Package org.apache.commons.compress.harmony.pack200

Class Codec

java.lang.Object
org.apache.commons.compress.harmony.pack200.Codec
Direct Known Subclasses:
BHSDCodec, PopulationCodec, RunCodec
public abstract class Codec extends Object
A Codec allows a sequence of bytes to be decoded into integer values (or vice versa).

There are a number of standard Codecs (UDELTA5, UNSIGNED5, BYTE1, CHAR3) that are used in the implementation of many bands; but there are a variety of other ones, and indeed the specification assumes that other combinations of values can result in more specific and efficient formats. There are also a sequence of canonical encodings defined by the Pack200 specification, which allow a Codec to be referred to by canonical number. CodecEncoding.getCodec(int, InputStream, Codec))

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final BHSDCodec
    BCI5
    BCI5 = (5,4): Used for storing branching information in bytecode.
    static final BHSDCodec
    BRANCH5
    BRANCH5 = (5,4,2): Used for storing branching information in bytecode.
    static final BHSDCodec
    BYTE1
    BYTE1 = (1,256): Used for storing plain bytes.
    static final BHSDCodec
    CHAR3
    CHAR3 = (3,128): Used for storing text (UTF-8) strings.
    static final BHSDCodec
    DELTA5
    DELTA5 = (5,64,1,1): Used for the majority of numerical codings where there is a correlated sequence of signed values.
    int
    lastBandLength
     
    static final BHSDCodec
    MDELTA5
    MDELTA5 = (5,64,2,1): Used for the majority of numerical codings where there is a correlated sequence of signed values, but where most of them are expected to be non-negative.
    static final BHSDCodec
    SIGNED5
    SIGNED5 = (5,64,1): Used for small signed values.
    static final BHSDCodec
    UDELTA5
    UDELTA5 = (5,64,0,1): Used for the majority of numerical codings where there is a correlated sequence of unsigned values.
    static final BHSDCodec
    UNSIGNED5
    UNSIGNED5 = (5,64): Used for small unsigned values.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Codec()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    abstract int
    decode(InputStream in)
    Decodes a sequence of bytes from the given input stream, returning the value as a long.
    abstract int
    decode(InputStream in, long last)
    Decodes a sequence of bytes from the given input stream, returning the value as a long.
    int[]
    decodeInts(int n, InputStream in)
    Decodes a sequence of n values from in.
    int[]
    decodeInts(int n, InputStream in, int firstValue)
    Decodes a sequence of n values from in.
    abstract byte[]
    encode(int value)
    Encodes a single value into a sequence of bytes.
    byte[]
    encode(int[] ints)
    Encodes a sequence of integers into a byte array
    abstract byte[]
    encode(int value, int last)
    Encodes a single value into a sequence of bytes.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • BCI5

      public static final BHSDCodec BCI5
      BCI5 = (5,4): Used for storing branching information in bytecode.

    • BRANCH5

      public static final BHSDCodec BRANCH5
      BRANCH5 = (5,4,2): Used for storing branching information in bytecode.

    • BYTE1

      public static final BHSDCodec BYTE1
      BYTE1 = (1,256): Used for storing plain bytes.

    • CHAR3

      public static final BHSDCodec CHAR3
      CHAR3 = (3,128): Used for storing text (UTF-8) strings. This isn't quite the same as UTF-8, but has similar properties; ASCII characters < 127 are stored in a single byte.

    • DELTA5

      public static final BHSDCodec DELTA5
      DELTA5 = (5,64,1,1): Used for the majority of numerical codings where there is a correlated sequence of signed values.

    • MDELTA5

      public static final BHSDCodec MDELTA5
      MDELTA5 = (5,64,2,1): Used for the majority of numerical codings where there is a correlated sequence of signed values, but where most of them are expected to be non-negative.

    • SIGNED5

      public static final BHSDCodec SIGNED5
      SIGNED5 = (5,64,1): Used for small signed values.

    • UDELTA5

      public static final BHSDCodec UDELTA5
      UDELTA5 = (5,64,0,1): Used for the majority of numerical codings where there is a correlated sequence of unsigned values.

    • UNSIGNED5

      public static final BHSDCodec UNSIGNED5
      UNSIGNED5 = (5,64): Used for small unsigned values.

    • lastBandLength

      public int lastBandLength

  • Constructor Details

  • Method Details

    • decode

      public abstract int decode(InputStream in) throws IOException, Pack200Exception
      Decodes a sequence of bytes from the given input stream, returning the value as a long. Note that this method can only be applied for non-delta encodings.
      Parameters:
      in - the input stream to read from
      Returns:
      the value as a long
      Throws:
      IOException - if there is a problem reading from the underlying input stream
      Pack200Exception - if the encoding is a delta encoding

    • decode

      public abstract int decode(InputStream in, long last) throws IOException, Pack200Exception
      Decodes a sequence of bytes from the given input stream, returning the value as a long. If this encoding is a delta encoding (d=1) then the previous value must be passed in as a parameter. If it is a non-delta encoding, then it does not matter what value is passed in, so it makes sense for the value to be passed in by default using code similar to: 
       long last = 0;
 while (condition) {
     last = codec.decode(in, last);
     // do something with last
 }
      Parameters:
      in - the input stream to read from
      last - the previous value read, which must be supplied if the codec is a delta encoding
      Returns:
      the value as a long
      Throws:
      IOException - if there is a problem reading from the underlying input stream
      Pack200Exception - if there is a problem decoding the value or that the value is invalid

    • decodeInts

      public int[] decodeInts(int n, InputStream in) throws IOException, Pack200Exception
      Decodes a sequence of n values from in. This should probably be used in most cases, since some codecs (such as PopulationCodec) only work when the number of values to be read is known.
      Parameters:
      n - the number of values to decode
      in - the input stream to read from
      Returns:
      an array of int values corresponding to values decoded
      Throws:
      IOException - if there is a problem reading from the underlying input stream
      Pack200Exception - if there is a problem decoding the value or that the value is invalid

    • decodeInts

      public int[] decodeInts(int n, InputStream in, int firstValue) throws IOException, Pack200Exception
      Decodes a sequence of n values from in.
      Parameters:
      n - the number of values to decode
      in - the input stream to read from
      firstValue - the first value in the band if it has already been read
      Returns:
      an array of int values corresponding to values decoded, with firstValue as the first value in the array.
      Throws:
      IOException - if there is a problem reading from the underlying input stream
      Pack200Exception - if there is a problem decoding the value or that the value is invalid

    • encode

      public abstract byte[] encode(int value) throws Pack200Exception
      Encodes a single value into a sequence of bytes. Note that this method can only be used for non-delta encodings.
      Parameters:
      value - the value to encode
      Returns:
      the encoded bytes
      Throws:
      Pack200Exception - TODO

    • encode

      public abstract byte[] encode(int value, int last) throws Pack200Exception
      Encodes a single value into a sequence of bytes.
      Parameters:
      value - the value to encode
      last - the previous value encoded (for delta encodings)
      Returns:
      the encoded bytes
      Throws:
      Pack200Exception - TODO

    • encode

      public byte[] encode(int[] ints) throws Pack200Exception
      Encodes a sequence of integers into a byte array
      Parameters:
      ints - the values to encode
      Returns:
      byte[] encoded bytes
      Throws:
      Pack200Exception - if there is a problem encoding any of the values