Java Reference
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Exercise 3.8 What would happen if you replaced the && operator in the test with ││ so that
if((replacementValue >= 0) ││ (replacementValue < limit))
Exercise 3.9 Which of the following expressions return true ?
! (4 < 5)
! false
(2 > 2) ││ ((4 == 4) && (1 < 0))
(2 > 2) ││ (4 == 4) && (1 < 0)
(34 != 33) && ! false
After writing your answers on paper, open the Code Pad in BlueJ and try it out. Check your
Exercise 3.10 Write an expression using boolean variables a and b that evaluates to true
when a and b are either both true or both false .
Exercise 3.11 Write an expression using boolean variables a and b that evaluates to true
when only one of a and b is true , and that is false if a and b are both false or both true . (This is
also called an exclusive or .)
Exercise 3.12 Consider the expression ( a && b ). Write an equivalent expression (one that
evaluates to true at exactly the same values for a and b ) without using the && operator.
The next method, getDisplayValue , also returns the display's value, but in a different for-
mat. The reason is that we want to display the value as a two-digit string. That is, if the current
time is 3:05 a.m., we want the display to read 03:05 , and not 3:5 . To enable us to do this
easily, we have implemented the getDisplayValue method. This method returns the current
value as a string, and it adds a leading 0 if the value is less than 10. Here is the relevant section
of the code:
if(value < 10) {
return "0" + value;
}
else {
return "" + value;
}
Note that the zero ( "0" ) is written in double quotes. Thus, we have written the string 0, not the
integer number 0. Then the expression
"0" + value
“adds” a string and an integer (because the type of value is integer). The plus operator, there-
fore, represents string concatenation again, as seen in Section 2.9. Before continuing, we will
now look at string concatenation a little more closely.

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