Understanding how this code works..

[Viv Richard]

From my book(HeadFirst Java), I was doing an exercise. This exercise was about putting together few pieces of codes which were already provided and also coming up with the provided output. I did the putting together part(which I think is the easiest part, it compiles and gives the required output as well). But I'm having hard time understanding the logic. Here below is the code and expected output:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
class CodeMagnets
{

public static void main (String[] args){

int z = 3;

if (z >2)
{
System.out.print("a");
}


while (z >0)
{
z = z - 1;
System.out.print("-");



if (z == 1)
{
System.out.print("d");
z = z - 1;

}
if (z == 2)
{
System.out.print("b c");
}





}//end of while
}//end of main
}//end of class

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Expected Output:

C:\>java CodeMagnets
a-b c-d

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Now my questions are mainly regarding those if statements. HOW or WHY making if statement with z, >, = and numeric value could put those letters in such orderly position?

I can READ the code as which line is doing what such as decrementing, initializing variables, if statement and so on. But I'm having hard time with logic. Help please.

[Kail Limas]

The Question you have to ask yourself is: When will the code be used? Under which condition is for example the first if clause used? It should be easy to see then.

[Jon Anslow]

Hi Viv,

 
if ( testCondition is true)
{
  //if statement is entered into
  //relevant code executed
}

your first if statment is using the > (greater than operator) and is checking "is current value of z variable greater than 2" z is currently 3 so it is true. Code in if statment will be executed.

 
while (testCondition is true)
{
    //enter while loop
    //execute code
}

The while loop will be executed until the test condition is false. Again, the condition here is using the > operator.

The other operator used in your code is == which is testing is z int value equal to another int value.

I hope these explanations help you look over your code, to understand the logic and what is happening.

Regards,
Jon

[Viv Richard]

Thanks a lot guys. The way I was not right way of thinking. That's why I was having hard time understanding.
I was thinking a-b c-d and 3,2,1,0 as their position in a string. So if my map had to be implemented, the position would have been 0 1 2 3. But the situation here is different abd I realized it. Thanks a lot. I will be back here and talk to you guys again.

Viv