Java 对具有重复元素的集合进行排序。如果重复，按出现顺序排序

Question

我有一个 Element 类型的 java 集合，想法是按升序对其进行排序。但是，重复的元素应按出现顺序排序。让我用一些代码更好地解释一下:

public class Sorting {
    // Element class
    public static class Element {
       int value;
       String position;
    }
    // Comparator class
    public static class ElementComparator implements Comparator<Element> {
       @Override
       public int compare(Element e1, Element e2) {
          if (e1.value != e2.value) return e1.value - e2.value;
          return 1; // Elements have same value, so with this condition
                    // am I guaranteeing that duplicated elements are
                    // sorted by order of appearance ?
                    // I have been testing with this approach and it has worked fine
                    // but I am not sure how the sort could behave
                    // for other scenarios, eg, multithread environment
                    // I would like to know if this is a safe approach
       }
       @Override
        public String toString() {
            return "Element{" + "number=" + number + ", position=" + position + '}';
        }
    }
    // Main
    public static void main(String[] args) {
        List<Element> elements = new LinkedList<>();
        elements.add(new Element(3, "first 3"));
        elements.add(new Element(2, "first 2"));
        elements.add(new Element(2, "second 2"));
        elements.add(new Element(1, "first 1"));
        elements.add(new Element(1, "second 1"));
        elements.sort(new ElementComparator());
        for (Element e : elements) {
            System.out.println(e);
        }
        // It will print:
        // Element{number=1, position=first 1}
        // Element{number=1, position=second 1}
        // Element{number=2, position=first 2}
        // Element{number=2, position=second 2}
        // Element{number=3, position=first 3}
        // Notice that duplicated elements are sorted by order of appearance
    }
}

如果这种方法不安全，我正在考虑创建一个 Wrapper 类来进行排序。这个包装类类似于:

public class ElementWrapperForSorting {
   int value;
   String position;
   int positionOfAppearence;
}

这样，如果元素之间的值相同，我可以考虑字段 positionOfAppearence。

Answer 1

你不需要包装器。 List.sort是稳定的，所以相等的元素不会被重新排序。见 javadoc .