Chap 4 - Operators

Question 1

int a = 1
int b = ++a
int c = a++

System.out.println(“a = “ + a);
System.out.println(“b = “ + b);
System.out.println(“c = “ + c);

Answer 1

a = 3
b = 2
c = 2

c sets to a before it’s incremented

Question 2

What does % operator do?

Called modulus operator

Answer 2

Returns the remainder of a division operation

Question 3

What is Twos Compliment?

Answer 3

Encoding for negative numbers

Question 4

For binary code, change 42 to -42.

Answer 4

00101010 = 42
11010110 = -42

Question 5

List steps for changing number to its negative in binary

Answer 5

1) invert (0s to 1s and visa versa)
2) add 1

Question 6

Which bit tells you the sign of an integer?

Answer 6

highest order bit, on the left

Question 7

Bitwise operators, explain

&
|
~

Answer 7

AND, OR, NOT

AND says if both are 1
OR says if either are 1
NOT inverts the 1<>0

Question 8

Write the bitwise OR operator

Answer 8

|

00101010
| 00001111
—————
00101111

Question 9

What is bitwise XOR operator and what does it do?

Answer 9

Says if exactly one is 1/TRUE

00101010
^ 00001111
—————
00100101

Question 10

What does left shift operator &laquo_space;do?

Answer 10

shifts all bits in a value to the left a specified number of times

value &laquo_space;num

Question 11

Bye and short values are promoted to what when an expression is evaluated?

Answer 11

int

Question 12

Each &laquo_space;has the effect of what on the original value?

Answer 12

Doubling, except when a 1 gets shifted off the right, then its a problem

Question 13

byte a = 64, b;
int i;

i = a &laquo_space;2;
b = (byte) (a &laquo_space;2);

// print i and b

Answer 13

i = 256
b = 0

–
0100 0000 is 64. Shift left 2 is
1 0000 0000

That number is 256 as an int
Buts its 0 as a byte b/c the leftmost 1 is shifted out / too many numbers for the variable size

Question 14

Explain what happens with&raquo_space; operator, how the top bit is filled, and what the outcome is

Answer 14

Bitwise operator that shifts each bit to the right.
Top bit is filled with the previous content of the top bit
Outcome divides value by two and discards remainder

Question 15

What does&raquo_space;> do?

Answer 15

unsigned shift-right operator

Shifts bits to the right and 0 into the top bit, unlike&raquo_space; which maintains the sign for the top bit

Question 16

Bitwise operator compound assignments

int a = 1, b=2, c=3;

a |= 4;
b&raquo_space;= 1;
c «= 1;
a ^= c;

// print a b c

Answer 16

a = 3
b = 1
c = 6

Question 17

int a = 4, b =1;
boolean c = a < b;

// print c

Answer 17

FALSE

Question 18

What are short-circuit logical operators? And why use it?

e.g. || &&

Answer 18

For boolean values, these will stop evaluating the expression if the outcome can be determined by the left operand alone

Use it to avoid errors like, if denominator is not zero.
if (denom != 0 && num / denom > 10)

// if denom was zero, would cut out so dont get runtime error dividing by 0

Question 19

Explain how the ? operator works

Answer 19

It’s a three-way operator like the IF function in excel. If a condition is true, return first, if not return second.

int i, k;
i = 10;

k = i < 0 ? -i : i;
//prints i = 10

i = -10;
k = i < 0 ? -i : i;
//prints -i = 10

Question 20

What is a relational operator versus a logical operator?

Answer 20

Relational evaluate relationship between two objects

Logical calculate a boolean value between boolean objects

Question 21

In binary operations, order of evaluation is from ____ to ____ except for assignments which are ____ to ____

Left / Right?

Answer 21

Left to right except for assignments which go right to left