ST.java


Below is the syntax highlighted version of ST.java from §4.4 Symbol Tables.


/******************************************************************************
 *  Compilation:  javac ST.java
 *  Execution:    java ST
 *  Dependencies: StdIn.java StdOut.java
 *  
 *  Sorted symbol table implementation using a java.util.TreeMap.
 *  Does not allow duplicates.
 *
 *  % java ST
 *
 ******************************************************************************/

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.TreeMap;

/**
 *  The {@code ST} class represents an ordered symbol table of generic
 *  key-value pairs.
 *  It supports the usual <em>put</em>, <em>get</em>, <em>contains</em>,
 *  <em>remove</em>, <em>size</em>, and <em>is-empty</em> methods.
 *  It also provides ordered methods for finding the <em>minimum</em>,
 *  <em>maximum</em>, <em>floor</em>, and <em>ceiling</em>.
 *  It also provides a <em>keys</em> method for iterating over all of the keys.
 *  A symbol table implements the <em>associative array</em> 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 {@link java.util.Map}, this class uses the convention that
 *  values cannot be {@code null}—setting the
 *  value associated with a key to {@code null} is equivalent to deleting the key
 *  from the symbol table.
 *  <p>
 *  This implementation uses a balanced binary search tree. It requires that
 *  the key type implements the {@code Comparable} interface and calls the
 *  {@code compareTo()} and method to compare two keys. It does not call either
 *  {@code equals()} or {@code hashCode()}.
 *  The <em>put</em>, <em>contains</em>, <em>remove</em>, <em>minimum</em>,
 *  <em>maximum</em>, <em>ceiling</em>, and <em>floor</em> operations each take
 *  logarithmic time in the worst case.
 *  The <em>size</em>, and <em>is-empty</em> operations take constant time.
 *  Construction takes constant time.
 *  <p>
 *  For additional documentation, see <a href="http://introcs.cs.princeton.edu/44st">Section 4.4</a> of
 *  <i>Introduction to Programming in Java: An Interdisciplinary Approach</i> by Robert Sedgewick and Kevin Wayne. 
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 *
 *  @param <Key> the generic type of keys in this symbol table
 *  @param <Value> the generic type of values in this symbol table
 */
public class ST<Key extends Comparable<Key>, Value> implements Iterable<Key> {

    private TreeMap<Key, Value> st;

    /**
     * Initializes an empty symbol table.
     */
    public ST() {
        st = new TreeMap<Key, Value>();
    }


    /**
     * Returns the value associated with the given key in this symbol table.
     *
     * @param  key the key
     * @return the value associated with the given key if the key is in this symbol table;
     *         {@code null} if the key is not in this symbol table
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public Value get(Key key) {
        if (key == null) throw new IllegalArgumentException("called get() with null key");
        return st.get(key);
    }

    /**
     * Inserts the specified key-value pair into the symbol table, overwriting the old 
     * value with the new value if the symbol table already contains the specified key.
     * Removes the specified key (and its associated value) from this symbol table
     * if the specified value is {@code null}.
     *
     * @param  key the key
     * @param  val the value
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public void put(Key key, Value val) {
        if (key == null) throw new IllegalArgumentException("called put() with null key");
        if (val == null) st.remove(key);
        else             st.put(key, val);
    }

    /**
     * Removes the specified key and its associated value from this symbol table     
     * (if the key is in this symbol table).
     *
     * @param  key the key
     * @throws IllegalArgumentException if {@code key} is {@code null}
     * @deprecated Replaced by {@link remove()}.
     */
    @Deprecated
    public void delete(Key key) {
        if (key == null) throw new IllegalArgumentException("called delete() with null key");
        st.remove(key);
    }

    /**
     * Removes the specified key and its associated value from this symbol table     
     * (if the key is in this symbol table).
     *
     * @param  key the key
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public void remove(Key key) {
        if (key == null) throw new IllegalArgumentException("called remove() with null key");
        st.remove(key);
    }

    /**
     * Returns true if this symbol table contain the given key.
     *
     * @param  key the key
     * @return {@code true} if this symbol table contains {@code key} and
     *         {@code false} otherwise
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public boolean contains(Key key) {
        if (key == null) throw new IllegalArgumentException("called contains() with null key");
        return st.containsKey(key);
    }

    /**
     * Returns the number of key-value pairs in this symbol table.
     *
     * @return the number of key-value pairs in this symbol table
     */
    public int size() {
        return st.size();
    }

    /**
     * Returns true if this symbol table is empty.
     *
     * @return {@code true} if this symbol table is empty and {@code false} otherwise
     */
    public boolean isEmpty() {
        return size() == 0;
    }

    /**
     * Returns all keys in this symbol table.
     * <p>
     * To iterate over all of the keys in the symbol table named {@code st},
     * use the foreach notation: {@code for (Key key : st.keys())}.
     *
     * @return all keys in this symbol table
     */
    public Iterable<Key> keys() {
        return st.keySet();
    }

    /**
     * Returns all of the keys in this symbol table.
     * To iterate over all of the keys in a symbol table named {@code st}, use the
     * foreach notation: {@code for (Key key : st)}.
     *
     * @return an iterator to all of the keys in this symbol table
     * @deprecated Replaced by {@link #keys()}.
     */
    @Deprecated
    public Iterator<Key> iterator() {
        return st.keySet().iterator();
    }

    /**
     * Returns the smallest key in this symbol table.
     *
     * @return the smallest key in this symbol table
     * @throws NoSuchElementException if this symbol table is empty
     */
    public Key min() {
        if (isEmpty()) throw new NoSuchElementException("called min() with empty symbol table");
        return st.firstKey();
    }

    /**
     * Returns the largest key in this symbol table.
     *
     * @return the largest key in this symbol table
     * @throws NoSuchElementException if this symbol table is empty
     */
    public Key max() {
        if (isEmpty()) throw new NoSuchElementException("called max() with empty symbol table");
        return st.lastKey();
    }

    /**
     * Returns the smallest key in this symbol table greater than or equal to {@code key}.
     *
     * @param  key the key
     * @return the smallest key in this symbol table greater than or equal to {@code key}
     * @throws NoSuchElementException if there is no such key
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public Key ceiling(Key key) {
        if (key == null) throw new IllegalArgumentException("called ceiling() with null key");
        Key k = st.ceilingKey(key);
        if (k == null) throw new NoSuchElementException("all keys are less than " + key);
        return k;
    }

    /**
     * Returns the largest key in this symbol table less than or equal to {@code key}.
     *
     * @param  key the key
     * @return the largest key in this symbol table less than or equal to {@code key}
     * @throws NoSuchElementException if there is no such key
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public Key floor(Key key) {
        if (key == null) throw new IllegalArgumentException("called floor() with null key");
        Key k = st.floorKey(key);
        if (k == null) throw new NoSuchElementException("all keys are greater than " + key);
        return k;
    }

    /**
     * Unit tests the {@code ST} data type.
     */
    public static void main(String[] args) {
        ST<String, Integer> st = new ST<String, Integer>();
        for (int i = 0; !StdIn.isEmpty(); i++) {
            String key = StdIn.readString();
            st.put(key, i);
        }
        for (String s : st.keys())
            StdOut.println(s + " " + st.get(s));
    }
}


Copyright © 2000–2016, Robert Sedgewick and Kevin Wayne.
Last updated: Sat Dec 3 23:27:03 EST 2016.