Question

Please help complete the items marked TODO in the code and get the tests to pass:

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class TestIterator {

  private List<Integer> list;
  // See the Java List Interface documentation to understand what all the List methods do ...

  @Before
  public void setUp() throws Exception {
    list = new ArrayList<Integer>();
    // TODO also try with a LinkedList - does it make any difference?
  }

  @After
  public void tearDown() throws Exception {
    list = null;
  }

  @Test
  public void testEmpty() {
    final Iterator<Integer> i = list.iterator();
    assertFalse(i.hasNext());
  }

  @Test
  public void testNonempty() {
    list.add(33);
    list.add(77);
    list.add(44);
    list.add(77);
    list.add(55);
    list.add(77);
    list.add(66);
    final Iterator<Integer> i = list.iterator();
    assertTrue(i.hasNext());
    assertEquals(33, i.next().intValue());
    // TODO fix the expected values in the assertions below
    assertTrue(i.hasNext());
    assertEquals(0, i.next().intValue());
    assertTrue(i.hasNext());
    assertEquals(0, i.next().intValue());
    assertTrue(i.hasNext());
    assertEquals(0, i.next().intValue());
    assertTrue(i.hasNext());
    assertEquals(0, i.next().intValue());
    assertTrue(i.hasNext());
    assertEquals(0, i.next().intValue());
    assertTrue(i.hasNext());
    assertEquals(0, i.next().intValue());
    assertFalse(i.hasNext());
  }

  @Test
  public void testRemove() {
    list.add(33);
    list.add(77);
    list.add(44);
    list.add(77);
    list.add(55);
    list.add(77);
    list.add(66);
    final Iterator<Integer> i = list.iterator();
    while (i.hasNext()) {
      if (i.next() == 77) {
        i.remove(); // TODO what happens if you use list.remove(Integer.valueOf(77))?
      }
    }
    // TODO using assertEquals and Arrays.asList, express which values are left in the list
    // See TestList.java for examples of how to use Arrays.asList; also see the Java Arrays
    // class for more information
    fail("Not yet implemented"); // remove this line when done
  }

  @Test
  public void testAverageValues() {
    list.add(33);
    list.add(77);
    list.add(44);
    list.add(77);
    list.add(55);
    list.add(77);
    list.add(66);
    double sum = 0;
    int n = 0;
    // TODO use an iterator and a while loop to compute the average (mean) of the values
    // (defined as the sum of the items divided by the number of items)
    // testNonempty shows how to use an iterator; use i.hasNext() in the while loop condition
    assertEquals(61.3, sum / n, 0.1);
    assertEquals(7, n);
  }
}

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

// TestIterator.java

import static org.junit.Assert.assertEquals;

import static org.junit.Assert.assertFalse;

import static org.junit.Assert.assertTrue;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Iterator;

import java.util.LinkedList;

import java.util.List;

import org.junit.After;

import org.junit.Before;

import org.junit.Test;

public class TestIterator {

      private List<Integer> list;

      // See the Java List Interface documentation to understand what all the List

      // methods do ...

      @Before

      public void setUp() throws Exception {

            list = new ArrayList<Integer>();

            // TODO also try with a LinkedList - does it make any difference?

            list = new LinkedList<Integer>(); // no difference

      }

      @After

      public void tearDown() throws Exception {

            list = null;

      }

      @Test

      public void testEmpty() {

            final Iterator<Integer> i = list.iterator();

            assertFalse(i.hasNext());

      }

      @Test

      public void testNonempty() {

            list.add(33);

            list.add(77);

            list.add(44);

            list.add(77);

            list.add(55);

            list.add(77);

            list.add(66);

            final Iterator<Integer> i = list.iterator();

            assertTrue(i.hasNext());

            assertEquals(33, i.next().intValue());

            // TODO fix the expected values in the assertions below

            assertTrue(i.hasNext());

            assertEquals(77, i.next().intValue());

            assertTrue(i.hasNext());

            assertEquals(44, i.next().intValue());

            assertTrue(i.hasNext());

            assertEquals(77, i.next().intValue());

            assertTrue(i.hasNext());

            assertEquals(55, i.next().intValue());

            assertTrue(i.hasNext());

            assertEquals(77, i.next().intValue());

            assertTrue(i.hasNext());

            assertEquals(66, i.next().intValue());

            assertFalse(i.hasNext());

      }

      @Test

      public void testRemove() {

            list.add(33);

            list.add(77);

            list.add(44);

            list.add(77);

            list.add(55);

            list.add(77);

            list.add(66);

            final Iterator<Integer> i = list.iterator();

            while (i.hasNext()) {

                  if (i.next() == 77) {

                        i.remove(); // TODO what happens if you use

                                           // list.remove(Integer.valueOf(77))?

                        // if you use list.remove(Integer.valueOf(77)) while iterating,

                        // it will throw ConcurrentModificationException next time the

                        // iterator is used.

                  }

            }

            // TODO using assertEquals and Arrays.asList, express which values are

            // left in the list

            // See TestList.java for examples of how to use Arrays.asList; also see

            // the Java Arrays

            // class for more information

            assertEquals(Arrays.asList(33, 44, 55, 66), list);

      }

      @Test

      public void testAverageValues() {

            list.add(33);

            list.add(77);

            list.add(44);

            list.add(77);

            list.add(55);

            list.add(77);

            list.add(66);

            double sum = 0;

            int n = 0;

            // TODO use an iterator and a while loop to compute the average (mean)

            // of the values

            // (defined as the sum of the items divided by the number of items)

            // testNonempty shows how to use an iterator; use i.hasNext() in the

            // while loop condition

            Iterator<Integer> it = list.iterator(); // getting iterator

            while (it.hasNext()) {

                  // adding next item to sum

                  sum += it.next().intValue();

                  // incrementing n

                  n++;

            }

            assertEquals(61.3, sum / n, 0.1);

            assertEquals(7, n);

      }

}

/*OUTPUT of JUnit test case*/