BigInteger.java

public class BigInteger {
  DigitNode front;
  private static class DigitNode {
    int digit;
    DigitNode next;
    public DigitNode(int digit) {
      this.digit = digit;
      this.next = null;
    }
    public DigitNode(int digit, DigitNode next) {
      this.digit = digit;
      this.next = next;
    }
    public String toString(){
      String out = "";
      DigitNode cur = this;
      while(cur != null) {
        out += "(" + cur.digit + ") -> ";
        cur = cur.next;
      }
      return out;
    }
  }
  public BigInteger append(int d){
    DigitNode cur = this.front;
    while(cur.next != null) {
      cur = cur.next;
    }
    cur.next = new DigitNode(d);
    return this;
  }
  public String toString(){
    return this.front.toString();
  }
  public static void main(String[] args) {
    BigInteger b = new BigInteger();
    b.front = new DigitNode(1, new DigitNode(2, new DigitNode(3, new DigitNode(4, new DigitNode(5)))));
    System.out.println(b);
    System.out.println(b.append(6));
  }
}