For turning left or right you simply need a variable that tracks the direction, and then choose a value for that variable that represents the direction, for example the points of a compass North, East, South, West, or 0,1,2,3 where 0=North, 1=East, etc:
//Variable to track direction
public int direction = 0;
To turn simply update the variable, here is a turn left example:
public void turnLeft(){
if(direction == 0)
direction = 3;
else
direction = direction-1;
}
To track the car location simply use a Point variable:
Point location = new Point(0,0);
As for how to move forward, you simply adjust the loacation of your car based on the direction variable, we can do this easily with if statements:
public void moveForward(){
//North == 0
if(direction = 0)
location.y = location.y-1;
//East = 1
else if(direction == 1)
location.x = location.x+1;
//And so on...
}
And finally we store it in the array:
//show the new car location
pathArray[location.x][location.y] = 'X';
The complete code could go in it's own class a bit like this:
public class CarTracker{
//2d array to store path
char[][] pathArray = new char[10][10];
//Variable to track direction
//Start facine east (1)
int direction = 1;
//Track car location
Point location = new Point(0,0);
//Car symbol
char car = 'X';
char trail = 'O';
public void start(String commands, Point startLocation){
//read input commands
Scanner in = new Scanner(commands);
//Set start location
location = startLocation;
//Fill the array with blanks so that it prints nicely
for (int y = 0; y < pathArray.length; y++){
for (int x = 0; x < pathArray[y].length; x++)
pathArray[y][x] = ' ';
}
//Show the initial starting point for the print command
pathArray[location.y][location.x] = car;
//loop until exit
while(in.hasNext()){
String consoleInput = in.nextLine();
switch (consoleInput){
case "right":
turnRight();
break;
case "left":
turnLeft();
break;
case "exit":
System.exit(0);
break;
case "print":
print();
break;
case "forward":
moveForward();
break;
default:
System.out.println("Invalid command: "+consoleInput);
break;
}
}
}
public void turnLeft(){
if (direction == 0)
direction = 3;
else
direction = direction - 1;
}
public void turnRight(){
if (direction == 3)
direction = 0;
else
direction = direction + 1;
}
public void moveForward(){
//change previous character to a trail or mark the start
pathArray[location.y][location.x] = trail;
//North = 0
if(direction == 0)
location.y = location.y-1;
//East = 1
else if(direction == 1)
location.x = location.x+1;
//South = 2
else if(direction == 2)
location.y = location.y+1;
//West = 3
else
location.x = location.x-1;
//show the new car location
pathArray[location.y][location.x] = car;
}
public void print(){
System.out.println("Current Location:");
//loop the array and print
for (int y = 0; y < pathArray.length; y++){
for (int x = 0; x < pathArray[y].length; x++)
//Print each part of the grid
System.out.print("[" + pathArray[y][x] + "]");
//move to the next row
System.out.println();
}
}
}
Then using the following input from the main method (Where the car starts facing east in the above code):
CarTracker tracker = new CarTracker();
String commands =
"print\n" +
"forward\n" +
"forward\n" +
"right\n" +
"forward\n" +
"forward\n" +
"forward\n" +
"left\n" +
"forward\n" +
"forward\n" +
"left\n" +
"forward\n" +
"right\n" +
"forward\n" +
"print";
Point startLocation = new Point(0, 4);
tracker.start(commands, startLocation);
We get this output with the blank grid at the start, and the final printed grid shows the complete path and the final location:
Current Location:
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[X][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
Current Location:
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[O][O][O][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][O][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][O][ ][O][X][ ][ ][ ][ ]
[ ][ ][O][O][O][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
[ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
You will need to build in some error checking to make sure the car does not go outside the grid/array, and you will need to fix up a few other things like your input method, but it will get you started.
Edit: If you want to start outside the area for exampl elike this Point startLocation = new Point(-1, 0);, then remove the line that prints the start location:
//The initial starting point
//pathArray[location.y][location.x] = car;
And change the moveForward method to not modify the array if the start is outside the left side by adding this if check:
public void moveForward(){
//change previous character to a trail or mark the start
if(location.x >= 0){
pathArray[location.y][location.x] = trail;
}
