Chapter 6:  "Collection Considerations"

Data Structures with Java, Rick Mercer

Answers to Self-Check Questions


6-1 which have errors? c and d
	  -c- can not assign a Double to an Intger
	  -d- can not assign an Object to an Intger
	
6-2 which are valid?  a, b, and c
	  -d- error
	  -e- error
	
6-3 which generate errors? None
	
6-4 test method for remove

    @Test
    public void testRemove() {
        Bag<String> names = new ArrayBag<String>();
        names.add("Sam");
        names.add("Chris");
        names.add("Devon");
        names.add("Sandeep");

        assertFalse(names.remove("Not here"));

        assertTrue(names.remove("Sam"));
        assertEquals(0, names.occurencesOf("Sam"));
        // Attempt to remove after remove
        assertFalse(names.remove("Sam"));
        assertEquals(0, names.occurencesOf("Sam"));

        assertEquals(1, names.occurencesOf("Chris"));
        assertTrue(names.remove("Chris"));
        assertEquals(0, names.occurencesOf("Chris"));

        assertEquals(1, names.occurencesOf("Sandeep"));
        assertTrue(names.remove("Sandeep"));
        assertEquals(0, names.occurencesOf("SanDeep"));

        // Only 1 left
        assertEquals(1, names.occurencesOf("Devon"));
        assertTrue(names.remove("Devon"));
        assertEquals(0, names.occurencesOf("Devon"));
    }

	
6-5 remove method in the ArrayBag class

  // Remove element if it is in this bag, otherwise return false.
  public boolean remove(E element) {
  
      for (int i = 0; i < n; i++) {
          if (element.equals(data[i])) {
              // Replace with the element at the send
              data[i] = data[n - 1];
              // Reduce the size
              n--;
              return true;  // Found--end the search
          }
    }
    
    // Did not find element "equals" anything in this bag.
    return false;
  }

	
6-6 O(n)

6-7 anObject = aString;    // __x___
    anInteger = aString;   // Can't assign String to Integer
    anObject = anInteger;  // __x___
    anInteger = anObject;  // Can;t assign Obect to Integer

6-8 All compile

6-9 Integer i = 3;                         // ___x_____
    int i2 = new Integer(3);               // ___x_____
    Integer i3 = 3.5;                      // Can't assign Double to Integer
    int i4 = 3 * new Integer(5);           // ____x____
    Double d2 = 3.0 * new Integer(3) / 4;  // ____x____
    Double d = 3;                          // Need 3.0 rather than 3