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Thread: A touchy subject (good for beginners)

  1. #1
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    Default A touchy subject (good for beginners)

    This is oddly enough the reason I stopped using some other forum. Of course this was when I first started with java long ago. Well here is the subject first:

    A snippet from my infinite textbox code:

    do {
    g.drawString(content[iii],x+letterW*ii,y+letterH*i);
    ++ii;
    if(boundX < ii) {
    ii = 0; ++i;      }
    ++iii;
                   }while(iii < Array.getLength(content) || i > boundY);

    Now the thing that got me stuck - keep in mind this is not the exact example because in this case as simple && would suffice where as my original (can't remember that far back) would have been more specific - is this could easily give you a run-time error of ArrayIndexOutOfBounds. If I can just cut to the end ..

    The logic of the do while is:
    Call this option A)
    "continue while true"

    And it is not:
    we'll call this option B)

    "Break when false"

    Believe it or not this was the start of never ending debate. The simple fact is java at runtime analyzes conditions between the logical or operator individually for efficiency so java does this.

    while( something || somethingElse )

    it first say's is something true?

    CASE 1 something is not true

    A) continue to the next condition

    B) break

    CASE 2 something is true

    A) loop back up

    B) check the next condition



    I bring this up for two reasons, One, it is a good thing for new programmers to know it will help them avoid some serious mishaps, Two, I am kind of curious how you fellows take this.


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    Default Re: A touchy subject (good for beginners)

    I think you're saying that in a multi-condition conditional statement, Java only evaluates those conditions necessary to make a decision. I think a multi-AND situation demonstrates the idea more simply. In a multi-AND conditional statement, all conditions must be TRUE in order for the entire statement to be true. If any of the conditions are found false, the rest of the conditions are not evaluated. As an example:

    if ( case1 && case2 && case3 )

    If case1 is found to be false case2 and case3 are not evaluated.

    Is that your point? If so, what was the controversy (I don't really care, but you're welcome to vent if you'd like), and are you expecting some controversy now?

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    Super Moderator jps's Avatar
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    Default Re: A touchy subject (good for beginners)

    Quote Originally Posted by KAJLogic View Post
    Believe it or not this was the start of never ending debate.
    I do not see how this can be a debate, especially not a long one...
    Give values to the variables in a SSCCE: ~end of discussion, winner takes all.

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    Default Re: A touchy subject (good for beginners)

    Exclusive-and (&&) always short-circuit on the first condition found to be false (evaluation order is from left to right).

    Exclusive-or (||) always short-circuit on the first condition found to be true (evaluation order is again from left to right).

    public class Test
    {
    	public static boolean get(boolean val)
    	{
    	    System.out.println("get(" + val + ")");
    	    return val;
    	}
     
    	public static void main(String[] args)
    	{
    		System.out.println("res1");
    	    boolean res1 = get(false) && get(true);
    	    System.out.println("res2");
    	    boolean res2 = get(true) || get(false);
    	}
    }

    Output:

    res1
    get(false)
    res2
    get(true)
    This means code like this is perfectly safe:

    if(str != null && str.length() > 5)
    {
        // do something
    }

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    Default Re: A touchy subject (good for beginners)

    The guts of this post are that there is a BIG difference between break if false and continue while true. And, I was just curious if this was an infectious argument or something. The fact that there needs to be no debate is the reason I hope to be apart of this community for a long time. Honestly if a new comer asked me about the difference between the two I would say obviously it is not break when, because the statement is do WHILE. So to sum up the whole point is, there is very simple, there is a HUGE logical difference between continue while true is found or break when false is found. That is what they others refused to/couldn't understand, and the reason I lost trust in that forum (this was long ago).

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    Default Re: A touchy subject (good for beginners)

    I hope you can be happy here. You obviously have studied the details and like to share them.

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