Computer Science 210
Data Structures
Fall 2019, Siena College
GenericPair BlueJ Project
Click here to download a BlueJ project for GenericPair.
GenericPair Source Code
The Java source code for GenericPair is below. Click on a file name to download it.
/**
* Example GenericPair: our pair structure, but now with type parameters
* to enforce consistency of the usage of a given instance of the class.
*
* @author Jim Teresco, The College of Saint Rose, CSC 523, Summer 2014
* CSIS 210, Siena College, Fall 2016, Fall 2017
* @version Fall 2019
*
*/
// First, notice that we now have "type parameters" after our class name.
// These tell us what kinds of objects we will use for the first (U), and
// second (V) values in our pair.
public class GenericPair<U,V> {
// our instance variables will be the generic types U and V
// which will be filled in with actual types when we create an
// instance of the class, much like an actual parameter gives
// a value to a formal parameter when a method is called.
private U first;
private V second;
// our constructor for a new GenericPair
// note that the formal parameter types are now
// the U and V types
/**
* Construct a new GenericPair
*
* @param first the first item in the pair
* @param second the second item in the pair
*/
public GenericPair(U first, V second) {
this.first = first;
this.second = second;
}
// accessors and mutators below also now use the generic types
/**
* Get the first item in the pair
*
* @return the first item in the pair
*/
public U getFirst() {
return first;
}
/**
* Get the second item in the pair
*
* @return the second item in the pair
*/
public V getSecond() {
return second;
}
/**
* Modify the first item in the pair
*
* @param newFirst the new first item in the pair
*/
public void setFirst(U newFirst) {
first = newFirst;
}
/**
* Modify the second item in the pair
*
* @param newSecond the new first item in the pair
*/
public void setSecond(V newSecond) {
second = newSecond;
}
/**
* Modify the second item in the pair
*
* @param newSecond the new first item in the pair
*/
public void setValues(U newFirst, V newSecond) {
first = newFirst;
second = newSecond;
}
/**
* Return a String to make this look like a coordinate pair (seems as
* good as anything and likely to be useful in many contexts).
* Note that we are implcitly using the toString methods of the
* objects we encapsulate.
*
* @return the objects in the pair, in parentheses separated by a comma
*/
@Override
public String toString() {
return "(" + first + ", " + second + ")";
}
/**
* Check for equality of this GenericPair with another, defined by both
* items in the pair being equal to those in the other pair.
*
* @param o the other GenericPair
* @return whether this GenericPair is equal to o
*/
@Override
public boolean equals(Object o) {
GenericPair<U,V> other = (GenericPair<U,V>)o;
return other.first.equals(first) && other.second.equals(second);
}
/**
* main method to run some test cases.
*
* @param args not used.
*/
public static void main(String args[]) {
// we'll create a few GenericPair objects and print them out
// note that we need to specify the actual types we
// intend to use for the first and second now, and where
// we want a primitive type, we must specify the "boxed"
// equivalent object type
GenericPair<String,Double> a = new GenericPair<String,Double>("Bob", 9.1);
GenericPair<String,Double> b = new GenericPair<String,Double>("Alice", 0.0);
System.out.println("a: " + a);
System.out.println("b: " + b);
// try out the accessors
System.out.println("a.getFirst(): " + a.getFirst());
System.out.println("a.getSecond(): " + a.getSecond());
System.out.println("b.getFirst(): " + b.getFirst());
System.out.println("b.getSecond(): " + b.getSecond());
// are they equal?
System.out.println("a.equals(b): " + a.equals(b));
// mutators!
a.setFirst("Charlie");
a.setSecond(-23.5);
b.setValues("Charlie", -23.5);
System.out.println("a: " + a);
System.out.println("b: " + b);
// are they equal now? Hope so!
System.out.println("a.equals(b): " + a.equals(b));
// and we can use other types too
GenericPair<Integer,String> c = new GenericPair<Integer,String>(2, "Jeter");
// uncomment the following to see what happens if we send
// the wrong type of object to the equals method
//System.out.println("a.equals(\"hi there\"): " + a.equals("high there"));
}
}