JavaStringMemchr.java

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Pointer;
import sun.misc.Unsafe;

import java.lang.reflect.Field;

public class Program {

    private static final Unsafe UNSAFE;

    static {
        Unsafe it = null;
        try {
            Field field = Unsafe.class.getDeclaredField("theUnsafe");
            field.setAccessible(true);
            it = (Unsafe) field.get(null);
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            UNSAFE = it;
        }
    }

    public static void main(String[] args) throws Exception {

        byte[] data = {'h', 'e', 'l', 'l', 'o'};

        Pointer ptr = new Pointer(toAddress(data) + Unsafe.ARRAY_BYTE_BASE_OFFSET);

        Pointer pos = CLibrary.INSTANCE.memchr(ptr, 'e', 5);

        System.out.println((char) pos.getByte(0));
    }

    static long toAddress(Object obj) {
        Object[] array = new Object[] {obj};
        long baseOffset = UNSAFE.arrayBaseOffset(Object[].class);
        long address = UNSAFE.getLong(array, baseOffset);
        return address << 3;  // compressed Oops
    }
}

interface CLibrary extends Library {
    CLibrary INSTANCE = (CLibrary) Native.loadLibrary ("c", CLibrary.class);

    Pointer memchr(Pointer s, int c, long n);
}