if's

[George Willis]

I don't understand why somehow during my 4th If statement that my Boolean 'up' gets changed to False. I don't understand if 'up' is now changed to False that 'i' does not decrement. I figure that if the If does not satisfy the condition it should simply be skipped. But that does not seem to be the case.

public class Loop1 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int i = 0;
		boolean up = true;		
		
		for ( int n = 0; n < 100; n++){
			System.out.println(" Value of i = " + i);
			System.out.println(" Value of up-1 = " + up);//up1
			
			if (i > 600) {//if#1
				up = false;
				System.out.println("'up' changed to FALSE");
			} 
			
			System.out.println(" Value of up-2 = " + up);//up2
			if (i < -600) {//if#2
				up = true;
				System.out.println("'up' changed to TRUE");
			}
			
			System.out.println(" Value of up-3 = " + up);//up3
			if (up = true) {//if#3
				System.out.println("TRUE CONDITION");
				i++;
			} 
			
			System.out.println(" Value of up-4 = " + up);//up4
			if (up = false){//if#4
				System.out.println("FALSE CONDITION");
				i--;
			}
				
			System.out.println(" Value of up-5 = " + up);//up5
			
		}

	}

}

CONSOLE RESULTS:
Value of i = 0
Value of up-1 = true
Value of up-2 = true
Value of up-3 = true
TRUE CONDITION
Value of up-4 = true
Value of up-5 = false
Value of i = 1
Value of up-1 = false
Value of up-2 = false
Value of up-3 = false
TRUE CONDITION
Value of up-4 = true
Value of up-5 = false
Value of i = 2
Value of up-1 = false
Value of up-2 = false
Value of up-3 = false
TRUE CONDITION
Value of up-4 = true
Value of up-5 = false
Value of i = 3
...etcetera....

Thanks

[Jeanne Boyarsky]

This is something that is tricky for those new to Java

 if (up = true) 

This assigns true to up and checks if up is true. Which it always is.

 if (up == true) 

This checks if up is true.

You want the second one.

[George Willis]

Grrrr! I knew that but noobed it nonetheless.
Thanks!

[Paul Ngom]

Hi George,
What do you mean by 'noobed'?

[Matthew Brown]

That's one reason why I think it's preferable to use if(up) and if(!up), instead of if(up == true) and if(up == false).

[Campbell Ritchie]

Never try writing == false or == true.
Always write if (up)... or if (!up)...
That should prevent that particular error.

[Jeanne Boyarsky]

Paul Ngom wrote:Hi George,
What do you mean by 'noobed'?

noob is slang for someone new to something. It is a synonym for newbie.

Noobed is not something I had heard before, but I can infer it to mean to make a mistake that a new person would make.

[Scott Winterbourne]

Campbell Ritchie wrote:Never try writing == false or == true.
Always write if (up)... or if (!up)...
That should prevent that particular error.

This is something I need to keep in mind for myself also. I tend to write == true or == false.

[Paul Ngom]

noob is slang for someone new to something. It is a synonym for newbie.

Noobed is not something I had heard before, but I can infer it to mean to make a mistake that a new person would make.

Thank you Jeanne. I now get the meaning.

[Campbell Ritchie]

In which case it would be best to avoid noob as a verb in future, please. One reason for requiring real words is that they cause confusion to non‑native English speakers.

[George Willis]

Sorry for the rules mistake.
And, thank you all for the further discussion and advice.