Class Codec
- java.lang.Object
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- org.apache.commons.compress.harmony.pack200.Codec
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- Direct Known Subclasses:
BHSDCodec
,PopulationCodec
,RunCodec
public abstract class Codec extends java.lang.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)
)
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Field Summary
Fields Modifier and Type Field Description static BHSDCodec
BCI5
BCI5 = (5,4): Used for storing branching information in bytecode.static BHSDCodec
BRANCH5
BRANCH5 = (5,4,2): Used for storing branching information in bytecode.static BHSDCodec
BYTE1
BYTE1 = (1,256): Used for storing plain bytes.static BHSDCodec
CHAR3
CHAR3 = (3,128): Used for storing text (UTF-8) strings.static 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 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 BHSDCodec
SIGNED5
SIGNED5 = (5,64,1): Used for small signed values.static BHSDCodec
UDELTA5
UDELTA5 = (5,64,0,1): Used for the majority of numerical codings where there is a correlated sequence of unsigned values.static BHSDCodec
UNSIGNED5
UNSIGNED5 = (5,64): Used for small unsigned values.
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Constructor Summary
Constructors Constructor Description Codec()
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract int
decode(java.io.InputStream in)
Decode a sequence of bytes from the given input stream, returning the value as a long.abstract int
decode(java.io.InputStream in, long last)
Decode a sequence of bytes from the given input stream, returning the value as a long.int[]
decodeInts(int n, java.io.InputStream in)
Decodes a sequence ofn
values fromin
.int[]
decodeInts(int n, java.io.InputStream in, int firstValue)
Decodes a sequence ofn
values fromin
.abstract byte[]
encode(int value)
Encode a single value into a sequence of bytes.byte[]
encode(int[] ints)
Encode a sequence of integers into a byte arrayabstract byte[]
encode(int value, int last)
Encode a single value into a sequence of bytes.
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Field Detail
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BCI5
public static final BHSDCodec BCI5
BCI5 = (5,4): Used for storing branching information in bytecode.
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BRANCH5
public static final BHSDCodec BRANCH5
BRANCH5 = (5,4,2): Used for storing branching information in bytecode.
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CHAR3
public static final BHSDCodec CHAR3
CHAR3 = (3,128): Used for storing text (UTF-8) strings. NB This isn't quite the same as UTF-8, but has similar properties; ASCII characters < 127 are stored in a single byte.
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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.
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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.
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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.
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UNSIGNED5
public static final BHSDCodec UNSIGNED5
UNSIGNED5 = (5,64): Used for small unsigned values.
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lastBandLength
public int lastBandLength
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Constructor Detail
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Codec
public Codec()
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Method Detail
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decode
public abstract int decode(java.io.InputStream in) throws java.io.IOException, Pack200Exception
Decode 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:
java.io.IOException
- if there is a problem reading from the underlying input streamPack200Exception
- if the encoding is a delta encoding
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encode
public abstract byte[] encode(int value, int last) throws Pack200Exception
Encode a single value into a sequence of bytes.- Parameters:
value
- the value to encodelast
- the previous value encoded (for delta encodings)- Returns:
- the encoded bytes
- Throws:
Pack200Exception
- TODO
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encode
public abstract byte[] encode(int value) throws Pack200Exception
Encode 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
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decode
public abstract int decode(java.io.InputStream in, long last) throws java.io.IOException, Pack200Exception
Decode 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 fromlast
- the previous value read, which must be supplied if the codec is a delta encoding- Returns:
- the value as a long
- Throws:
java.io.IOException
- if there is a problem reading from the underlying input streamPack200Exception
- if there is a problem decoding the value or that the value is invalid
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decodeInts
public int[] decodeInts(int n, java.io.InputStream in) throws java.io.IOException, Pack200Exception
Decodes a sequence ofn
values fromin
. This should probably be used in most cases, since some codecs (such asPopulationCodec
) only work when the number of values to be read is known.- Parameters:
n
- the number of values to decodein
- the input stream to read from- Returns:
- an array of
int
values corresponding to values decoded - Throws:
java.io.IOException
- if there is a problem reading from the underlying input streamPack200Exception
- if there is a problem decoding the value or that the value is invalid
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decodeInts
public int[] decodeInts(int n, java.io.InputStream in, int firstValue) throws java.io.IOException, Pack200Exception
Decodes a sequence ofn
values fromin
.- Parameters:
n
- the number of values to decodein
- the input stream to read fromfirstValue
- 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:
java.io.IOException
- if there is a problem reading from the underlying input streamPack200Exception
- if there is a problem decoding the value or that the value is invalid
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encode
public byte[] encode(int[] ints) throws Pack200Exception
Encode 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
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