Java列表可视化

Question

i've a List<Polygon> polygons , where Polygon represents the geojson concept of polygon. In the class Polygon i defined a method toGeojson() that returns a string containing the geojson representation. I'd like to print all the list in a compact way instead of doing this:

String result = '';
for(Polygon p: polygons)
   result += p.toGeojson();

I could do result = p.toString() but i cannot use toString() method because i use it for an other thing. Is there a way to call toGeojson() on a List just as you'd do with toString() ?

Answer 1

Not sure if that answers your question, but you can use Stream api for that thing.

String result = polygons.stream()
        .map(Polygon::toGeojson)
        .collect(Collectors.joining(","));

There is no direct way to override behaviour of List.toString() .

updated There is Collectors#joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix) method which accepts suffix and prefix. Using this method we can make our output look exactly like List.toSting with square brackets.

String result = polygons.stream()
            .map(Polygon::toGeojson)
            .collect(Collectors.joining(",", "[", "]")); // ["x","y"]

Answer 2

I am not sure I understand what you want, but I guess you are looking for a way to print the geoJson representation of each Polygon contained in your List. In that case I don't see a better way than a loop, but avoid String concatenation inside loops. Use StringBuilder instead which has much better performance .

StringBuilder result = new StringBuilder();
for (Polygon p: polygons) {
   result.append(p.toGeojson());
}

Answer 3

我认为，您的解决方案是最好的...在Java中，没有更快的解决方案，并且Array.toString方法的工作方式相同。