Multiple Choice Question

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Submitted by c-admin on Tue, 05/28/2019 - 06:18

QID:

152

Type:

Multiple Choice Question

Category:

Java Programmer I

Tags:

decision constructs

Question:

What is the result of executing the following fragment of code:

boolean b1 = false;
boolean b2 = false;
if (b2 != b1 = !b2){
System.out.println("true");
}else{
System.out.println("false");
}

Select 1 option

A. Compile time error.
B. It will print true.
C. It will print false.
D. Runtime error.
E. It will print nothing.

Answer and Explanation (Click to expand)

Answer:

Explanation:

Note that boolean operators have more precedence than =. (In fact, = has least precedence of all operators.) so, in (b2 != b1 = !b2) first b2 != b1 is evaluated which returns a value 'false'. So the expression becomes false = !b2. And this is illegal because false is a value and not a variable!

Had it been something like (b2 = b1 != b2) then it is valid because it will boil down to : b2 = false.

Because all an if() needs is a boolean, now b1 != b2 returns false which is a Boolean and as b2 = false is an expression and every expression has a return value (which is actually the Left Hand Side of the expression). Here, it returns false, which is again a boolean.

Note that return value of expression : i = 10 , where i is an int, is 10 (an int).

Q&A Set:

Set 14

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