CS111 IntList Contract

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).

Constructor Methods

public IntList ()
Constructs an empty integer list.

public IntList (int n, IntList L)
Constructs a new integer list node whose head is n and whose tail is L.

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.