Java中String.join()高效字符串拼接的实现

String.join(CharSequence delimiter, CharSequence... elements)

String[] fruits = {"Apple", "Banana", "Cherry"};
String result = String.join(", ", fruits);
System.out.println(result); // 输出：Apple, Banana, Cherry

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
String result = String.join(" -> ", names);
System.out.println(result); // 输出：Alice -> Bob -> Charlie

String[] arr = {"A", "", "B"};
String result = String.join("-", arr); // 输出：A--B

.collect(Collectors.joining(delimiter, prefix, suffix))

List<String> list = Arrays.asList("One", "Two", "Three");
String result = list.stream()
    .collect(Collectors.joining(", ", "[", "]"));
System.out.println(result); // 输出：[One, Two, Three]

List<String> emptyList = Collections.emptyList();
String result = emptyList.stream()
    .collect(Collectors.joining(", ", "Items: [", "]"));
System.out.println(result); // 输出：Items: []（空集合时保留前缀和后缀）

Integer[] numbers = {1, 2, 3, 4, 5};
String result = Arrays.stream(numbers)
    .map(String::valueOf) // 转换为字符串
    .collect(Collectors.joining(" | "));
System.out.println(result); // 输出：1 | 2 | 3 | 4 | 5

StringBuilder sb = new StringBuilder();
for (String fruit : fruits) {
    if (sb.length() > 0) {
        sb.append(", "); // 手动添加分隔符
    }
    sb.append(fruit);
}
String result = sb.toString(); // 输出：Apple, Banana, Cherry

List<String> list = Arrays.asList("A", null, "B");
String result = list.stream()
    .filter(Objects::nonNull) // 过滤null
    .collect(Collectors.joining(", ")); // 输出：A, B

String result = String.join("", "Hello", "World"); // 输出：HelloWorld