CSC212 Example of Generic Pair Class & Exercise Solutions

--D. Thiebaut (talk) 12:07, 23 September 2014 (EDT)

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Non-Generic Pair Class

class PairInts {
    private int first;
    private int second;

    public PairInts( int f, int s ) {
        first = f;
        second = s;
    }

    public int getFirst() { return first; }
    public int getSecond() { return second; }
    public void setFirst( int f ) { first = f; }
    public void setSecond( int s ) { second = s; }
    public String toString( ) { return String.format( "(%d,%d)", first, second ); }
}

Test Class

class TestPairInts {
    static public void main( String[] args ) {
        PairInts p1 = null, p2 = null;

        p1 = new PairInts( 10, 3 );
        p2 = new PairInts( 5, -9 );

        System.out.println( "p1 = " + p1 );
        System.out.println( "p2 = " + p2 );
        p1.setFirst( p2.getSecond() );
        System.out.println( "p1 = " + p1 );
    }
}

Generic Pair Class

public class Pair<T, P> {
    private T first;
    private P second;

    public Pair( T f, P s ) {
        first = f;
        second = s;
    }

    public T getFirst() { return first; }
    public P getSecond() { return second; }
    public void setFirst( T f ) { first = f; }
    public void setSecond( P s ) { second = s; }
    public String toString( ) { return "(" + first + ", " + second + ")"; }
}

Test Class

class TestPair {
    static public void main( String[] args ) {
        Pair<int, int> p1 = null, p2 = null;

        p1 = new Pair<int, int>( 10, 3 );
        p2 = new Pair<int, int>( 5, -9 );

        System.out.println( "p1 = " + p1 );
        System.out.println( "p2 = " + p2 );
        p1.setFirst( p2.getSecond() );
        System.out.println( "p1 = " + p1 );
    }
}

Exercise 1

Problem

• Create an simple program that

• uses the PairInts class
• creates an array of 10 pairs, where the first number of the pair in a positive integer (random), and the second number is the fibonacci term equivalent to the first number. For example: (0, 1), (1, 1), (2, 2), (3, 3), (4, 5), (5, 8), (6, 13), etc.
• displays the array on the screen.

Exercise 1 Solution

public class Exercise1Pair {

	private static int fibAt( int index ) {
		if ( index==0 || index== 1 )
                     return 1;
                return fibAt( index-1 ) + fibAt( index-2 );
	}
	
	public static void main(String[] args) {
		// create the array of pairs
		PairInts[] A = new PairInts[10];
		
		// initialize it with different pairs
		for ( int i=0; i<10; i++ ) {
			int index = ( i * 2 );
			int fib = fibAt( index );
			A[ i ] = new PairInts( index, fib );
		}	
		
		// display the array
		for ( int i=0; i<10; i++ )
			System.out.println( String.format( "(%d,%d)", A[i].getFirst(),
					A[i].getSecond() ) );

	}

}

class PairInts {
    private int first;
    private int second;

    public PairInts( int f, int s ) {
        first = f;
        second = s;
    }

    public int getFirst() { return first; }
    public int getSecond() { return second; }
    public void setFirst( int f ) { first = f; }
    public void setSecond( int s ) { second = s; }
    public String toString( ) { 
		return String.format( "(%d,%d)", first, second ); }
}

Exercise 2

Problem

• Same as Exercise 1, but this time the program

• uses the generic Pair Class,
• creates an array of 10 pairs, where the first number of the pair in a positive integer (random), and the second number is the fibonacci term equivalent to the first number. For example: (0, 1), (1, 1), (2, 2), (3, 3), (4, 5), (5, 8), (6, 13), etc.
• displays the array on the screen.

Solution

public class Exercise2Pair {

	private static int fibAt( int index ) {
		if ( index==0 || index== 1 )
                     return 1;
                return fibAt( index-1 ) + fibAt( index-2 );
	}

	public static void main(String[] args) {
		// create the array of pairs
		Pair<Integer, Integer>[] A = new Pair[10];
		
		// initialize it with different pairs
		for ( int i=0; i<10; i++ ) {
			int index = ( i * 2 );
			int fib = fibAt( index );
			A[ i ] = new Pair<Integer, Integer>( index, fib );
		}	
		
		// display the array
		for ( int i=0; i<10; i++ )
			System.out.println( String.format( "(%d,%d)", A[i].getFirst(),
					A[i].getSecond() ) );

	}
}

class Pair<T, P> {
    private T first;
    private P second;

    public Pair( T f, P s ) {
        first = f;
        second = s;
    }

    public T getFirst() { return first; }
    public P getSecond() { return second; }
    public void setFirst( T f ) { first = f; }
    public void setSecond( P s ) { second = s; }
    public String toString( ) { 
			return "(" + first + ", " + second + ")"; }
}