Exercise: Operators And Assignments

Questions for: Operators And Assignments

Which two are equal?
  1. 32/4
  2. (8 >> 2) << 4
  3. 2^5
  4. 128 >>> 2
  5. 2 >> 5
A:
1 and 2
B:
2 and 4
C:
1 and 3
D:
2 and 3
Answer: B

(2) and (4) are correct. (2) and (4) both evaluate to 32. (2) is shifting bits right then left using the signed bit shifters >> and <<. (4) is shifting bits using the unsigned operator >>>, but since the beginning number is positive the sign is maintained.

(1) evaluates to 8, (3) looks like 2 to the 5th power, but ^ is the Exclusive OR operator so (3) evaluates to 7. (5) evaluates to 0 (2 >> 5 is not 2 to the 5th).

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import java.awt.Button;
class CompareReference 
{
    public static void main(String [] args) 
    {
        float f = 42.0f;
        float [] f1 = new float[2];
        float [] f2 = new float[2];
        float [] f3 = f1;
        long x = 42;
        f1[0] = 42.0f;
    }
}
which three statements are true?
  1. f1 == f2
  2. f1 == f3
  3. f2 == f1[1]
  4. x == f1[0]
  5. f == f1[0]
A:
1, 2 and 3
B:
2, 4 and 5
C:
3, 4 and 5
D:
1, 4 and 5
Answer: B

(2) is correct because the reference variables f1 and f3 refer to the same array object.

(4) is correct because it is legal to compare integer and floating-point types.

(5) is correct because it is legal to compare a variable with an array element.

(3) is incorrect because f2 is an array object and f1[1] is an array element.

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Which two statements are equivalent?
  1. 3/2
  2. 3<2
  3. 3*4
  4. 3<<2
A:
1 and 2
B:
2 and 3
C:
3 and 4
D:
1 and 4
Answer: C

(1) is wrong. 3/2 = 1 (integer arithmetic).

(2) is wrong. 3 < 2 = false.

(3) is correct. 3 * 4 = 12.

(4) is correct. 3 <<2= 12. In binary 3 is 11, now shift the bits two places to the left and we get 1100 which is 12 in binary (3*2*2).

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Which two statements are equivalent?
  1. 16*4
  2. 16>>2
  3. 16/2^2
  4. 16>>>2
A:
1 and 2
B:
2 and 4
C:
3 and 4
D:
1 and 3
Answer: B

(2) is correct. 16 >> 2 = 4

(4) is correct. 16 >>> 2 = 4

(1) is wrong. 16 * 4 = 64

(3) is wrong. 16/2 ^ 2 = 10

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Which of the following are legal lines of code?
  1. int w = (int)888.8;
  2. byte x = (byte)1000L;
  3. long y = (byte)100;
  4. byte z = (byte)100L;
A:
1 and 2
B:
2 and 3
C:
3 and 4
D:
All statements are correct.
Answer: D

Statements (1), (2), (3), and (4) are correct. (1) is correct because when a floating-point number (a double in this case) is cast to an int, it simply loses the digits after the decimal.

(2) and (4) are correct because a long can be cast into a byte. If the long is over 127, it loses its most significant (leftmost) bits.

(3) actually works, even though a cast is not necessary, because a long can store a byte.

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