edu.princeton.cs.introcs

Class ST<Key extends Comparable<Key>,Value>

java.lang.Object

edu.princeton.cs.introcs.ST<Key,Value>

All Implemented Interfaces:

Iterable<Key>

public class ST<Key extends Comparable<Key>,Value>
extends Object
implements Iterable<Key>

The ST class represents an ordered symbol table of generic key-value pairs. It supports the usual put, get, contains, delete, size, and is-empty methods. It also provides ordered methods for finding the minimum, maximum, floor, and ceiling. It also provides a keys method for iterating over all of the keys. A symbol table implements the associative array abstraction: when associating a value with a key that is already in the symbol table, the convention is to replace the old value with the new value. Unlike Map, this class uses the convention that values cannot be null—setting the value associated with a key to null is equivalent to deleting the key from the symbol table.

This implementation uses a balanced binary search tree. It requires that the key type implements the Comparable interface and calls the compareTo() and method to compare two keys. It does not call either equals() or hashCode(). The put, contains, remove, minimum, maximum, ceiling, and floor operations each take logarithmic time in the worst case. The size, and is-empty operations take constant time. Construction takes constant time.

For additional documentation, see Section 4.4 of Introduction to Programming in Java: An Interdisciplinary Approach by Robert Sedgewick and Kevin Wayne.

Constructor Summary

Constructors

Constructor and Description
ST() Initializes an empty symbol table.

Method Summary

Methods

Modifier and Type	Method and Description
Key	ceil(Key key) Returns the smallest key in the symbol table greater than or equal to key.
boolean	contains(Key key) Does this symbol table contain the given key?
void	delete(Key key) Removes the key and associated value from the symbol table (if the key is in the symbol table).
Key	floor(Key key) Returns the largest key in the symbol table less than or equal to key.
Value	get(Key key) Returns the value associated with the given key.
boolean	isEmpty() Is this symbol table empty?
Iterator<Key>	iterator() Returns all of the keys in the symbol table as an iterator.
Iterable<Key>	keys() Returns all keys in the symbol table as an Iterable.
static void	main(String[] args) Unit tests the ST data type.
Key	max() Returns the largest key in the symbol table.
Key	min() Returns the smallest key in the symbol table.
void	put(Key key, Value val) Inserts the key-value pair into the symbol table, overwriting the old value with the new value if the key is already in the symbol table.
int	size() Returns the number of key-value pairs in this symbol table.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ST

public ST()

Initializes an empty symbol table.

Method Detail

get

public Value get(Key key)

Returns the value associated with the given key.

Parameters:

key - the key

Returns:

the value associated with the given key if the key is in the symbol table and null if the key is not in the symbol table

Throws:

NullPointerException - if key is null

put

public void put(Key key,
       Value val)

Inserts the key-value pair into the symbol table, overwriting the old value with the new value if the key is already in the symbol table. If the value is null, this effectively deletes the key from the symbol table.

Parameters:

key - the key

val - the value

Throws:

NullPointerException - if key is null

delete

public void delete(Key key)

Removes the key and associated value from the symbol table (if the key is in the symbol table).

Parameters:

key - the key

Throws:

NullPointerException - if key is null

contains

public boolean contains(Key key)

Does this symbol table contain the given key?

Parameters:

key - the key

Returns:

true if this symbol table contains key and false otherwise

Throws:

NullPointerException - if key is null

size

public int size()

Returns the number of key-value pairs in this symbol table.

Returns:

the number of key-value pairs in this symbol table

isEmpty

public boolean isEmpty()

Is this symbol table empty?

Returns:

true if this symbol table is empty and false otherwise

keys

public Iterable<Key> keys()

Returns all keys in the symbol table as an Iterable. To iterate over all of the keys in the symbol table named st, use the foreach notation: for (Key key : st.keys()).

Returns:

all keys in the sybol table as an Iterable

iterator

public Iterator<Key> iterator()

Returns all of the keys in the symbol table as an iterator. To iterate over all of the keys in a symbol table named st, use the foreach notation: for (Key key : st).

Specified by:

iterator in interface Iterable<Key extends Comparable<Key>>

Returns:

an iterator to all of the keys in the symbol table

min

public Key min()

Returns the smallest key in the symbol table.

Returns:

the smallest key in the symbol table

Throws:

NoSuchElementException - if the symbol table is empty

max

public Key max()

Returns the largest key in the symbol table.

Returns:

the largest key in the symbol table

Throws:

NoSuchElementException - if the symbol table is empty

ceil

public Key ceil(Key key)

Returns the smallest key in the symbol table greater than or equal to key.

Parameters:

key - the key

Returns:

the smallest key in the symbol table greater than or equal to key

Throws:

NoSuchElementException - if the symbol table is empty

NullPointerException - if key is null

floor

public Key floor(Key key)

Returns the largest key in the symbol table less than or equal to key.

Parameters:

key - the key

Returns:

the largest key in the symbol table less than or equal to key

Throws:

NoSuchElementException - if the symbol table is empty

NullPointerException - if key is null

main

public static void main(String[] args)

Unit tests the ST data type.