Do this...
Create a test-case class named
Experiment04Test.
In addition to the arithmetic operators, Java provides a variety
of other operators. Some allow two values to be compared, and they
produce a boolean value (i.e. true or
false).
| Operator | Meaning |
|---|---|
== |
equality operator returns true if
and only if its operands are equal. |
!= |
inequality operator returns true
if and only if its operands are different. |
< |
less than operator returns true
if and only if its left operand is less-than its right
operand. |
> |
greater than operator returns
true if and only if its left operand is greater-than
its right operand. |
<= |
less than or equal to operator returns
true if and only if its left operand is not greater
than its right operand. |
>= |
greater than or equal to operator returns
true if and only if its left operand is not less than
its right operand. |
In Java, a true/false value is represented by the
Boolean type, denoted boolean. Most
Boolean operators describe the relationship between two values, so
they are often called relational operators.
The boolean type has two literals:
true and false.
Do this...
Create a test method in Experiment04Test named
testRelationalOperators(). Add these assertions to the
new test method, substituting in an appropriate comment or value
for each ???:
assertEquals("5 is equal to ???", true, 5 == ???);
assertEquals("5 is not equal to ???", false, 5 == ???);
assertEquals("5 is not-equal to ???", true, 5 != ???);
assertEquals("5 is not not-equals to ???", false, 5 != ???);
assertEquals("5 is less than ???", true, 5 < ???);
assertEquals("5 is not less than ???", false, 5 < ???);
assertEquals("5 is ??? 6", ???, 5 <= 6);
assertEquals("5 is ??? 3", ???, 5 <= 3);
assertEquals("5 is greater than ???", true, 5 > ???);
assertEquals("5 is not greater than ???", false, 5 > ???);
assertEquals("5 is ??? 6", ???, 5 >= 6);
assertEquals("5 is ??? 3", ???, 5 >= 3);
These particular assertions compare integers, but the comparison
operator can be used with any numeric type, integer or
floating-point. There is one case to be concerned about:
floating-point equality. Due the way that floating-point numbers
are computed, they aren't perfectly accurate, so instead of testing
x==3.14159, you test a small range around the value.
This is why assertEquals() requires three values:
assertEquals(3.14159, x, 1e-8);
The 1e-8 is a really small number which
indicates how closely (in this case) x should be to
3.14159. For most of the things that we'll do, using the value
1e-8 should be good enough, but depending on the
problem, this value might have to be change to make the test easier
or harder.
Actually, we've done things wrong, above. We really shouldn't
test with boolean literals since JUnit provides a
better way of stating the test. Instead of writing these
statements:
assertEquals("5 is equal to ???", true, 5 == ???);
assertEquals("5 is not equal to ???", false, 5 == ???);
We should write these:
assertTrue("5 is equal to ???", 5 == ???);
assertFalse("5 is not equal to ???", 5 == ???);
However, for this experiment it was more important to try out
the true and false literals. In the rest
of the experiments we'll use these alternatives, but there's no
need to change the tests for this experiment.
boolean, Boolean type, equality operator, greater than operator, greater than or equal to operator, inequality operator, less than operator, less than or equal to operator, relational operator