How to get rid of ", " in the end of my print?

Question

So I created a toString method that changes my stack into a string type. I want my output to be [A, B, C] but in my method it returns an extra ", " in the end which I do not want it to do. How do I make it so that my method does not put the comma space after the last element.

Here's my code:

public String toString(){

    StringBuilder sb = new StringBuilder("[");
    Node<E> temp = topOfStack;
    while (temp != null) {
        sb.append(temp.data).append(", ");
        temp = temp.next;
    }
    return sb.append("]").toString();

}

Here's my test:

public void testToString() {

    assertEquals("[A, B, C]", stack.toString());

}

Here's the output on my toString method:

[A, B, C, ]

Answer 1

Actually there can be many more way to do that .. following is just one of them.

while (temp != null) {
        sb.append(temp.data);
        temp = temp.next;
        if(temp != null)
           sb.append(",");
    }

Answer 2

This is a good logic exercise so I'll just give hints. Instead of unconditionally adding the comma, you only want to add it in certain cases. For example:

A           //No comma since string was empty before adding A
A, B        //Hint: the comma is coming before the B!
A, B, C     //Same hint

So you only want to include the comma if the string you're adding to is not empty (as is the case when you add the B and C, but not A). How can you program that?

And yes, I'm deliberately leaving the [ ] characters out; implement the logic I specified above first, and then it's trivial to put the brackets in.

Answer 3

Try this sb.substring(0,sb.length()-1);

Answer 4

A simple trick I like in these cases is to check if string builder is not empty and prepend delimeter. Pseudocode:

StringBuilder sb = new StringBuilder();
while(foo.hasNext()) {
    if (sb.length() > 0) sb.append(", ");

    sb.append(foo.bar()); 
}

Answer 5

You could try changing your return statement to something like this:

ln = sb.length();
return sb.substring(0,ln-1).append("]").toString();

Answer 6

Just updated your method:

public String toString(){

StringBuilder sb = new StringBuilder("[");
Node<E> temp = topOfStack;
while (temp != null) {
    if(sb.length() > 1)
       sb.append(", ");
    sb.append(temp.data);
    temp = temp.next;
}
return sb.append("]").toString();

}

Cheers !!

Answer 7

Try this :)

 public String toString(){

    StringBuilder sb = new StringBuilder("[");
    Node<E> temp = topOfStack;
    while (temp != null) {    
    sb.append(temp.data).append(temp.next == null ? "" : ", "); 
    temp = temp.next;
    }
    return sb.append("]").toString();

}