The IntList class describes immutable linked lists of integers. An integer list is defined recursively as either

• the empty list, or
• a (non-empty) list node with a head component that is an integer and a tail component that is another integer list.

Integer lists are immutable in the sense that the head or tail of a list node cannot be changed after the list node has been created (via the prepend() method).

There are no public constructor or instance methods for integer lists; they are created and manipulated by the following class methods:

Class Methods

public static IntList empty()
Returns an empty integer list. IntList.empty() behaves like new IntList().

public static IntList prepend (int n, IntList L)
Returns a new integer list node whose head is n and whose tail is L. IntList.prepend(n,L) is equivalent to new IntList(n, L).

public static boolean isEmpty (IntList L)
Returns true if L is an empty integer list node and false if L is a nonempty integer list node.

public static int head (IntList L)
Returns the integer that is the head component of the integer list node L. Signals an exception if L is empty.

public static IntList tail (IntList L)
Returns the integer list that is the tail component of the integer list node L. Signals an exception if L is empty.

public static boolean equals (IntList L1, IntList L2)
Returns true if L1 and L2 have the same length and the same elements in the same order; otherwise returns false. Note that the equals method behaves differently than == on lists, which determines if two list nodes were created by the same call to prepend. For instance, if L is the list [1,2,3], then L.equals(prepend(1,tail(L))) is true, but L == prepend(1,tail(L)) is false.

public static String toString (IntList L)
Returns a string representation of of the integer list L in which the integer list elements are separated by commas and delimited by square brackets. For example, if L1 is a list containing the sequence of integers 6, -17 and 42, then toString(L1) returns "[6,-17,42]".

public static IntList fromString (String s)
If s is the printed representation of an integer list (i.e., comma separated integers delimited by square brackets), returns an IntList with that representation. For example, fromString("[7,-2,4]") returns an 3-element integer list with elements 7, -2, and 4. If s is not the printed representation of an integer list, signals an error.