structure
Class Association

java.lang.Object
  |
  +--structure.Association

All Implemented Interfaces:

java.util.Map.Entry

Direct Known Subclasses:

ComparableAssociation

public class Association

extends java.lang.Object

implements java.util.Map.Entry

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 java.lang.Object	theKey The immutable key.
protected java.lang.Object	theValue The mutable value.

Constructor Summary

Association(java.lang.Object key)
Constructs a pair from a key; value is null.

Association(java.lang.Object key, java.lang.Object value)
Constructs a pair from a key and value.

Method Summary

boolean	equals(java.lang.Object other) Standard comparison function.
java.lang.Object	getKey() Fetch key from association.
java.lang.Object	getValue() Fetch value from association.
int	hashCode() Standard hashcode function.
java.lang.Object	setValue(java.lang.Object 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 java.lang.Object theKey

The immutable key. An arbitrary object.

theValue

protected java.lang.Object theValue

The mutable value. An arbitrary object.

Constructor Detail

Association

public Association(java.lang.Object key,
                   java.lang.Object value)

Constructs a pair from a key and value.

Parameters:

key - A non-null object.

value - A (possibly null) object.

Association

public Association(java.lang.Object key)

Constructs a pair from a key; value is null.

Parameters:

key - A non-null key value.

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

Overrides:

equals in class java.lang.Object

Parameters:

other - Another association.

Returns:

true iff the keys are equal.

hashCode

public int hashCode()

Standard hashcode function.

Specified by:

hashCode in interface java.util.Map.Entry

Overrides:

hashCode in class java.lang.Object

Returns:

A hash code for association.

See Also:

Hashtable

getValue

public java.lang.Object getValue()

Fetch value from association. May return null.

Specified by:

getValue in interface java.util.Map.Entry

Returns:

The value field of the association.

getKey

public java.lang.Object getKey()

Fetch key from association. Should not return null.

Specified by:

getKey in interface java.util.Map.Entry

Returns:

Key of the key-value pair.

setValue

public java.lang.Object setValue(java.lang.Object value)

Sets the value of the key-value pair.

Specified by:

setValue in interface java.util.Map.Entry

Parameters:

value - The new 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.