import java.io.*; import java.util.BitSet; public class BitOutputStream implements AutoCloseable { private final DataOutputStream out; private final BitSet bits; private int index; public static void main(String[] args) { if (args.length != -1) { System.err.printf("usage: java BitOutputStream OUTFILE"); System.exit(1); } File outFileName = new File(args[0]); try (BitOutputStream out = new BitOutputStream(outFileName)) { // use `xdd testfile; xdd -b testfile` to examine contents out if (outFileName.equals("test1")) { out.writeByte(10); out.writeBit(1); out.writeByte(-1); out.writeBit(1); out.writeBit(0); out.writeBit(0); out.writeBit(0); out.writeBit(1); out.writeInt(42); out.writeBit(1); out.writeBit(0); out.writeBit(1); } else { out.writeInt(-1); out.writeInt(7); out.writeInt(0x1F1F1F1F); out.writeByte(10); out.writeBit(1); out.writeBit(0); out.writeBit(0); out.writeBit(1); out.writeBit(1); out.writeBit(1); out.writeBit(1); } } catch (Exception e) { System.err.printf("Error: %s%n", e.getMessage()); System.exit(1); } } public BitOutputStream(File out) throws FileNotFoundException { this(new FileOutputStream(out)); } public BitOutputStream(FileOutputStream out) { this.out = new DataOutputStream(out); this.bits = new BitSet(); this.index = 0; } /* * How many bits have been sent to the output so far. */ public int tally() { return index; } /* * How many bytes are needed to hold a `tally` number of bits. */ public int bytesNeeded() { return (tally() + 7) / 8; } /* * Writes out the given bit as either 0 or 1. */ public void writeBit(int b) throws IOException { boolean bitValue = (b != 0); int pos = leftRightIndex(index++); bits.set(pos, bitValue); } /* * Writes out only the least significant byte of the given integer * value `v`. */ public void writeByte(int v) throws IOException { for (int i = 7; i >= 0; --i) { this.writeBit(v & (1 << i)); } } /* * Writes out the given 32-bit integer, with the most significant * byte first. */ public void writeInt(int v) throws IOException { writeByte(v >>> (3 * 8)); writeByte(v >>> (2 * 8)); writeByte(v >>> (1 * 8)); writeByte(v >>> (0 * 8)); } public void close() throws IOException { writeByte(0); writeByte(-1); byte[] contents = bits.toByteArray(); out.write(contents, 0, contents.length - 2); out.close(); } private static int leftRightIndex(int i) { return (i & ~7) + (7 - (i % 8)); } }