Java by API/java.util.zip/Checksum

Checksum: getValue()

       
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.CRC32;
import java.util.zip.Checksum;
public class Main {
  public static void main(String[] args) throws IOException {
    FileInputStream fin = new FileInputStream(args[0]);
    System.out.println(args[0] + ":\t" + getCRC32(fin));
    fin.close();
  }
  public static long getCRC32(InputStream in) throws IOException {
    Checksum cs = new CRC32();
    for (int b = in.read(); b != -1; b = in.read()) {
      cs.update(b);
    }
    return cs.getValue();
  }
}

Checksum: reset()

 
import java.util.zip.CRC32;
import java.util.zip.Checksum;
public class Main {
  public static void main(String[] argv) throws Exception {
    byte[] bytes = "some data".getBytes();
    // Compute Adler-32 checksum
    Checksum checksumEngine = new CRC32();
    checksumEngine.update(bytes, 0, bytes.length);
    long checksum = checksumEngine.getValue();
    checksumEngine.reset();
  }
}

Checksum: update(int b)

       
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.CRC32;
import java.util.zip.Checksum;
public class Main {
  public static void main(String[] args) throws IOException {
    FileInputStream fin = new FileInputStream(args[0]);
    System.out.println(args[0] + ":\t" + getCRC32(fin));
    fin.close();
  }
  public static long getCRC32(InputStream in) throws IOException {
    Checksum cs = new CRC32();
    for (int b = in.read(); b != -1; b = in.read()) {
      cs.update(b);
    }
    return cs.getValue();
  }
}

implements Checksum

 
import java.util.zip.Checksum;
public class ParityChecksum implements Checksum {
  long checksum = 0;
  public void update(int b) {
    int numOneBits = 0;
    for (int i = 1; i < 256; i *= 2) {
      if ((b & i) != 0)
        numOneBits++;
    }
    checksum = (checksum + numOneBits) % 2;
  }
  public void update(byte data[], int offset, int length) {
    for (int i = offset; i < offset + length; i++) {
      this.update(data[i]);
    }
  }
  public long getValue() {
    return checksum;
  }
  public void reset() {
    checksum = 0;
  }
}