How to understand the expression when writing values ​​to the output stream?

Question

Java

Why is this expression used in the writePoint() method? How then, when reading, get back the value of x and y, if only one value is written?
int value = point.getX() << 4 | point.getY();

class Point {
    private final int x;
    private final int y;

    public Point(int x, int y) {
        if (x < 0 || 15 < x) {
            throw new IllegalArgumentException();
        }

        if (y < 0 || 15 < y) {
            throw new IllegalArgumentException();
        }

        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    @Override
    public String toString() {
        return "Point(" + x + ", " + y + ")";
    }
}

class EntityOutputStream implements EntityOutput {
    private final DataOutput out;

    public EntityOutputStream(OutputStream out) {
        this.out = new DataOutputStream(out);
    }

    @Override
    public void writePoint(Point point) throws IOException {
        int value = point.getX() << 4 | point.getY();

        out.writeByte(value);
    }
}

public class App {
    public static void main(String[] args) throws IOException {
        Point point = new Point(11, 14);

        EntityOutputStream out = new EntityOutputStream(new FileOutputStream("c://file.txt"));
        EntityInput in = new EntityInputStream(new FileInputStream("c://file.txt"));

        out.writePoint(point);

        System.out.println(in.readPoint());
    }
}