any bytes.
Throws:
IOException - If an error occurs.

readBoolean

public final boolean readBoolean()
            throws IOException
This method reads a Java boolean value from an input stream. It does so by reading a single byte of data. If that byte is zero, then the value returned is false. If the byte is non-zero, then the value returned is true.

This method can read a boolean written by an object implementing the writeBoolean() method in the DataOutput interface.

Specified by:
readBoolean in interface DataInput
Returns:
The boolean value read
Throws:
IOException - If any other error occurs

readByte

public final byte readByte()
            throws IOException
This method reads a Java byte value from an input stream. The value is in the range of -128 to 127.

This method can read a byte written by an object implementing the writeByte() method in the DataOutput interface.

Specified by:
readByte in interface DataInput
Returns:
The byte value read
Throws:
IOException - If any other error occurs

readChar

public final char readChar()
            throws IOException
This method reads a Java char value from an input stream. It operates by reading two bytes from the stream and converting them to a single 16-bit Java char. The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 and byte2 represent the first and second byte read from the stream respectively, they will be transformed to a char in the following manner:

(char)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)

This method can read a char written by an object implementing the writeChar() method in the DataOutput interface.

Specified by:
readChar in interface DataInput
Returns:
The char value read
Throws:
IOException - If any other error occurs

readDouble

public final double readDouble()
            throws IOException
This method reads a Java double value from an input stream. It operates by first reading a long value from the stream by calling the readLong() method in this interface, then converts that long to a double using the longBitsToDouble method in the class java.lang.Double

This method can read a double written by an object implementing the writeDouble() method in the DataOutput interface.

Specified by:
readDouble in interface DataInput
Returns:
The double value read
Throws:
IOException - If any other error occurs

readFloat

public final float readFloat()
            throws IOException
This method reads a Java float value from an input stream. It operates by first reading an int value from the stream by calling the readInt() method in this interface, then converts that int to a float using the intBitsToFloat method in the class java.lang.Float

This method can read a float written by an object implementing the writeFloat() method in the DataOutput interface.

Specified by:
readFloat in interface DataInput
Returns:
The float value read
Throws:
IOException - If any other error occurs

readFully

public final void readFully(byte[] b)
            throws IOException
This method reads raw bytes into the passed array until the array is full. Note that this method blocks until the data is available and throws an exception if there is not enough data left in the stream to fill the buffer. Note also that zero length buffers are permitted. In this case, the method will return immediately without reading any bytes from the stream.
Specified by:
readFully in interface DataInput
Parameters:
b - The buffer into which to read the data
Throws:
IOException - If any other error occurs

readFully

public final void readFully(byte[] buf,
                            int offset,
                            int len)
            throws IOException
This method reads raw bytes into the passed array buf starting offset bytes into the buffer. The number of bytes read will be exactly len. Note that this method blocks until the data is available and throws an exception if there is not enough data left in the stream to read len bytes. Note also that zero length buffers are permitted. In this case, the method will return immediately without reading any bytes from the stream.
Specified by:
readFully in interface DataInput
Parameters:
buf - The buffer into which to read the data
offset - The offset into the buffer to start storing data
len - The number of bytes to read into the buffer
Throws:
IOException - If any other error occurs

readInt

public final int readInt()
            throws IOException
This method reads a Java int value from an input stream It operates by reading four bytes from the stream and converting them to a single Java int. The bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 through byte4 represent the first four bytes read from the stream, they will be transformed to an int in the following manner:

(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) + ((byte3 & 0xFF)<< 8) + (byte4 & 0xFF)))

The value returned is in the range of -2147483648 to 2147483647.

This method can read an int written by an object implementing the writeInt() method in the DataOutput interface.

Specified by:
readInt in interface DataInput
Returns:
The int value read
Throws:
IOException - If any other error occurs

readLine

public final String readLine()
            throws IOException

Deprecated.

This method reads the next line of text data from an input stream. It operates by reading bytes and converting those bytes to char values by treating the byte read as the low eight bits of the char and using 0 as the high eight bits. Because of this, it does not support the full 16-bit Unicode character set.

The reading of bytes ends when either the end of file or a line terminator is encountered. The bytes read are then returned as a String A line terminator is a byte sequence consisting of either \r, \n or \r\n. These termination charaters are discarded and are not returned as part of the string.

This method can read data that was written by an object implementing the writeLine() method in DataOutput.

Specified by:
readLine in interface DataInput
Returns:
The line read as a String
Throws:
IOException - If an error occurs
See Also:
DataOutput

readLong

public final long readLong()
            throws IOException
This method reads a Java long value from an input stream It operates by reading eight bytes from the stream and converting them to a single Java long. The bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 through byte8 represent the first eight bytes read from the stream, they will be transformed to an long in the following manner:

(long)(((byte1 & 0xFF) << 56) + ((byte2 & 0xFF) << 48) + ((byte3 & 0xFF) << 40) + ((byte4 & 0xFF) << 32) + ((byte5 & 0xFF) << 24) + ((byte6 & 0xFF) << 16) + ((byte7 & 0xFF) << 8) + (byte8 & 0xFF)))

The value returned is in the range of -9223372036854775808 to 9223372036854775807.

This method can read an long written by an object implementing the writeLong() method in the DataOutput interface.

Specified by:
readLong in interface DataInput
Returns:
The long value read
Throws:
IOException - If any other error occurs

readShort

public final short readShort()
            throws IOException
This method reads a signed 16-bit value into a Java in from the stream. It operates by reading two bytes from the stream and converting them to a single 16-bit Java short. The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 and byte2 represent the first and second byte read from the stream respectively, they will be transformed to a short. in the following manner:

(short)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF))

The value returned is in the range of -32768 to 32767.

This method can read a short written by an object implementing the writeShort() method in the DataOutput interface.

Specified by:
readShort in interface DataInput
Returns:
The short value read
Throws:
IOException - If any other error occurs

readUTF

public final String readUTF()
            throws IOException
This method reads a String from an input stream that is encoded in a modified UTF-8 format. This format has a leading two byte sequence that contains the remaining number of bytes to read. This two byte sequence is read using the readUnsignedShort() method of this interface.

After the number of remaining bytes have been determined, these bytes are read an transformed into char values. These char values are encoded in the stream using either a one, two, or three byte format. The particular format in use can be determined by examining the first byte read.

If the first byte has a high order bit of 0, then that character consists on only one byte. This character value consists of seven bits that are at positions 0 through 6 of the byte. As an example, if byte1 is the byte read from the stream, it would be converted to a char like so:

(char)byte1

If the first byte has 110 as its high order bits, then the character consists of two bytes. The bits that make up the character value are in positions 0 through 4 of the first byte and bit positions 0 through 5 of the second byte. (The second byte should have 10 as its high order bits). These values are in most significant byte first (i.e., "big endian") order.

As an example, if byte1 and byte2 are the first two bytes read respectively, and the high order bits of them match the patterns which indicate a two byte character encoding, then they would be converted to a Java char like so:

(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))

If the first byte has a 1110 as its high order bits, then the character consists of three bytes. The bits that make up the character value are in positions 0 through 3 of the first byte and bit positions 0 through 5 of the other two bytes. (The second and third bytes should have 10 as their high order bits). These values are in most significant byte first (i.e., "big endian") order.

As an example, if byte1 byte2 and byte3 are the three bytes read, and the high order bits of them match the patterns which indicate a three byte character encoding, then they would be converted to a Java char like so:

(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) | (byte3 & 0x3F))

Note that all characters are encoded in the method that requires the fewest number of bytes with the exception of the character with the value of \u0000 which is encoded as two bytes. This is a modification of the UTF standard used to prevent C language style NUL values from appearing in the byte stream.

This method can read data that was written by an object implementing the writeUTF() method in DataOutput

Specified by:
readUTF in interface DataInput
Returns:
The String read
Throws:
IOException - If any other error occurs

readUTF

public static final String readUTF(DataInput in)
            throws IOException
This method reads a String encoded in UTF-8 format from the specified DataInput source.
Parameters:
in - The DataInput source to read from
Returns:
The String read from the source
Throws:
IOException - If an error occurs

readUnsignedByte

public final int readUnsignedByte()
            throws IOException
This method reads 8 unsigned bits into a Java int value from the stream. The value returned is in the range of 0 to 255.

This method can read an unsigned byte written by an object implementing the writeUnsignedByte() method in the DataOutput interface.

Specified by:
readUnsignedByte in interface DataInput
Returns:
The unsigned bytes value read as a Java int.
Throws:
IOException - If any other error occurs

readUnsignedShort

public final int readUnsignedShort()
            throws IOException
This method reads 16 unsigned bits into a Java int value from the stream. It operates by reading two bytes from the stream and converting them to a single Java int The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering.

As an example, if byte1 and byte2 represent the first and second byte read from the stream respectively, they will be transformed to an int in the following manner:

(int)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))

The value returned is in the range of 0 to 65535.

This method can read an unsigned short written by an object implementing the writeUnsignedShort() method in the DataOutput interface.

Specified by:
readUnsignedShort in interface DataInput
Returns:
The unsigned short value read as a Java int
Throws:
IOException - If any other error occurs

skipBytes

public final int skipBytes(int n)
            throws IOException
This method attempts to skip and discard the specified number of bytes in the input stream. It may actually skip fewer bytes than requested. This method will not skip any bytes if passed a negative number of bytes to skip.
Specified by:
skipBytes in interface DataInput
Parameters:
n - The requested number of bytes to skip.
Returns:
The requested number of bytes to skip.
Throws:
IOException - If an error occurs.

DataInputStream.java -- FilteredInputStream that implements DataInput Copyright (C) 1998, 1999, 2000, 2001, 2003, 2005, 2008 Free Software Foundation This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.