Authors:
Walter Savitch ,kenrick Mock
Chapter:
Generics And The Arraylist Class
Exercise:
Programming Projects
Question:4 | ISBN:9780132830317 | Edition: 5
Question
Write a generic class, MyMathClass, with a type parameter T where T is a numeric object type (e.g., Integer, Double, or any class that extends java.lang.Number ). Add a method named standardDeviation that takes an ArrayList of type T and returns as a double the standard deviation of the values in the ArrayList. Use the doubleValue () method in the Number class to retrieve the value of each number as a double. Refer to Programming Project 6.5 for a definition of computing the standard deviation. Test your method with suitable data. Your program should generate a compile-time error if your standard deviation method is invoked on an ArrayList that is defined for nonnumeric elements (e.g., Strings ).
Answer
public class MyMathClass<T extends Number>
{
public double standardDeviation(ArrayList<T> numbers)
{
double Average = 0;
for(int i = 0; i < n.size(); i++)
{
average += n.get(i).doubleValue();
}
Average /= n.size();
double stdDeviation = 0;
for(int j = 0; j < n.size(); j++)
{
stdDeviation += (n.get(j).doubleValue() – Average) *(n.get(j).doubleValue() – Average);
}
stdDeviation = Math.sqrt(stdDeviation / n.size());
return stdDeviation;
}
}
import java.util.*;
public class TestMath
{
public static void main(String args[])
{
ArrayList<Double> doublevalues = new ArrayList<Double>();
ArrayList<Integer> integers = new ArrayList<Integer>();
for(double i = 1; i < 5.5; i += 0.5)
doublevalues.add(i);
for(int j = 1; j < 10; j++)
integers.add(j);
MyMathClass<Double> object1 = new MyMathClass<Double>();
System.out.println("Standard deviation for double array: " + object1.standardDeviation(doublevalues));
MyMathClass<Integer> object2 = new MyMathClass<Integer>();
System.out.println("Standard deviation for integer array: " + object2.standardDeviation(integers));
}
}