java - ArrayList 返回 null 的方法

Question

我希望此方法返回包含目录中所有文件名的字符串列表。我声明的列表从该方法返回为 null。有谁知道为什么？下面发布了代码片段。

   public static String docxList() {
        String path1 = "E:\\";
        String files = null;
        String display = null;
        String dpmt=null;

    //String variables declaration,
    try{
        Class.forName("oracle.jdbc.driver.OracleDriver");   
        java.sql.Connection 
        con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","user","pass");
        //Database connection Code
        PreparedStatement ps=con.prepareStatement("select * from EMP_DB where EMP_ID='EI-12'");
        ResultSet rs=ps.executeQuery();
        rs.next();
        dpmt=rs.getString("DEPARTMENT");

        path1 =path1+dpmt; //New path generation of specific directory according to user department

        File folder = new File(path1);
        File[] listOfFiles = folder.listFiles();
        for (int i = 0; i < listOfFiles.length; i++)
        {
            if (listOfFiles[i].isFile())
            {
                files = listOfFiles[i].getName();
                String filename=files;
                if(filename.indexOf(".")>0)
                {
                    filename=files.substring(0,files.lastIndexOf("."));
                }

                display=('<'+"A HREF"+'='+"\""+"PDFs/"+dpmt+"/"+files+"\""+" "+"target"+'='+"\""+"targetiframe"+"\""+'>'+'<'+"font"+" size"+'='+"\"4\""+" color"+'='+"\"white\""+'>'+filename+"</font>"+"<"+"/A"+'>');
                //Hyper-linked list of files. 
                ArrayList<String> al=new ArrayList<String>();
                al.add(display);
                //Adding all file names in a directory to a Arraylist.      
            }
        }
    }
    catch(Exception ex) 
    {
        System.out.print("Exception: "+ex+" in Dpmt Method.");  
        //Exception Display if any.
    }                                   

    return al; //ArrayList doesn't generate list of files in the drectory.
}

Answer 1

您在 return 语句无法看到的范围内声明了数组列表。将以下语句放在 for 循环之前。

ArrayList<String> al = new ArrayList<String>();

所以，它看起来像这样-

File[] listOfFiles = folder.listFiles();
ArrayList<String> al = new ArrayList<String>();

for (int i = 0; i < listOfFiles.length; i++)

..其余代码..

编辑:

您还应该修改方法签名以返回列表，而不是字符串。

public static ArrayList<String> docxList()