Question

I am having problem with compilation that I don't understand and would appreciate some help. Excerpt from the code, other methods are omitted for brevity:

public class TableBuilder {
  List<String[]> rows = new LinkedList<String[]>();

  public void sortByColumn(final int colIndex) {
    int maxIdx = 0;
    for (String[] s : rows) maxIdx = Math.max(maxIdx, s.length - 1);
    if (colIndex < 0 || colIndex >= maxIdx) return

    Collections.sort(rows, new Comparator<String[]>() {
        @Override
        public int compare(String[] strings, String[] otherStrings) {
            return strings[colIndex].compareTo(otherStrings[colIndex]);
        }
    });
  }

}

Error that I receive is:

cannot return a value from method whose result type is void
                Collections.sort(rows ,new Comparator<String[]>() {
                                ^

When I change method signature to public int sortByColumn(final int colIndex) then I am getting error:

incompatible types
found   : void
required: int
                Collections.sort(rows, new Comparator<String[]>() {
                                ^

Why this code doesn't compile and how is return in anonymous Comparator class related to sortByColumn signature? Is it possibly compiler bug or what do I do wrong? Using javac 1.6.0_45.

Answer 1

您的比较者很好。问题是您尝试$('.fc-today-button').click(function () { $('#calendar').fullCalendar('gotoDate', currentDate); }); return的结果Comparator#sort。void。只要丢失return语句就可以了：

if (colIndex > 0 && colIndex <= maxIdx) {
    Collections.sort(rows, new Comparator<String[]>() {
        @Override
        public int compare(String[] strings, String[] otherStrings) {
            return strings[colIndex].compareTo(otherStrings[colIndex]);
        }
    });
}

Answer 2

我建议删除return语句，以便代码编译：

public class TableBuilder {
    List<String[]> rows = new LinkedList<String[]>();

    public void sortByColumn(final int colIndex) {
        int maxIdx = 0;
        for (String[] s : rows) maxIdx = Math.max(maxIdx, s.length - 1);
        if (colIndex < 0 || colIndex >= maxIdx) {
            Collections.sort(rows, new Comparator<String[]>() {
                @Override
                public int compare(String[] strings, String[] otherStrings) {
                    return strings[colIndex].compareTo(otherStrings[colIndex]);
                }
            });
        }
    }
}

Collections.sort方法会将rows集合排序为可变对象。它不会将已排序的集合作为新对象返回。

Answer 3

这是由BackSlash

突出显示的拼写错误

Collections.sort with Comparator<string[]> compile error

3 个答案: