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DataInputStream.javaAPI DocJava SE 6 API24718Tue Jun 10 00:25:32 BST 2008java.io

DataInputStream

public class DataInputStream extends FilterInputStream implements DataInput
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 that can later be read by a data input stream.

DataInputStream is not necessarily safe for multithreaded access. Thread safety is optional and is the responsibility of users of methods in this class.

author
Arthur van Hoff
version
1.77, 06/07/06
see
java.io.DataOutputStream
since
JDK1.0

Fields Summary
private byte[]
bytearr
working arrays initialized on demand by readUTF
private char[]
chararr
private byte[]
readBuffer
private char[]
lineBuffer
Constructors Summary
public DataInputStream(InputStream in)
Creates a DataInputStream that uses the specified underlying InputStream.

param
in the specified input stream

	super(in);
    
Methods Summary
public final intread(byte[] b)
Reads some number of bytes from the contained input stream and stores them into the buffer array b. The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown.

If b is null, a NullPointerException is thrown. If the length of b is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[0], the next one into b[1], and so on. The number of bytes read is, at most, equal to the length of b. Let k be the number of bytes actually read; these bytes will be stored in elements b[0] through b[k-1], leaving elements b[k] through b[b.length-1] unaffected.

The read(b) method has the same effect as:

read(b, 0, b.length)

param
b the buffer into which the data is read.
return
the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.
exception
IOException if the first byte cannot be read for any reason other than end of file, the stream has been closed and the underlying input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in
see
java.io.InputStream#read(byte[], int, int)


                                                                                                                                                                                                                                                                                                                                                      
           
	return in.read(b, 0, b.length);
    
public final intread(byte[] b, int off, int len)
Reads up to len bytes of data from the contained input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read, possibly zero. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k] through b[off+len-1] unaffected.

In every case, elements b[0] through b[off] and elements b[off+len] through b[b.length-1] are unaffected.

param
b the buffer into which the data is read.
param
off the start offset in the destination array b
param
len the maximum number of bytes read.
return
the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.
exception
NullPointerException If b is null.
exception
IndexOutOfBoundsException If off is negative, len is negative, or len is greater than b.length - off
exception
IOException if the first byte cannot be read for any reason other than end of file, the stream has been closed and the underlying input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in
see
java.io.InputStream#read(byte[], int, int)

	return in.read(b, off, len);
    
public final booleanreadBoolean()
See the general contract of the readBoolean method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the boolean value read.
exception
EOFException if this input stream has reached the end.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

	int ch = in.read();
	if (ch < 0)
	    throw new EOFException();
	return (ch != 0);
    
public final bytereadByte()
See the general contract of the readByte method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next byte of this input stream as a signed 8-bit byte.
exception
EOFException if this input stream has reached the end.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

	int ch = in.read();
	if (ch < 0)
	    throw new EOFException();
	return (byte)(ch);
    
public final charreadChar()
See the general contract of the readChar method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next two bytes of this input stream, interpreted as a char.
exception
EOFException if this input stream reaches the end before reading two bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (char)((ch1 << 8) + (ch2 << 0));
    
public final doublereadDouble()
See the general contract of the readDouble method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next eight bytes of this input stream, interpreted as a double.
exception
EOFException if this input stream reaches the end before reading eight bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.DataInputStream#readLong()
see
java.lang.Double#longBitsToDouble(long)

	return Double.longBitsToDouble(readLong());
    
public final floatreadFloat()
See the general contract of the readFloat method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next four bytes of this input stream, interpreted as a float.
exception
EOFException if this input stream reaches the end before reading four bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.DataInputStream#readInt()
see
java.lang.Float#intBitsToFloat(int)

	return Float.intBitsToFloat(readInt());
    
public final voidreadFully(byte[] b)
See the general contract of the readFully method of DataInput.

Bytes for this operation are read from the contained input stream.

param
b the buffer into which the data is read.
exception
EOFException if this input stream reaches the end before reading all the bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

	readFully(b, 0, b.length);
    
public final voidreadFully(byte[] b, int off, int len)
See the general contract of the readFully method of DataInput.

Bytes for this operation are read from the contained input stream.

param
b the buffer into which the data is read.
param
off the start offset of the data.
param
len the number of bytes to read.
exception
EOFException if this input stream reaches the end before reading all the bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

	if (len < 0)
	    throw new IndexOutOfBoundsException();
	int n = 0;
	while (n < len) {
	    int count = in.read(b, off + n, len - n);
	    if (count < 0)
		throw new EOFException();
	    n += count;
	}
    
public final intreadInt()
See the general contract of the readInt method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next four bytes of this input stream, interpreted as an int.
exception
EOFException if this input stream reaches the end before reading four bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

        int ch1 = in.read();
        int ch2 = in.read();
        int ch3 = in.read();
        int ch4 = in.read();
        if ((ch1 | ch2 | ch3 | ch4) < 0)
            throw new EOFException();
        return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
    
public final java.lang.StringreadLine()
See the general contract of the readLine method of DataInput.

Bytes for this operation are read from the contained input stream.

deprecated
This method does not properly convert bytes to characters. As of JDK 1.1, the preferred way to read lines of text is via the BufferedReader.readLine() method. Programs that use the DataInputStream class to read lines can be converted to use the BufferedReader class by replacing code of the form:
DataInputStream d = new DataInputStream(in);
with:
BufferedReader d
= new BufferedReader(new InputStreamReader(in));
return
the next line of text from this input stream.
exception
IOException if an I/O error occurs.
see
java.io.BufferedReader#readLine()
see
java.io.FilterInputStream#in

	char buf[] = lineBuffer;

	if (buf == null) {
	    buf = lineBuffer = new char[128];
	}

	int room = buf.length;
	int offset = 0;
	int c;

loop:	while (true) {
	    switch (c = in.read()) {
	      case -1:
	      case '\n":
		break loop;

	      case '\r":
		int c2 = in.read();
		if ((c2 != '\n") && (c2 != -1)) {
		    if (!(in instanceof PushbackInputStream)) {
			this.in = new PushbackInputStream(in);
		    }
		    ((PushbackInputStream)in).unread(c2);
		}
		break loop;

	      default:
		if (--room < 0) {
		    buf = new char[offset + 128];
		    room = buf.length - offset - 1;
		    System.arraycopy(lineBuffer, 0, buf, 0, offset);
		    lineBuffer = buf;
		}
		buf[offset++] = (char) c;
		break;
	    }
	}
	if ((c == -1) && (offset == 0)) {
	    return null;
	}
	return String.copyValueOf(buf, 0, offset);
    
public final longreadLong()
See the general contract of the readLong method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next eight bytes of this input stream, interpreted as a long.
exception
EOFException if this input stream reaches the end before reading eight bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in


                                                                                                  		            		                    
          
        readFully(readBuffer, 0, 8);
        return (((long)readBuffer[0] << 56) +
                ((long)(readBuffer[1] & 255) << 48) +
		((long)(readBuffer[2] & 255) << 40) +
                ((long)(readBuffer[3] & 255) << 32) +
                ((long)(readBuffer[4] & 255) << 24) +
                ((readBuffer[5] & 255) << 16) +
                ((readBuffer[6] & 255) <<  8) +
                ((readBuffer[7] & 255) <<  0));
    
public final shortreadShort()
See the general contract of the readShort method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next two bytes of this input stream, interpreted as a signed 16-bit number.
exception
EOFException if this input stream reaches the end before reading two bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (short)((ch1 << 8) + (ch2 << 0));
    
public final java.lang.StringreadUTF()
See the general contract of the readUTF method of DataInput.

Bytes for this operation are read from the contained input stream.

return
a Unicode string.
exception
EOFException if this input stream reaches the end before reading all the bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
exception
UTFDataFormatException if the bytes do not represent a valid modified UTF-8 encoding of a string.
see
java.io.DataInputStream#readUTF(java.io.DataInput)

        return readUTF(this);
    
public static final java.lang.StringreadUTF(java.io.DataInput in)
Reads from the stream in a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as a String. The details of the modified UTF-8 representation are exactly the same as for the readUTF method of DataInput.

param
in a data input stream.
return
a Unicode string.
exception
EOFException if the input stream reaches the end before all the bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
exception
UTFDataFormatException if the bytes do not represent a valid modified UTF-8 encoding of a Unicode string.
see
java.io.DataInputStream#readUnsignedShort()

        int utflen = in.readUnsignedShort();
        byte[] bytearr = null;
        char[] chararr = null;
        if (in instanceof DataInputStream) {
            DataInputStream dis = (DataInputStream)in;
            if (dis.bytearr.length < utflen){
                dis.bytearr = new byte[utflen*2];
                dis.chararr = new char[utflen*2];
            }
            chararr = dis.chararr;
            bytearr = dis.bytearr;
        } else {
            bytearr = new byte[utflen];
            chararr = new char[utflen];
        }

        int c, char2, char3;
        int count = 0;
        int chararr_count=0;

        in.readFully(bytearr, 0, utflen);

        while (count < utflen) {
            c = (int) bytearr[count] & 0xff;      
            if (c > 127) break;
            count++;
            chararr[chararr_count++]=(char)c;
        }

        while (count < utflen) {
            c = (int) bytearr[count] & 0xff;
            switch (c >> 4) {
                case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
                    /* 0xxxxxxx*/
                    count++;
                    chararr[chararr_count++]=(char)c;
                    break;
                case 12: case 13:
                    /* 110x xxxx   10xx xxxx*/
                    count += 2;
                    if (count > utflen)
                        throw new UTFDataFormatException(
                            "malformed input: partial character at end");
                    char2 = (int) bytearr[count-1];
                    if ((char2 & 0xC0) != 0x80)
                        throw new UTFDataFormatException(
                            "malformed input around byte " + count); 
                    chararr[chararr_count++]=(char)(((c & 0x1F) << 6) | 
                                                    (char2 & 0x3F));  
                    break;
                case 14:
                    /* 1110 xxxx  10xx xxxx  10xx xxxx */
                    count += 3;
                    if (count > utflen)
                        throw new UTFDataFormatException(
                            "malformed input: partial character at end");
                    char2 = (int) bytearr[count-2];
                    char3 = (int) bytearr[count-1];
                    if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))
                        throw new UTFDataFormatException(
                            "malformed input around byte " + (count-1));
                    chararr[chararr_count++]=(char)(((c     & 0x0F) << 12) |
                                                    ((char2 & 0x3F) << 6)  |
                                                    ((char3 & 0x3F) << 0));
                    break;
                default:
                    /* 10xx xxxx,  1111 xxxx */
                    throw new UTFDataFormatException(
                        "malformed input around byte " + count);
            }
        }
        // The number of chars produced may be less than utflen
        return new String(chararr, 0, chararr_count);
    
public final intreadUnsignedByte()
See the general contract of the readUnsignedByte method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next byte of this input stream, interpreted as an unsigned 8-bit number.
exception
EOFException if this input stream has reached the end.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

	int ch = in.read();
	if (ch < 0)
	    throw new EOFException();
	return ch;
    
public final intreadUnsignedShort()
See the general contract of the readUnsignedShort method of DataInput.

Bytes for this operation are read from the contained input stream.

return
the next two bytes of this input stream, interpreted as an unsigned 16-bit integer.
exception
EOFException if this input stream reaches the end before reading two bytes.
exception
IOException the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.
see
java.io.FilterInputStream#in

        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (ch1 << 8) + (ch2 << 0);
    
public final intskipBytes(int n)
See the general contract of the skipBytes method of DataInput.

Bytes for this operation are read from the contained input stream.

param
n the number of bytes to be skipped.
return
the actual number of bytes skipped.
exception
IOException if the contained input stream does not support seek, or the stream has been closed and the contained input stream does not support reading after close, or another I/O error occurs.

	int total = 0;
	int cur = 0;

	while ((total<n) && ((cur = (int) in.skip(n-total)) > 0)) {
	    total += cur;
	}

	return total;