About Question enthuware.ocajp.i.v7.2.916 :

[ETS User]

Good day. In this question also may create for loop.
for(;!isDone();){}

[admin]

That's a good point. Seems like a hack but works.

[Guest]

In the code from the question, the contents of the loop will always be run at least once before checking "isDone()" at the end. If we replace the original loop with "for(;!isDone();){}" we're not guaranteed to run the loop at least once, because the question says nothing about what "isDone()" actually does. For all we know it might return true even before reaching the loop. So not only does it look sort of look like a hack, but it might not give the same result either.

[Sweetpin2]

This question seems to have two answers as both of below code will work & is more readable. I don't know why do..while is only correct here.


for(;!isDone();) {//additional valid code}

do{//additional valid code}while( !isDone() );

[Sweetpin2]

Below is a sample code to justify my answer

public class For_Test {


static int i = 0;

public static void main(String[] args) {

for(;!isDone();)
{
System.out.println("Hello");
}

do
{
System.out.println("Hello World");

}while(!isDone());


}

static boolean isDone()
{
i++;
if(i==1) return false;
else return true;
}

}

[Guest]

Now I can't remember the question exactly, but the question doesn't say anything about isDone() does it? This means that when you use a for-loop, you're not guaranteed to the run code within the brackets, while using the do-while-loop, you're guaranteed to run the code at least once?

[Jokumo♫]

The explanation for the for-loop is wrong. In case you choose to use a for-loop instead of a do-while-loop you would have to code it like this:

Code: Select all

for(;true;){
    //additional valid code
    if(isDone()) break;
}

...a for-loop without initialization block and update statement acts just the same as a while-loop.

The question now is: Is a while-loop the same as a do-while-loop?

[zhengye1]

The explanation for the for-loop is wrong. In case you choose to use a for-loop instead of a do-while-loop you would have to code it like this:

Code: Select all

for(;true;){
    //additional valid code
    if(isDone()) break;
}

...a for-loop without initialization block and update statement acts just the same as a while-loop.

The question now is: Is a while-loop the same as a do-while-loop?

The difference for while-loop and do-while-loop is:
For while-loop, it will check the condition first, if condition matches, then execute the code that inside the while block.

For do-while-loop, it will always run at least once, then check the condition to check does the block of code need to run again or not

[edcrader]

The explanation for the for-loop is wrong. In case you choose to use a for-loop instead of a do-while-loop you would have to code it like this:

Code: Select all

for(;true;){
    //additional valid code
    if(isDone()) break;
}

...a for-loop without initialization block and update statement acts just the same as a while-loop.

The question now is: Is a while-loop the same as a do-while-loop?

The difference for while-loop and do-while-loop is:
For while-loop, it will check the condition first, if condition matches, then execute the code that inside the while block.

For do-while-loop, it will always run at least once, then check the condition to check does the block of code need to run again or not

Your absolutely right on the way the do-while and while loop work. However, in this case you have to pay close attention to the while(true). The condition is true and will always be true (causing an infinite loop). This means there is no chance the while loop won't run at least once.

Therefore, in this case the program functionality is similar even though functionality of the loops are different.

[dvc1190]

Below is a sample code to justify my answer

public class For_Test {


static int i = 0;

public static void main(String[] args) {

for(;!isDone();)
{
System.out.println("Hello");
}

do
{
System.out.println("Hello World");

}while(!isDone());


}

static boolean isDone()
{
i++;
if(i==1) return false;
else return true;
}

}

Your code example is written so that isDone will return true at least once. What if isDone always returned false? Or what if your first value was 1? Then the for loop would not behave the same as a do-while nor will it behave the same as the bad example we are trying to correct in the question.

[OCAJO1]

Just wondering what type of a code would have made "use a for loop" the correct answer?

[admin]

for is perfectly suitable when you need to have an iteration variable and you want to use it inside the loop. Something like this:

Code: Select all

for(int i=0; i<10; i++){
  array[i] = i*i; //using iteration variable to initialize all array elements 
}

[OCAJO1]

Actually I was more referring to the fact that the following explanation was given, but the answer itself was NOT chosen as the right one.

"The following is how it can be done using a for loop: for(;!isDone();) { //additional valid code }"

I wanted to find out what kind of code in the question, would have made the above answer, rather than the do-while, the correct answer?

Thanks

[admin]

If the objective is to improve readability, this code wouldn't ever be the correct answer even though it is a valid piece of code.