ArrayList不在Java中添加userinput

Question

The purpose of this program is to print out a message saying 'you missed' each time a coordinate is entered.However,if a duplicate coordinate is entered,it should say 'This coordinate is already present.'

I used 2 arraylists simultaneously,to independantly store the values of x and yI fail to understand what is wrong with my code.The if statements don't seem to be working at all and the userinput also doesnt seem to be added to the arraylists.

Scanner a=new Scanner(System.in);

//Arraylist stores all entered x values.
ArrayList<Integer> XValues=new ArrayList<Integer>();
//Arraylist stores all entered y values.
ArrayList<Integer> YValues=new ArrayList<Integer>();

int Nooftries=0;
int xcoord;
int ycoord;

for(int i=0;i<10;i++)
{
    Nooftries++;
    System.out.println("This is guess #"+Nooftries);

    System.out.print("Please input your x location (0-3) : ");
    xcoord=a.nextInt();
    System.out.print("Please input your y location (0-3) : ");
    ycoord=a.nextInt();

    XValues.add(xcoord);
    YValues.add(ycoord);


    for(int c=0;c<XValues.size();c++)
    {

        if(xcoord==XValues.get(c) && ycoord==YValues.get(c))
        {

            System.out.println("You've already picked that spot.\n");
            break;
        }
        else
        {
            System.out.println("You missed!");
        }
    }
}

Answer 1

You do this:

XValues.add(xcoord);
YValues.add(ycoord);

And then you check. Since you've added the most recently input values, of course your arrays will contain those values when you check afterwards.

You'll want to check before adding. Alternatively you could just check up to XValues.size() - 1 , but doing the check before adding more clearly reflects your intent.

The if statements are working; your program is simply doing precisely what you told it to do. You just need to tell it to do the right thing!

The rest of your logic looks fine at a glance.

Answer 2

You have added xcoord and ycoord into the array lists right before the for loop, so of course the for loop will spot them and show You've already picked that spot . You should add them after the for loop.