toString Override in Java

Question

This question is from an assignment. I have to override a toString() method in a class that creates a circularly linked list and I actually have a toString() method that works great, it passes all of my tests everything. So my project is autograded and it apparently doesn't approve of my method 100%. So my question is: is there a better way to write this toString() method that would be more efficient?

public String toString()
    {
        if (size == 0)
        {
            return "[]";
        }
        else
        {
            String output = "";
            Node<E> tempNode = actualElement;
            while (tempNode.next() != actualElement)
            {
                if (output.equals(""))
                {
                    output = "[" + output + tempNode.data().toString();
                    tempNode = tempNode.next();
                }
                else
                {
                    output = output + ", " + tempNode.data().toString();
                    tempNode = tempNode.next();
                }

            }
            output = output + ", " + tempNode.data().toString() + "]";
            return output;
        }

If i need to elaborate more on the class structure so that this makes more sense let me know.

Answer 1

Use StringBuilder.

StringBuilder builder = new StringBuilder();
builder.append("some text");
builder.append("more text");
return builder.toString();

Answer 2

To improve it further, you can use StringBuilder and append each computed String literals. This saves JVM creating load of individual String literals and thus improves performance.

Answer 3

Strings should always be used unless string builders offer an advantage in terms of simpler code or better performance

if you need to concatenate a large number of strings, appending to a StringBuilder object is more efficient.

Answer 4

I assume actualElement is defined elsewhere in the class, though a better name might be nice. The if (output.equals("")) is unnecessary. Just start the output StringBuilder with a [, and just append to it.

However, you are depending on your list actually being circular. If this list ends up not looping around, you will get an NPE. And, if the list looks more like a 6, as in [A, B, C, D, E, C, D, E...], then the loop will never end.

Answer 5

Use StringBuilder instead may do your a favor.This is snippet is copied from AbstractCollection.toString(),take a look at it.

 public String toString() {
    Iterator<E> i = iterator();
if (! i.hasNext())
    return "[]";

StringBuilder sb = new StringBuilder();
sb.append('[');
for (;;) {
    E e = i.next();
    sb.append(e == this ? "(this Collection)" : e);
    if (! i.hasNext())
    return sb.append(']').toString();
    sb.append(", ");
}
}

Answer 6

First you should use a StringBuilder for concatenation of your Strings.

take a look here:

http://javarevisited.blogspot.co.at/2011/07/string-vs-stringbuffer-vs-stringbuilder.html

StringBuilder sb = new StringBuidler();
Node<E> tempNode = actualElement;

while (tempNode.next() != actualElement)
{
    if (sb.length() == 0)
    {
        sb.append("[").append(tempNode.data().toString());
    }
    else
    {
        sb.append(", ").append(tempNode.data().toString());
    }
    tempNode = tempNode.next();
}
sb.append(", ").append(tempNode.data().toString()).append("]");
return sb.toString();