structure5
Class Association<K,V>

java.lang.Object
  structure5.Association<K,V>

All Implemented Interfaces:

java.util.Map.Entry<K,V>

Direct Known Subclasses:

ComparableAssociation, HashAssociation

public class Association<K,V>
extends java.lang.Object
implements java.util.Map.Entry<K,V>

A class implementing a key-value pair. This class associates an immutable key with a mutable value. Used in many other structures.

Example Usage:

To store the number of classes a student has taken from five different professors and to output this information, we could use the following.

 public static void main(String[] argv){
      //store the number of classes taken by the student in an array of associations
      Association [] classesTaken = new Association[5];
      classesTaken[0] = new Association("Andrea", new Integer(5));
      classesTaken[1] = new Association("Barbara", new Integer(1));
      classesTaken[2] = new Association("Bill", new Integer(3));
      classesTaken[3] = new Association("Duane", new Integer(2));
      classesTaken[4] = new Association("Tom", new Integer(1));

      //print out each item in the array
      for (int i = 0; i< classesTaken.length; i++){
          System.out.println("This Student has taken " + classesTaken[i].getValue() +
                             " classes from " + classesTaken[i].getKey()+ ".");
      }
 }
 

Field Summary

protected K	theKey The immutable key.
protected V	theValue The mutable value.

Constructor Summary

Association(K key)
Constructs a pair from a key; value is null.

Association(K key, V value)
Constructs a pair from a key and value.

Method Summary

boolean	equals(java.lang.Object other) Standard comparison function.
K	getKey() Fetch key from association.
V	getValue() Fetch value from association.
int	hashCode() Standard hashcode function.
V	setValue(V value) Sets the value of the key-value pair.
java.lang.String	toString() Standard string representation of an association.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

theKey

protected K theKey

The immutable key. An arbitrary object.

theValue

protected V theValue

The mutable value. An arbitrary object.

Constructor Detail

Association

public Association(K key,
                   V value)

Constructs a pair from a key and value.

Parameters:

key - A non-null object.

value - A (possibly null) object.

Precondition:

key is non-null

Postcondition:

constructs a key-value pair

Association

public Association(K key)

Constructs a pair from a key; value is null.

Parameters:

key - A non-null key value.

Precondition:

key is non-null

Postcondition:

constructs a key-value pair; value is null

Method Detail

equals

public boolean equals(java.lang.Object other)

Standard comparison function. Comparison based on keys only.

Specified by:

equals in interface java.util.Map.Entry<K,V>

Overrides:

equals in class java.lang.Object

Parameters:

other - Another association.

Returns:

true iff the keys are equal.

Precondition:

other is non-null Association

Postcondition:

returns true iff the keys are equal

hashCode

public int hashCode()

Standard hashcode function.

Specified by:

hashCode in interface java.util.Map.Entry<K,V>

Overrides:

hashCode in class java.lang.Object

Returns:

A hash code for association.

See Also:

Hashtable

Postcondition:

return hash code association with this association

getValue

public V getValue()

Fetch value from association. May return null.

Specified by:

getValue in interface java.util.Map.Entry<K,V>

Returns:

The value field of the association.

Postcondition:

returns value from association

getKey

public K getKey()

Fetch key from association. Should not return null.

Specified by:

getKey in interface java.util.Map.Entry<K,V>

Returns:

Key of the key-value pair.

Postcondition:

returns key from association

setValue

public V setValue(V value)

Sets the value of the key-value pair.

Specified by:

setValue in interface java.util.Map.Entry<K,V>

Parameters:

value - The new value.

Postcondition:

sets association's value to value

toString

public java.lang.String toString()

Standard string representation of an association.

Overrides:

toString in class java.lang.Object

Returns:

String representing key-value pair.

Postcondition:

returns string representation