Need help sorting out this movement function

Question

Hi guys just wondering if you could help me out, could you tell me what i am doing wrong here, what i am trying to do is add 1 if r is typed and subtract 1 if L is typed for both the lower and upper cases. but the position keeps returning the original. please help!!

    int position = 0;
    System.out.print("move: ");
    String car = Global.keyboard.nextLine();
    if (car == "r/")
        position =  + 1;
    if (car == "R")
        position = +1;
    if (car == "l")
        position =  -1;
    if (car == "L")
        position = -1;
        System.out.print(position);

http://stackoverflow.com/questions/767372/java-string-equals-versus — kiheru, Aug 27 '13 at 15:07
Most of the answers mention that `position = +1;` should be `position += 1;`, yet no-one mentioned the preferred way of `position++;`. — Bernhard Barker, Aug 27 '13 at 15:17
Also, what happens when you don't press `r`, `R`, `l` or `L`? Did you notice that you execute all of the `if`s regardless of which key was pressed? I've taken that into account, should you need another point of view. — Fritz, Aug 27 '13 at 15:28

codeMan · Accepted Answer · 2013-08-27T15:19:52.923

2

use:

int position = 0;
System.out.print("move: ");
String car = Global.keyboard.nextLine();
if (car.equals("r"))
    position += 1;
if (car.equals("R"))
    position += 1;
if (car.equals("l"))
    position -= 1;
if (car.equals("L"))
    position -= 1;
    System.out.print(position);

edited Aug 27 '13 at 15:19

answered Aug 27 '13 at 15:08

codeMan

5,730
3
27
51

`car` appears to be a `String`, not a `char`. As stated in the question: `String car = Global.keyboard.nextLine();` – Josh M Aug 27 '13 at 15:12
Still incorrect, he wants to create a running total (as specified in the question) but you are assigning the values of +/-1 depending on certain conditions. – Josh M Aug 27 '13 at 15:14
Can you please explain ur self, I dint understand last comment – codeMan Aug 27 '13 at 15:15
He wants to create a running total, re-read the question for further clarification. – Josh M Aug 27 '13 at 15:17
Yeah! just got that. Thanks :) – codeMan Aug 27 '13 at 15:20

score 0 · Answer 2 · answered Aug 27 '13 at 15:09

0

If you want a 1 liner, use this:

position += car.equalsIgnoreCase("r") ? 1 : car.equalsIgnoreCase("l") ? -1 : 0;

answered Aug 27 '13 at 15:09

Josh M

11,611
7
39
49

score 0 · Answer 3 · answered Aug 27 '13 at 15:10

0

use one of these styles :

position += 1
position -= 1

or

position = position + 1
position = position - 1

to add or subtract 1 from a value. Currently you're just assigning it the value + / - 1.

answered Aug 27 '13 at 15:10

Graham Griffiths

2,196
1
12
15

while in this case using `+=1` and `-=1` is better (because then changing the amount is easier), you really ought to at least mention that they could use `++` and `--` to accomplish this. – AJMansfield Aug 27 '13 at 15:22

Jakob · Answer 4 · 2013-08-29T15:30:56.357

0

Replace every car == "something" with car.equals("something")

Like this:

String car = Global.keyboard.nextLine();
if (car.equals("r"))
    position =  + 1;
if (car.equals("R"))
    position = +1;
if (car.equals("l"))
    position =  -1;
if (car.equals("L"))
    position = -1;
    System.out.print(position);

edited Aug 29 '13 at 15:30

answered Aug 27 '13 at 15:11

Jakob

751
4
17

I think you typo'd on `"r/"`. – AJMansfield Aug 27 '13 at 15:23

Fritz · Answer 5 · 2013-08-27T15:24:22.970

Instead of using multiple ifs (that should be if - else statements, so you don't cheack each one in every case) and Strings, remember that you can switch a char:

int position = 0;
//int dx = 1; For this case, the explanation is in a comment below.
System.out.print("move: ");
char car = Global.keyboard.nextChar();
switch(car) {
    case 'r':
    case 'R':
        position += 1; //Or position++ if you prefer, but I'd use this approach
                       //just in case you want to do position += 5 in the future
                       //or better yet, position += dx, being dx an int that
                       //defines the range of a single movement.
        break;
    case 'l':
    case 'L':
        position -= 1; //Same as with right, but position -= dx;
        break;
    default:
        System.out.println("Please, use r - R for (R)ight or l - L for (L)eft");
        break;
}
System.out.print(position);

Also, please note I changed your position updating. To adress your current question, == shouldn't be used to compare Strings since it compares references. Use equals instead.

Need help sorting out this movement function

5 Answers5