Stats.java

package hw4;

import java.util.HashMap;

public class Stats {
 
	public static HashMap<String, Object> computeStats (int [ ] numbers){
	     int length = numbers.length;
	     double med, var, sd, mean, sum, varsum;  
	     
	    //to capture state rather than print to stdout
	     HashMap<String, Object> stats = new HashMap<String, Object>(); 
	     
	     sum = 0;
	     for (int i = 0; i < length; i++)
	     {
	          sum += numbers [ i ];
	     }
	     med   = numbers [ length / 2 ] ; //assumes sorted array of length > 2 with no duplicates
	     mean = sum / (double) length; 
	     varsum = 0;
	     
	     for (int i = 0; i < length; i++)
	     {
	          varsum = varsum  + ((numbers [ i ] - mean) * (numbers [ i ] - mean));
	     }
	     
	     //With an array of length 1, both var and sd return NaN because length will be 1 and varsum/length-1 = NaN
	     var = varsum / ( length - 1.0 );
	     sd  = Math.sqrt ( var );

	     stats.put("length", length);
	     stats.put("mean", mean);
	     stats.put("median", med);
	     stats.put("variance", var);
	     stats.put("standard-deviation", sd);
	          
	     return stats;
	}

	
}

StatsTest.java

package hw4;
 
import java.util.Arrays;
import java.util.HashMap;
import junit.framework.Assert;
import org.junit.Before;
import org.junit.Test;
 
 
public class StatsTest {
 
Stats stats;
HashMap<String,Object> actual;
HashMap<String,Object> expected;
 
@Before
public void setUp(){
expected = new HashMap<String, Object>();
}
 
@Test
public void findMedianFromSortedArrayofInts(){
//@Pre - array has no duplicates
int[] nums = {3,2,0,-12,9,8,8,3,2};
Arrays.sort(nums);
        int med = nums[ nums.length/2 ]; //median logic in example
        System.out.println( Arrays.toString(nums) );
        System.out.println( med );
        Assert.assertEquals(3, med);
 
}
 
/**
* Test method for {@link hw4.Stats#computeStats(int[])}.
*/
@Test
public void testComputeStatsWith44() {
int[] numbers = {44};
actual = Stats.computeStats(numbers);
System.out.println(actual);
expected.put("median", 44.0);
Assert.assertEquals(expected.get("median"), actual.get("median"));
}
 
 
@Test
public void testComputeStatsWith2Nums() {
int[] numbers = {44,22};
actual = Stats.computeStats(numbers);
System.out.println(actual);
Assert.fail();
}
 
 
 
@Test
public void testComputeStatsWith3Nums() {
int[] numbers = {2,10,15};
actual = Stats.computeStats(numbers);
System.out.println(actual);
expected.put("median", 10.0);
expected.put("mean",9.0);
Assert.assertEquals(expected.get("mean"), actual.get("mean"));
 
}
 
@Test(expected=ArrayIndexOutOfBoundsException.class)
public void testComputeStatsWithEmptyArray() {
int[] numbers = {};
actual = Stats.computeStats(numbers);
}
 
@Test(expected=NullPointerException.class)
public void testComputeStatsWithNullArray() {
int[] numbers = null;
actual = Stats.computeStats(numbers);
System.out.println(actual);
}
 
 
 
 
 
}