DataInput (Java Card API, Connected Edition)
Date: 2009-12-11

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## java.io
Interface DataInput

All Known Subinterfaces:
  Datagram

All Known Implementing Classes:
  DataInputStream

    public interface DataInput

The `DataInput` interface provides for reading bytes from a binary stream and reconstructing from them data in any of the Java primitive types. There is also a facility for reconstructing a `String` from data in Java modified UTF-8 format.

It is generally true of all the reading routines in this interface that if end of file is reached before the desired number of bytes has been read, an `EOFException` (which is a kind of `IOException`) is thrown. If any byte cannot be read for any reason other than end of file, an `IOException` other than `EOFException` is thrown. In particular, an `IOException` may be thrown if the input stream has been closed.

Since:
  JDK1.0, CLDC 1.0, Java Card 3.0
See Also:
  `DataInputStream`, `DataOutput`

Method Summary
`boolean` | `readBoolean()` Reads one input byte and returns `true` if that byte is nonzero, `false` if that byte is zero.
`byte` | `readByte()` Reads and returns one input byte.
`char` | `readChar()` Reads an input `char` and returns the `char` value.
`void` | `readFully(byte[] b)` Reads some bytes from an input stream and stores them into the buffer array `b`.
`void` | `readFully(byte[] b, int off, int len)` Reads `len` bytes from an input stream.
`int` | `readInt()` Reads four input bytes and returns an `int` value.
`long` | `readLong()` Reads eight input bytes and returns a `long` value.
`short` | `readShort()` Reads two input bytes and returns a `short` value.
`int` | `readUnsignedByte()` Reads one input byte, zero-extends it to type `int`, and returns the result, which is therefore in the range `0` through `255`.
`int` | `readUnsignedShort()` Reads two input bytes, zero-extends it to type `int`, and returns an `int` value in the range `0` through `65535`.
`String` | `readUTF()` Reads in a string that has been encoded using a modified UTF-8 format.
`int` | `skipBytes(int n)` Makes an attempt to skip over `n` bytes of data from the input stream, discarding the skipped bytes.

Method Detail

### readFully

    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` - the buffer into which the data is read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readFully

    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` - the buffer into which the data is read.
    `off` - an int specifying the offset into the data.
    `len` - an int specifying the number of bytes to read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### skipBytes

    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` - the number of bytes to be skipped.
  Returns:
    the actual number of bytes skipped.
  Throws:
    `IOException` - if an I/O error occurs.

### readBoolean

    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:
    the `boolean` value read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readByte

    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:
    the 8-bit value read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readUnsignedByte

    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:
    the unsigned 8-bit value read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readShort

    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:
    the 16-bit value read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readUnsignedShort

    int readUnsignedShort()
                          throws IOException

  Reads two input bytes, zero-extends it to type `int`, 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:
    the unsigned 16-bit value read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readChar

    char readChar()
                  throws IOException

  Reads an input `char` and returns the `char` value. A Unicode `char` is made up of two bytes. 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:
    the Unicode `char` read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readInt

    int readInt()
                throws IOException

  Reads four input bytes and returns an `int` value. Let `a` be the first byte read, `b` be the second byte, `c` be the third byte, and `d` be the fourth byte. 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:
    the `int` value read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readLong

    long readLong()
                  throws IOException

  Reads eight input bytes and returns a `long` value. Let `a` be the first byte read, `b` be the second byte, `c` be the third byte, `d` be the fourth byte, `e` be the fifth byte, `f` be the sixth byte, `g` be the seventh byte, and `h` be the eighth byte. 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:
    the `long` value read.
  Throws:
    `EOFException` - if this stream reaches the end before reading all the bytes.
    `IOException` - if an I/O error occurs.

### readUTF

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

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