Enthuware

Explanation

1. i = (int) k.shortValue();   --> You can use *= here but then you can't complete the 4th line.
2. str += b; -->  You can't use =, or *= here. Only += is valid.
3. b = !b; --> You can't use anything other than = here.
4. c *= i; --> You can only use *= or +=. = is not valid. Further, if you use += here, you can't complete line 2.

But it compile
1. i *= (int) k.shortValue();
4. c *= i;

Yes, but if you use *= on 1st line, how will you complete the 4th?

will print '?'

You can't use *= more than once in this question.

I can use some explanation as to why you cannot assign a boolean to a String, but can do += (concatenate and assign). And also why we cannot assign an int to a char, but can do += (add and assign).

A String variable is a reference type and a boolean is a primitive, so, you cannot assign a boolean value to String variable. Thus, str = b; will not compile.

+= is a special operator in Java, which translates to concatenation and assignment. So, str += b becomes str = str + b;
Now, + operator is overloaded in Java. If one of the operands of + is a string, it converts the other operand into a string and concatenates the two string to produce a new string. In this case, b's value is converted to String. Therefore, it is ok to assign the string produced by str + b to be assigned back to str.

This is usually explained well in all certification books. Which book are you following? You may start with this book if you don't want to spend too much.

Hi.

Please, can someone enlighten me on why the item 4 works?

c *= i

afaik this is equivalent to:

c = c * i;

right?
And..an arithmetic operation should give a result at least as an int type. If so, "c * i" returns an int. How can that int be assigned to a char variable without casting?
What am I missing?

c *= i is not equivalent to c = c * i;
It is to equivalent c = (char)( c * i);

admin wrote: ↑

Mon May 02, 2022 1:13 am

c *= i is not equivalent to c = c * i;
It is to equivalent c = (char)( c * i);

ohh!
So compound assignments always have casts. I see

then... means Is that right?
Thank you!!

Correct. This is written in JLS Section 15.26.2 Compound Assignment Operators:

A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once.