Question

Q. Write a method add(PolyTerm): Two PolyTerm objects can be added if and only if they have the same exponent. If the calling object can be added to the parameter object, return their sum, otherwise (if they can't be added), return null. For example 2x^3 + -7.3x^3 = -5.3x^3 while 2x^3 + 8x^2 should return null.
(It's on JAVA)

The JUnit Test for this question is:

public class PolyTermTest {
   public static int score = 0;
   public static String result = "";
   public static String currentMethodName = null;
   ArrayList<String> methodsPassed = new ArrayList<String>();
  
   PolyTerm t1, t2, t3, t4;

   @BeforeEach
   public void setUp() throws Exception {
       currentMethodName = null;
       t1 = new PolyTerm(1, 1); //x
       t2 = new PolyTerm(2.4, 3); //2.4x^3
       t3 = new PolyTerm(-1.5, 0); //-1.5
       t4 = new PolyTerm(3.6, -2); //3.6x^-2
   }

@Test @Order(7) @Graded(marks=8, description="add(PolyTerm)")
   public void testAdd() {
       assertNull(t1.add(t2));
       assertNull(t1.add(t3));
       assertNull(t1.add(t4));
       assertNull(t2.add(t3));
       assertNull(t2.add(t4));
       assertNull(t3.add(t4));
      
       PolyTerm t5 = new PolyTerm(1.1, -2);
       assertNotNull(t4.add(t5));
       assertEquals(4.7, t4.add(t5).coefficient, 0.001);
       assertEquals(-2, t4.add(t5).exponent);

       currentMethodName = new Throwable().getStackTrace()[0].getMethodName();
   }

Answer 1

// Assuming Polyterm contains fields coefficient and exponent
public PolyTerm add(PolyTerm p)
{
   // exponents are same
   if(exponent == p.exponent)
       // create a new PolyTerm where coefficient = sum of this and p's coefficient and exponent = this's exponent
       return new PolyTerm(coefficient+p.coefficient, exponent); // Assuming PolyTerm contains a constructor that takes as inputs coefficient as first argument and exponent as secon argument

else // exponents are not same
       return null;
}