你要做的是：
1.遍历目录中的所有文件（您已经完成了）
1.检查它是否有一定的扩展名（它以一定的字符串结尾）
1.如果匹配，则打印文件名。

public class Main {

  // Here we have a constant containing the interesting file extensions
  public static final String[] extensions = new[] { ".txt", ".doc" };

  // This helper function will tell us whether 
  // a file has one of the interesting file extensions
  public static boolean matchesExtension(File file) {
    for(String ext : extensions) {
      if(file.getName().endsWith(ext)) { 
         return true; 
      }
    }
    return false;
  }

  public static void main(String[] args) {
        String folderpath = "G:\\AE_IntegrationComp";
        File directory = new File(folderpath);
        // Iterate through all files in the directory
        for(File file : directory.listFiles()){
            if(matchesExtension(file)){
                System.out.println(file.getName());
            }
        }

  }
}