CS 61B Lab 4 February 13-14, 2014 Goal: This lab will demonstrate how a sentinel node can simplify a doubly-linked list implementation. Copy the Lab 4 directory by starting from your home directory and typing: cp -r ~cs61b/lab/lab4 . cd lab4 Getting Started --------------- Please make sure you have a partner for this lab. The files in the lab4 directory contain classes for two different types of doubly-linked list. The DList1 class does not use a sentinel, whereas the DList2 class does. The DList1 class is not circularly linked, but the DList2 class is (through the sentinel). Compile DList1.java and DList2.java (using "javac -g DList1.java DList2.java".) Your task is to implement two insertFront() and two removeFront() methods--one of each for each list class. insertFront() and removeFront() insert or remove an item at the beginning of a list. Make sure your implementations work for empty lists, one-node lists, and larger lists. The main() methods of DList1 and DList2 include test code, which you can run with "java DList1" and "java DList2". Part I: insertFront in DList1 (1 point) ---------------------------------------- Write a method called DList1.insertFront() that inserts an int at the front of "this" DList1. Part II: removeFront in DList1 (1 point) ----------------------------------------- Write a method called DList1.removeFront() that removes the first item (and node) from "this" DList1. Part III: insertFront in DList2 (1 point) ------------------------------------------ Write a method called DList2.insertFront() that inserts an int at the front of "this" DList2. Your code should NOT use any "if" statements or conditionals. Part IV: removeFront in DList2 (2 points) ------------------------------------------ Write a method called DList2.removeFront() that removes the first item (and non-sentinel node) from "this" DList2. Your code should not require separate branches for the one-node case and the more-than-one-node case. (You will need one "if", to handle the zero-node case.) Check-off --------- Run the DList1 and DList2 test code for your TA or Lab Assistant. 1 point: DList1.insertFront(). 1 point: DList1.removeFront(). 1 point: DList2.insertFront(). 1 point: DList2.removeFront().