OpenJDK 1.22 · java.io.DataInput · APIdia, the JavaDoc alternative

Encoding of UTF-8 values
Value	Byte	Bit Values
`\u0001` to `\u007F`	1	0	bits 6-0
`\u0000`, `\u0080` to `\u07FF`	1	1	1	0	bits 10-6
2	1	0	bits 5-0
`\u0800` to `\uFFFF`	1	1	1	1	0	bits 15-12
2	1	0	bits 11-6
3	1	0	bits 5-0

Modifier and Type	Method and Description
public boolean	Returns: the `boolean` value read. readBoolean() Reads one input byte and returns `true` if that byte is nonzero, `false` if that byte is zero.
public byte	Returns: the 8-bit value read. readByte() Reads and returns one input byte.
public char	Returns: the `char` value read. readChar() Reads two input bytes and returns a `char` value.
public double	Returns: the `double` value read. readDouble() Reads eight input bytes and returns a `double` value.
public float	Returns: the `float` value read. readFloat() Reads four input bytes and returns a `float` value.
public void	readFully(byte[] the buffer into which the data is read. b) Reads some bytes from an input stream and stores them into the buffer array `b`.
public void	readFully(byte[] the buffer into which the data is read. b, int an int specifying the offset in the data array `b`. off, int an int specifying the number of bytes to read. len) Reads `len` bytes from an input stream.
public int	Returns: the `int` value read. readInt() Reads four input bytes and returns an `int` value.
public String	Returns: the next line of text from the input stream, or `null` if the end of file is encountered before a byte can be read. readLine() Reads the next line of text from the input stream.
public long	Returns: the `long` value read. readLong() Reads eight input bytes and returns a `long` value.
public short	Returns: the 16-bit value read. readShort() Reads two input bytes and returns a `short` value.
public int	Returns: the unsigned 8-bit value read. readUnsignedByte() Reads one input byte, zero-extends it to type `int`, and returns the result, which is therefore in the range `0` through `255`.
public int	Returns: the unsigned 16-bit value read. readUnsignedShort() Reads two input bytes and returns an `int` value in the range `0` through `65535`.
public String	Returns: a Unicode string. readUTF() Reads in a string that has been encoded using a modified UTF-8 format.
public int	Returns: the number of bytes actually skipped. skipBytes(int the number of bytes to be skipped. n) Makes an attempt to skip over `n` bytes of data from the input stream, discarding the skipped bytes.

Method Detail

readBoolean back to summary

readBoolean	back to summary
public boolean readBoolean() throws IOException Reads one input byte and returns `true` if that byte is nonzero, `false` if that byte is zero. This method is suitable for reading the byte written by the `writeBoolean` method of interface `DataOutput`. Returns:boolean the `boolean` value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public boolean readBoolean() throws IOException

Reads one input byte and returns true if that byte is nonzero, false if that byte is zero. This method is suitable for reading the byte written by the writeBoolean method of interface DataOutput.

Returns:boolean

the boolean value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readByte back to summary

readByte	back to summary
public byte readByte() throws IOException Reads and returns one input byte. The byte is treated as a signed value in the range `-128` through `127`, inclusive. This method is suitable for reading the byte written by the `writeByte` method of interface `DataOutput`. Returns:byte the 8-bit value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public byte readByte() throws IOException

Reads and returns one input byte. The byte is treated as a signed value in the range -128 through 127, inclusive. This method is suitable for reading the byte written by the writeByte method of interface DataOutput.

Returns:byte

the 8-bit value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readChar back to summary

readChar	back to summary
public char readChar() throws IOException Reads two input bytes and returns a `char` value. Let `a` be the first byte read and `b` be the second byte. The value returned is: `(char)((a << 8) \| (b & 0xff))` This method is suitable for reading bytes written by the `writeChar` method of interface `DataOutput`. Returns:char the `char` value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public char readChar() throws IOException

Reads two input bytes and returns a char value. Let a be the first byte read and b be the second byte. The value returned is:

(char)((a << 8) | (b & 0xff))

This method is suitable for reading bytes written by the writeChar method of interface DataOutput.

Returns:char

the char value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readDouble back to summary

readDouble	back to summary
public double readDouble() throws IOException Reads eight input bytes and returns a `double` value. It does this by first constructing a `long` value in exactly the manner of the `readLong` method, then converting this `long` value to a `double` in exactly the manner of the method `Double.longBitsToDouble`. This method is suitable for reading bytes written by the `writeDouble` method of interface `DataOutput`. Returns:double the `double` value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public double readDouble() throws IOException

Reads eight input bytes and returns a double value. It does this by first constructing a long value in exactly the manner of the readLong method, then converting this long value to a double in exactly the manner of the method Double.longBitsToDouble. This method is suitable for reading bytes written by the writeDouble method of interface DataOutput.

Returns:double

the double value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readFloat back to summary

readFloat	back to summary
public float readFloat() throws IOException Reads four input bytes and returns a `float` value. It does this by first constructing an `int` value in exactly the manner of the `readInt` method, then converting this `int` value to a `float` in exactly the manner of the method `Float.intBitsToFloat`. This method is suitable for reading bytes written by the `writeFloat` method of interface `DataOutput`. Returns:float the `float` value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public float readFloat() throws IOException

Reads four input bytes and returns a float value. It does this by first constructing an int value in exactly the manner of the readInt method, then converting this int value to a float in exactly the manner of the method Float.intBitsToFloat. This method is suitable for reading bytes written by the writeFloat method of interface DataOutput.

Returns:float

the float value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readFully back to summary

readFully	back to summary
public void readFully(byte[] b) throws IOException Reads some bytes from an input stream and stores them into the buffer array `b`. The number of bytes read is equal to the length of `b`. This method blocks until one of the following conditions occurs: `b.length` bytes of input data are available, in which case a normal return is made. End of file is detected, in which case an `EOFException` is thrown. An I/O error occurs, in which case an `IOException` other than `EOFException` is thrown. If `b` is `null`, a `NullPointerException` is thrown. If `b.length` is zero, then no bytes are read. Otherwise, the first byte read is stored into element `b[0]`, the next one into `b[1]`, and so on. If an exception is thrown from this method, then it may be that some but not all bytes of `b` have been updated with data from the input stream. Parameters b:byte[] the buffer into which the data is read. Exceptions IOException: if an I/O error occurs. NullPointerException: if `b` is `null`. EOFException: if this stream reaches the end before reading all the bytes.

public void readFully(byte[] b) throws IOException

Reads some bytes from an input stream and stores them into the buffer array b. The number of bytes read is equal to the length of b.

This method blocks until one of the following conditions occurs:

b.length bytes of input data are available, in which case a normal return is made.
End of file is detected, in which case an EOFException is thrown.
An I/O error occurs, in which case an IOException other than EOFException is thrown.

If b is null, a NullPointerException is thrown. If b.length is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[0], the next one into b[1], and so on. If an exception is thrown from this method, then it may be that some but not all bytes of b have been updated with data from the input stream.

Parameters

b:byte[]: the buffer into which the data is read.

Exceptions

IOException:: if an I/O error occurs.
NullPointerException:: if b is null.
EOFException:: if this stream reaches the end before reading all the bytes.

readFully back to summary

readFully	back to summary
public void readFully(byte[] b, int off, int len) throws IOException Reads `len` bytes from an input stream. This method blocks until one of the following conditions occurs: `len` bytes of input data are available, in which case a normal return is made. End of file is detected, in which case an `EOFException` is thrown. An I/O error occurs, in which case an `IOException` other than `EOFException` is thrown. If `b` is `null`, a `NullPointerException` is thrown. If `off` is negative, or `len` is negative, or `off+len` is greater than the length of the array `b`, then an `IndexOutOfBoundsException` is thrown. If `len` is zero, then no bytes are read. Otherwise, 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`. Parameters b:byte[] the buffer into which the data is read. off:int an int specifying the offset in the data array `b`. len:int an int specifying the number of bytes to read. Exceptions IOException: if an I/O error occurs. NullPointerException: if `b` is `null`. IndexOutOfBoundsException: if `off` is negative, `len` is negative, or `len` is greater than `b.length - off`. EOFException: if this stream reaches the end before reading all the bytes.

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

Reads len bytes from an input stream.

This method blocks until one of the following conditions occurs:

len bytes of input data are available, in which case a normal return is made.
End of file is detected, in which case an EOFException is thrown.
An I/O error occurs, in which case an IOException other than EOFException is thrown.

If b is null, a NullPointerException is thrown. If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown. If len is zero, then no bytes are read. Otherwise, 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.

Parameters

b:byte[]: the buffer into which the data is read.
off:int: an int specifying the offset in the data array b.
len:int: an int specifying the number of bytes to read.

Exceptions

IOException:: if an I/O error occurs.
NullPointerException:: if b is null.
IndexOutOfBoundsException:: if off is negative, len is negative, or len is greater than b.length - off.
EOFException:: if this stream reaches the end before reading all the bytes.

readInt back to summary

readInt	back to summary
public int readInt() throws IOException Reads four input bytes and returns an `int` value. Let `a-d` be the first through fourth bytes read. The value returned is: `(((a & 0xff) << 24) \| ((b & 0xff) << 16) \| ((c & 0xff) << 8) \| (d & 0xff))` This method is suitable for reading bytes written by the `writeInt` method of interface `DataOutput`. Returns:int the `int` value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public int readInt() throws IOException

Reads four input bytes and returns an int value. Let a-d be the first through fourth bytes read. The value returned is:

(((a & 0xff) << 24) | ((b & 0xff) << 16) |
 ((c & 0xff) <<  8) | (d & 0xff))

This method is suitable for reading bytes written by the writeInt method of interface DataOutput.

Returns:int

the int value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readLine back to summary

readLine	back to summary
public String readLine() throws IOException Reads the next line of text from the input stream. It reads successive bytes, converting each byte separately into a character, until it encounters a line terminator or end of file; the characters read are then returned as a `String`. Note that because this method processes bytes, it does not support input of the full Unicode character set. If end of file is encountered before even one byte can be read, then `null` is returned. Otherwise, each byte that is read is converted to type `char` by zero-extension. If the character `'\n'` is encountered, it is discarded and reading ceases. If the character `'\r'` is encountered, it is discarded and, if the following byte converts to the character `'\n'`, then that is discarded also; reading then ceases. If end of file is encountered before either of the characters `'\n'` and `'\r'` is encountered, reading ceases. Once reading has ceased, a `String` is returned that contains all the characters read and not discarded, taken in order. Note that every character in this string will have a value less than `\u0100`, that is, `(char)256`. Returns:String the next line of text from the input stream, or `null` if the end of file is encountered before a byte can be read. Exceptions IOException: if an I/O error occurs.

public String readLine() throws IOException

Reads the next line of text from the input stream. It reads successive bytes, converting each byte separately into a character, until it encounters a line terminator or end of file; the characters read are then returned as a String. Note that because this method processes bytes, it does not support input of the full Unicode character set.

If end of file is encountered before even one byte can be read, then null is returned. Otherwise, each byte that is read is converted to type char by zero-extension. If the character '\n' is encountered, it is discarded and reading ceases. If the character '\r' is encountered, it is discarded and, if the following byte converts to the character '\n', then that is discarded also; reading then ceases. If end of file is encountered before either of the characters '\n' and '\r' is encountered, reading ceases. Once reading has ceased, a String is returned that contains all the characters read and not discarded, taken in order. Note that every character in this string will have a value less than \u0100, that is, (char)256.

Returns:String

the next line of text from the input stream, or null if the end of file is encountered before a byte can be read.

Exceptions

IOException:: if an I/O error occurs.

readLong back to summary

readLong	back to summary
public long readLong() throws IOException Reads eight input bytes and returns a `long` value. Let `a-h` be the first through eighth bytes read. The value returned is: `(((long)(a & 0xff) << 56) \| ((long)(b & 0xff) << 48) \| ((long)(c & 0xff) << 40) \| ((long)(d & 0xff) << 32) \| ((long)(e & 0xff) << 24) \| ((long)(f & 0xff) << 16) \| ((long)(g & 0xff) << 8) \| ((long)(h & 0xff)))` This method is suitable for reading bytes written by the `writeLong` method of interface `DataOutput`. Returns:long the `long` value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public long readLong() throws IOException

Reads eight input bytes and returns a long value. Let a-h be the first through eighth bytes read. The value returned is:

(((long)(a & 0xff) << 56) |
 ((long)(b & 0xff) << 48) |
 ((long)(c & 0xff) << 40) |
 ((long)(d & 0xff) << 32) |
 ((long)(e & 0xff) << 24) |
 ((long)(f & 0xff) << 16) |
 ((long)(g & 0xff) <<  8) |
 ((long)(h & 0xff)))

This method is suitable for reading bytes written by the writeLong method of interface DataOutput.

Returns:long

the long value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readShort back to summary

readShort	back to summary
public short readShort() throws IOException Reads two input bytes and returns a `short` value. Let `a` be the first byte read and `b` be the second byte. The value returned is: `(short)((a << 8) \| (b & 0xff))` This method is suitable for reading the bytes written by the `writeShort` method of interface `DataOutput`. Returns:short the 16-bit value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public short readShort() throws IOException

Reads two input bytes and returns a short value. Let a be the first byte read and b be the second byte. The value returned is:

(short)((a << 8) | (b & 0xff))

This method is suitable for reading the bytes written by the writeShort method of interface DataOutput.

Returns:short

the 16-bit value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readUnsignedByte back to summary

readUnsignedByte	back to summary
public int readUnsignedByte() throws IOException Reads one input byte, zero-extends it to type `int`, and returns the result, which is therefore in the range `0` through `255`. This method is suitable for reading the byte written by the `writeByte` method of interface `DataOutput` if the argument to `writeByte` was intended to be a value in the range `0` through `255`. Returns:int the unsigned 8-bit value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public int readUnsignedByte() throws IOException

Reads one input byte, zero-extends it to type int, and returns the result, which is therefore in the range 0 through 255. This method is suitable for reading the byte written by the writeByte method of interface DataOutput if the argument to writeByte was intended to be a value in the range 0 through 255.

Returns:int

the unsigned 8-bit value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readUnsignedShort back to summary

readUnsignedShort	back to summary
public int readUnsignedShort() throws IOException Reads two input bytes and returns an `int` value in the range `0` through `65535`. Let `a` be the first byte read and `b` be the second byte. The value returned is: `(((a & 0xff) << 8) \| (b & 0xff))` This method is suitable for reading the bytes written by the `writeShort` method of interface `DataOutput` if the argument to `writeShort` was intended to be a value in the range `0` through `65535`. Returns:int the unsigned 16-bit value read. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes.

public int readUnsignedShort() throws IOException

Reads two input bytes and returns an int value in the range 0 through 65535. Let a be the first byte read and b be the second byte. The value returned is:

(((a & 0xff) << 8) | (b & 0xff))

This method is suitable for reading the bytes written by the writeShort method of interface DataOutput if the argument to writeShort was intended to be a value in the range 0 through 65535.

Returns:int

the unsigned 16-bit value read.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.

readUTF back to summary

readUTF	back to summary
public String readUTF() throws IOException Reads in a string that has been encoded using a modified UTF-8 format. The general contract of `readUTF` is that it reads a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as a `String`. First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the `readUnsignedShort` method . This integer value is called the UTF length and specifies the number of additional bytes to be read. These bytes are then converted to characters by considering them in groups. The length of each group is computed from the value of the first byte of the group. The byte following a group, if any, is the first byte of the next group. If the first byte of a group matches the bit pattern `0xxxxxxx` (where `x` means "may be `0` or `1`"), then the group consists of just that byte. The byte is zero-extended to form a character. If the first byte of a group matches the bit pattern `110xxxxx`, then the group consists of that byte `a` and a second byte `b`. If there is no byte `b` (because byte `a` was the last of the bytes to be read), or if byte `b` does not match the bit pattern `10xxxxxx`, then a `UTFDataFormatException` is thrown. Otherwise, the group is converted to the character: `(char)(((a & 0x1F) << 6) \| (b & 0x3F))` If the first byte of a group matches the bit pattern `1110xxxx`, then the group consists of that byte `a` and two more bytes `b` and `c`. If there is no byte `c` (because byte `a` was one of the last two of the bytes to be read), or either byte `b` or byte `c` does not match the bit pattern `10xxxxxx`, then a `UTFDataFormatException` is thrown. Otherwise, the group is converted to the character: `(char)(((a & 0x0F) << 12) \| ((b & 0x3F) << 6) \| (c & 0x3F))` If the first byte of a group matches the pattern `1111xxxx` or the pattern `10xxxxxx`, then a `UTFDataFormatException` is thrown. If end of file is encountered at any time during this entire process, then an `EOFException` is thrown. After every group has been converted to a character by this process, the characters are gathered, in the same order in which their corresponding groups were read from the input stream, to form a `String`, which is returned. The `writeUTF` method of interface `DataOutput` may be used to write data that is suitable for reading by this method. Returns:String a Unicode string. Exceptions IOException: if an I/O error occurs. EOFException: if this stream reaches the end before reading all the bytes. UTFDataFormatException: if the bytes do not represent a valid modified UTF-8 encoding of a string.

public String readUTF() throws IOException

Reads in a string that has been encoded using a modified UTF-8 format. The general contract of readUTF is that it reads a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as a String.

First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the readUnsignedShort method . This integer value is called the UTF length and specifies the number of additional bytes to be read. These bytes are then converted to characters by considering them in groups. The length of each group is computed from the value of the first byte of the group. The byte following a group, if any, is the first byte of the next group.

If the first byte of a group matches the bit pattern 0xxxxxxx (where x means "may be 0 or 1"), then the group consists of just that byte. The byte is zero-extended to form a character.

If the first byte of a group matches the bit pattern 110xxxxx, then the group consists of that byte a and a second byte b. If there is no byte b (because byte a was the last of the bytes to be read), or if byte b does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:

(char)(((a & 0x1F) << 6) | (b & 0x3F))

If the first byte of a group matches the bit pattern 1110xxxx, then the group consists of that byte a and two more bytes b and c. If there is no byte c (because byte a was one of the last two of the bytes to be read), or either byte b or byte c does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:

(char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))

If the first byte of a group matches the pattern 1111xxxx or the pattern 10xxxxxx, then a UTFDataFormatException is thrown.

If end of file is encountered at any time during this entire process, then an EOFException is thrown.

After every group has been converted to a character by this process, the characters are gathered, in the same order in which their corresponding groups were read from the input stream, to form a String, which is returned.

The writeUTF method of interface DataOutput may be used to write data that is suitable for reading by this method.

Returns:String

a Unicode string.

Exceptions

IOException:: if an I/O error occurs.
EOFException:: if this stream reaches the end before reading all the bytes.
UTFDataFormatException:: if the bytes do not represent a valid modified UTF-8 encoding of a string.

skipBytes back to summary

skipBytes	back to summary
public int skipBytes(int n) throws IOException Makes an attempt to skip over `n` bytes of data from the input stream, discarding the skipped bytes. However, it may skip over some smaller number of bytes, possibly zero. This may result from any of a number of conditions; reaching end of file before `n` bytes have been skipped is only one possibility. This method never throws an `EOFException`. The actual number of bytes skipped is returned. Parameters n:int the number of bytes to be skipped. Returns:int the number of bytes actually skipped. Exceptions IOException: if an I/O error occurs.

public int skipBytes(int n) throws IOException

Makes an attempt to skip over n bytes of data from the input stream, discarding the skipped bytes. However, it may skip over some smaller number of bytes, possibly zero. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. This method never throws an EOFException. The actual number of bytes skipped is returned.

Parameters

n:int: the number of bytes to be skipped.

Returns:int

the number of bytes actually skipped.

Exceptions

IOException:: if an I/O error occurs.

public Interface DataInput

Modified UTF-8

Method Summary

Method Detail