java - Guava Joiner在空元素上抛出NPE

Joiner的初始化在这里不正确吗？我有以下课程，当我尝试将示例paths数组与joiner结合在一起时，我得到了NullPointerException。

public class CPath {
  private static final Joiner joiner = Joiner.on("/");

  private String[] elements;

  @Override
  public String toString() {
    return joiner.join(elements);
  }
}

// main method
final String[] paths = {"a/b/c", "d", "", null, "e/f/g", "h/i", null, ""};
final CPath c3 = new CPath(paths);
c3.toString(); //<<<< NPE

最佳答案

您必须使用skipNulls()或useForNull(defaultValue)，它位于其文档的顶部；


  如果未指定skipNulls（）和useForNull（String），则任何给定元素为null时，联接方法都将引发NullPointerException。


因此，您必须像这样初始化joiner；

Joiner joiner = Joiner.on("/").skipNulls();

要么

Joiner joiner = Joiner.on("/").useForNull("");

Documentation of Joiner from Guava