Package java.io

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Class DataInputStream

public  class  java.io.DataInputStream
    extends  java.io.FilterInputStream  
    implements java.io.DataInput  
{
        // Constructors
    public DataInputStream(InputStream  in);	

        // Methods
    public final int read(byte  b[]);	
    public final int read(byte  b[], int  off, int  len);	
    public final boolean readBoolean();	
    public final byte readByte();	
    public final char readChar();	
    public final double readDouble();	
    public final float readFloat();	
    public final void readFully(byte  b[]);	
    public final void readFully(byte  b[], int  off, int  len);	
    public final int readInt();	
    public final String readLine();	
    public final long readLong();	
    public final short readShort();	
    public final int readUnsignedByte();	
    public final int readUnsignedShort();	
    public final String readUTF();	
    public final static String readUTF(DataInput  in);	
    public final int skipBytes(int  n);	
}

A data input stream lets an application read primitive Java data types from an underlying input stream in a machine-independent way. An application uses a data output stream to write data which can later be read by a data input stream.

Data input streams and data output streams represent Unicode strings in a format that is a slight modification of UTF-8(1) All characters in the range '\u0001' to '\u007F' are represented by a single byte:

0

bits 0-7

The null character '\u0000' and characters in the range '\u0080' to '\u07FF' are represented by a pair of bytes:

1

1

0

bits 6-10

1

0

bits 0-5

Characters in the range '\u0800' to '\uFFFF' are represented by three bytes:

1

1

1

0

bits 12-15

1

0

bits 6-11

1

0

bits 0-5

The two differences between this format and the "standard" UTF-8 format are the following:

• The null byte'\u0000' is encoded in two-byte format rather than one-byte, so that the encoded strings never have embedded nulls.
• Only the one-byte, two-byte, and three-byte formats are used.

Constructors

DataInputStream

public DataInputStream(InputStream  in) 

Creates a new data input stream to read data from the specified input stream.

Parameter	Description
in	the input stream

Methods

read

public final int read(byte  b[]) 

throws IOException 

Reads up to byte.length bytes of data from this data input stream into an array of bytes. This method blocks until some input is available.

The read method of DataInputStream calls the the read method of its underlying input stream with the three arguments b, 0, and b.length, and returns whatever value that method returns.

Return Value:

Returns the total number of bytes read into the buffer, or -1 is there is no more data because the end of the stream has been reached.

Parameter	Description
b	the buffer into which the data is read

Throw:

IOException

If an I/O error occurs.

Overrides:

read in class FilterInputStream .

read

public final int read(byte  b[], int  off, int  len) 

throws IOException 

Reads up to len bytes of data from this data input stream into an array of bytes. This method blocks until some input is available.

The read method of DataInputStream calls the read method of its underlying input stream with the same arguments and returns whatever value that method returns.

Return Value:

Returns the total number of bytes read into the buffer, or -1 is there is no more data because the end of the stream has been reached.

Parameter	Description
b	the buffer into which the data is read
off	the start offset of the data
len	the maximum number of bytes read

Throw:

IOException

If an I/O error occurs.

Overrides:

read in class FilterInputStream .

readBoolean

public final boolean readBoolean() 

throws IOException 

Reads a boolean from this data input stream. This method reads a single byte from the underlying input stream . A value of 0 represents false. Any other value represents true. This method blocks until either the byte is read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the boolean value read.

Throw:

EOFException

If this input stream has reached the end.

Throw:

IOException

If an I/O error occurs.

readByte

public final byte readByte() 

throws IOException 

Reads a signed 8-bit value from this data input stream. This method reads a byte from the underlying input stream . If the byte read is b, where 0 £ b £ 255, then the result is

	(byte)(b) 

This method blocks until either the byte is read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next byte of this input stream as a signed 8-bit byte.

Throws:

EOFException

If this input stream has reached the end.

Throws:

IOException

If an I/O error occurs.

readChar

public final char readChar() 

throws IOException 

Reads a Unicode character from this data input stream. This method reads two bytes from the underlying input stream . If the bytes read, in order, are b1 and b2, where 0 £ b1,b2 £ 255, then the result is equal to

	(char)((b1 << 8) | b2) 

This method blocks until either the two bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next two bytes of this input stream as an Unicode character.

Throws:

EOFException

If this input stream reaches the end before reading two bytes.

Throws:

IOException

If an I/O error occurs.

readDouble

public final double readDouble() 

throws IOException 

Reads a double from this data input stream. This method reads a long value as if by the readLong method and then converts that long to a double using the long-Bits-To-Double method in class Double.

This method blocks until either the eight bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next eight bytes of this input stream, interpreted as a double.

Throw:

EOFException

If this input stream reaches the end before reading eight bytes.

Throw:

IOException

If an I/O error occurs.

readFloat

public final float readFloat() 

throws IOException 

Reads a float from this data input stream. This method reads an int value as if by the readInt method and then converts that int to a float using the intBitsToFloat method in class Float. This method blocks until either the four bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next four bytes of this input stream, interpreted as a float.

Throw:

EOFException

If this input stream reaches the end before reading four bytes.

Throw:

IOException

If an I/O error occurs.

readFully

public final void readFully(byte  b[]) 

throws IOException 

Reads b.length bytes from this data input stream into the byte array. This method reads repeatedly from the underlying stream until all the bytes are read. This method blocks until either all the bytes are read, the end of the stream is detected, or an exception is thrown.

Parameter	Description
b	the buffer into which the data is read

Throw:

EOFException

If this input stream reaches the end before reading all the bytes.

Throw:

IOException

If an I/O error occurs.

readFully

public final void readFully(byte  b[], int  off, int  len) 

throws IOException 

Reads exactly len bytes from this data input stream into the byte array. This method reads repeatedly from the underlying stream until all the bytes are read. This method blocks until either all the bytes are read, the end of the stream is detected, or an exception is thrown.

Parameter	Description
b	the buffer into which the data is read
off	the start offset of the data
len	the number of bytes to read read

Throw:

EOFException

If this input stream reaches the end before reading all the bytes.

Throw:

IOException

If an I/O error occurs.

readInt

public final int readInt() 

throws IOException 

Reads a signed 32-bit integer from this data input stream. This method reads four bytes from the underlying input stream . If the bytes read, in order, are b1, b2, b3, and b4 where 0 £ b1, b2, b3, b4 £ 255, then the result is equal to

	(b1 << 24) | (b2 << 16) + (b3 << 8) + b4 

This method blocks until either the four bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next four bytes of this input stream, interpreted as an int.

Throws:

EOFException

If this input stream reaches the end before reading two bytes.

Throws:

IOException

If an I/O error occurs.

readLine

public final String readLine() 

throws IOException 

Reads the next line of text from this data input stream. This method successively reads bytes from the underlying input stream until it reaches the end of a line of text.

A line of text is terminated by a carriage return character ('\r'), a newline character ('\n'), a carriage return character immediately followed by a newline character, or the end of the input stream. The line-terminating character(s), if any, are included as part of the string returned.

This method blocks until either a newline character is read, a carriage return and the byte following it are read (to see if it is a newline), the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next line of text from this input stream.

Throw:

IOException

If an I/O error occurs.

readLong

public final long readLong() 

throws IOException 

Reads a signed 64-bit integer from this data input stream. This method reads eight bytes from the underlying input stream . If the bytes read, in order, are b1, b2, b3, b4, b5, b6, b7, and b8, where 0 £ b1, b2, b3, b4, b5, b6, b7, b8 £ 255, then the result is equal to

	((long)b1 << 56) +((long)b2 << 48) + 
	     ((long)b3 << 40) + ((long)b4 << 32)+
    	     ((long)b5 << 24) + (b6 << 16) +  
	      		(b7 << 8) + b8 

This method blocks until either the eight bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next eight bytes of this input stream, interpreted as a long.

Throws:

EOFException

If this input stream reaches the end before reading eight bytes.

Throws:

IOException

If an I/O error occurs.

readShort

public final short readShort() 

throws IOException 

Reads a signed 16-bit number from this data input stream. The method reads two bytes from the underlying input stream . If the two bytes read, in order, are b1 and b2, where each of the two values is between 0 and 255, inclusive, then the result is equal to:

(short)((b1 << 8) | b2)

This method blocks until either the two bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next two bytes of this input stream, interpreted as a signed 16-bit number.

Throw:

EOFException

If this input stream reaches the end before reading two bytes.

Throw:

IOException

If an I/O error occurs.

readUnsignedByte

public final int readUnsignedByte() 

throws IOException 

Reads an unsigned 8-bit number from this data input stream. This method reads a byte from this data input stream's underlying input stream and returns that byte This method blocks until either the byte is are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next byte of this input stream, interpreted as an unsigned 8-bit number.

Throw:

EOFException

If this input stream has reached the end.

Throw:

IOException

If an I/O error occurs.

readUnsignedShort

public final int readUnsignedShort() 

throws IOException 

Reads an unsigned 16-bit number from this data input stream. This method reads two bytes from the underlying input stream . If the bytes read, in order, are b1 and b2, where 0 £ b1,b2 £ 255, then the result is equal to

	(b1 << 8) | b2 

This method blocks until either the two bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the next two bytes of this input stream, interprted as an unsigned 16- bit integer.

Throws:

EOFException

If this input stream reaches the end before reading two bytes.

Throws:

IOException

If an I/O error occurs.

readUTF

public final String readUTF() 

throws IOException 

Reads in a string which has been encoded using a modified UTF-8 format from this data input stream. This method calls readUTF(this). See the following method for a more complete description of the format.

This method blocks until either all the bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns a Unicode string.

Throw:

EOFException

If this input stream reaches the end before reading all the bytes.

Throw:

IOException

If an I/O error occurs.

readUTF

public final static String readUTF(DataInput  in) 

throws IOException 

Reads in a string from the specified data input stream. The string has been encoded using a modified using a modified UTF-8 format.

The first two bytes from are read as if by readUnsignedShort . This values gives the number of following bytes that are in the encoded string. (Note: not the length of the resuling string). The following bytes are then interpreted as bytes encoding characters in the UTF-8 format and are converted into characters.

This method blocks until all the bytes are read, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns a Unicode string.

Parameter	Description
in	a data input stream

Throw:

EOFException

If the input stream reaches the end before all the bytes.

Throw:

UTFDataFormatException

If the bytes do not represent a valid UTF-8 encoding of a Unicode string.

Throw:

IOException

If an I/O error occurs.

skipBytes

public final int skipBytes(int  n) 

throws IOException 

Skips exactly n bytes of input in the underlying input stream . This method blocks until either all the bytes are skipped, the end of the stream is detected, or an exception is thrown.

Return Value:

Returns the number of bytes skipped, which is always n.

Parameter	Description
n	the number of bytes to be skipped

Throw:

EOFException

If this input stream reaches the end before skipping all the bytes.

Throw:

IOException

If an I/O error occurs.

Footnotes

(1)X/Open Company Ltd., "File System Safe UCS Transformation Format (FSS_UTF)", X/Open Preliminary Specification, Document Number: P316. This information also appears in ISO/IEC 10646, Annex P.