Practice-It

You have been asked to extend the ArrayIntList class that we have been studying. Recall that it includes the following public constructors and methods:

You are to define a new class called HistoryList that extends this class through inheritance. It should behave like an ArrayIntList except that it should keep track of the history of modifications to the list. This history is stored as a sequence of String values indicating the list's state at each point. For example, if the operations below at left are performed, then the HistoryList object should keep track of the sequence of strings shown below at right:

HistoryList list = new HistoryList();
list.add(18);
list.add(27);
list.add(0, 45);
list.remove(1);
list.set(0, -15);
list.add(9);

"[]"
"[18]"
"[18, 27]"
"[45, 18, 27]"
"[45, 27]"
"[-15, 27]"
"[-15, 27, 9]"

When a HistoryList is constructed, the first string in the list above should be added to its history. Each time any of methods add, remove, or set are called, a new entry is added to the history showing the state of the list after the call. You must exactly reproduce the format shown above.

These strings that are part of the history will be accessed by clients using the following new methods:

In the example above, after executing the sample code, the history size will be 6 and the six different history strings can be accessed by calls on getHistory passing indexes between 0 and 5. For example:

for (int i = 0; i < list.historySize(); i++) {
    System.out.println(list.history(i));
}

You must also make HistoryList objects comparable to each other using the Comparable interface. A HistoryList with more strings in its history is considered to be "greater than" one with fewer history entries. If two HistoryLists have the same number of history entries, the one that contains more elements (the one with the greater size) is considered to be greater. If the two lists have the same number of history entries and the same size, they are considered to be "equal" for this problem.