Ring buffer to hold the UART data

RingByteBuffer.java

import org.jetbrains.annotations.NotNull;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Ring buffer (fixed size queue) implementation using a circular array (array
 * with wrap-around).
 */
public class RingByteBuffer implements Iterable<Byte> {
    private final byte[] buffer;     // queue elements
    private int indexTail = 0;       // index of first element of queue
    private int indexHead = 1;       // index of next available slot

    public RingByteBuffer(int capacity) {
        buffer = new byte[capacity + 1];
    }

    public boolean isEmpty() {
        return size() == 0;
    }

    public int size() {
        return (indexHead - indexTail - 1) % buffer.length;
    }

    public void put(byte item) {
        if (indexHead == indexTail) {
            indexTail = (indexTail + 1) % buffer.length;
        }
        buffer[indexHead] = item;
        indexHead = (indexHead + 1) % buffer.length;
    }

    public void put(byte[] items) {
        for (byte item : items) {
            put(item);
        }
    }

    public byte get() {
        if (isEmpty()) {
            throw new RuntimeException("Ring buffer underflow");
        }
        byte item = buffer[indexTail];
        indexTail = (indexTail + 1) % buffer.length;
        return item;
    }

    @NotNull
    public Iterator<Byte> iterator() {
        return new RingBufferIterator();
    }

    // an iterator, doesn't implement remove() since it's optional
    private class RingBufferIterator implements Iterator<Byte> {
        private int i = 0;

        public boolean hasNext() {
            return i < size();
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }

        public Byte next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            return buffer[i++];
        }
    }
}