Cell.java

package org.evryword;

import java.util.Objects;

public class Cell {
    public char content = ' ';
    public Cell next;
    public Cell prev;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Cell cell = (Cell) o;
        return content == cell.content && Objects.equals(next, cell.next) && Objects.equals(prev, cell.prev);
    }

    @Override
    public int hashCode() {
        return Objects.hash(content, next, prev);
    }
}

Main.java

package org.evryword;

public class Main {
    public static void main(String[] args) {

        // INFO START A TAPE
        Tape myTape = new Tape();
        myTape.setContent('a');

        myTape.moveLeft();
        myTape.setContent('b');

        myTape.moveLeft();
        myTape.setContent('c');

        myTape.moveLeft();
        myTape.setContent('d');

        myTape.moveRight();
        myTape.setContent('9');

        myTape.moveRight();
        myTape.setContent('8');

        myTape.moveRight();
        myTape.setContent('7');

        System.out.println("[getTail] " + myTape.getTail(myTape.getCurrentCell()).content);
        System.out.println("[getHead] " + myTape.getHead(myTape.getCurrentCell()).content);

        String tapeContents = myTape.getTapeContents();
        System.out.println("[tapeContents] " + tapeContents);
    }
}

Tape.java

package org.evryword;

public class Tape {
    public Cell currentCellPointer;

    public Tape() {
        final Cell newCell = new Cell();
        currentCellPointer = newCell;
    }

    public Cell getCurrentCell() {
        return currentCellPointer;
    }

    public char getContent() {
        return currentCellPointer.content;
    }

    public void setContent(char ch) {
        currentCellPointer.content = ch;
    }

    public void moveLeft() {
        // INFO Traverse to get the size of the list
        final Cell cell = new Cell();
        final Cell tail = getTail(currentCellPointer);

        currentCellPointer.next = cell;
        cell.prev = tail;
        currentCellPointer = cell;
    }

    public Cell getTail(Cell cell) {
        return cell.next == null ? cell : getTail(cell.next);
    }

    public Cell getHead(Cell cell) {
        return cell.prev == null ? cell : getHead(cell.prev);
    }

    public void moveRight() {
        // INFO If cell is rightmost, create new cell and added to tape at the right of the tape
        // INFO Find last cell
        final Cell cell = new Cell();
        final Cell head = getHead(currentCellPointer);

        currentCellPointer.prev = cell;
        cell.next = head;
        currentCellPointer = cell;
    }

    public String getTapeContents() {
        Cell currentCell = getHead(currentCellPointer);
        // INFO Traverse list to get all contents
        return readTapeContents(currentCell);
    }

    // INFO a -> b -> c -> d -> e
    public String readTapeContents(Cell cell) {
        if (cell == null) return "";
        return cell.content + readTapeContents(cell.next);
    }
}