Java : 以相反的顺序从 List<String> 中加入字符串

Question

我有List<String> list = Arrays.asList("A", "B", "C");
我想用分隔符 , 以相反的顺序加入列表中的所有字符串：

//result
String joinedString = "C,B,A";

实现此目标的最佳方法是什么？
目前我使用索引循环：

String joinedString = "";
List<String> list = Arrays.asList("A", "B", "C");
for (int i = list.size() - 1; i >= 0; i--) {
     String string = list.get(i);
     joinedString = joinedString + string + ",";
}
//to remove ',' from the last string
if(joinedString.length() > 0) {
    joinedString = joinedString.substring(0, joinedString.length() - 1);
}

//Output    
C,B,A

Answer 1

最简单的就是使用Collections#reverse and String#join.

List<String> list = Arrays.asList("A", "B", "C");
Collections.reverse(list);
String joinedString = String.join(",", list);

Answer 2

另一种方式，使用比较器。

List<String> list = Arrays.asList("A", "B", "C");
list.sort(Comparator.reverseOrder());
String joinedString = String.join(",", list);

Answer 3

如果您不想通过调用 Collections.reverse(List<?> list) 来修改列表，请反向迭代列表。

如果您不知道列表类型，请使用 ListIterator 向后迭代列表而不损失性能，例如在 LinkedList 上的正常 i = 0; i < size() 循环否则会表现不佳。

要连接以逗号分隔的值，请使用 StringJoiner (Java 8+)。

List<String> list = Arrays.asList("A", "B", "C");

StringJoiner joiner = new StringJoiner(",");
for (ListIterator<String> iter = list.listIterator(list.size()); iter.hasPrevious(); )
    joiner.add(iter.previous());
String result = joiner.toString();

System.out.println(result); // print: C,B,A

Answer 4

使用供应商

List<String> list = Arrays.asList("A", "B", "C");
int i[] = { list.size() };
Supplier<String> supplier = () -> (i[0] > 0) ? list.get(--i[0]) : null;
String s, reverse = "";
while ((s = supplier.get()) != null) {
        reverse +=","+s;
}
reverse = (reverse.length() > 0) ? reverse = reverse.substring(1): "" ;

或代替 while 循环

reverse = list.stream().map(l->supplier.get()).collect(Collectors.joining(","));

Answer 5

一种方法使用StringBuilder

    StringBuilder sb = new StringBuilder();
    List<String> strs = Arrays.asList("A", "b", "c","d");
    for (int i = 0; i < strs.size(); i++) {
        sb.append(strs.get(i));
        if (i != strs.size() - 1) {
            sb.append(",");
        }
    }
    System.out.println(sb.reverse().toString());

Answer 6

这是使用 Java 8 的一种解决方案：

Collections.reverse(list);

//res contains the desired string
String res = list.stream().collect(Collectors.joining(","));

Answer 7

它可能是有用的类连接收集器：

    public static Collector<CharSequence, ?, String> joiningReversed(CharSequence delimiter, CharSequence prefix, CharSequence suffix) {
    return Collector.of(StringBuilder::new,
            (sb, item) -> {
                if (sb.length() != 0) {
                    sb.insert(0, delimiter);
                }
                sb.insert(0, item);
            },
            (a, b) -> {
                throw new UnsupportedOperationException();
            },
            sb -> sb.insert(0, prefix).append(suffix).toString());
    }

并在流中使用它：

    List<String> list = Arrays.asList("A", "B", "C");
    String result = list.stream()
                .collect(joiningReversed(",", "", ""));
    System.out.println(result);

Java : 以相反的顺序从 List<String> 中加入字符串

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