import java.io.File;
class  Demo
{
public static void main(String[] args) 
{
String realPath = "C:\\HQ\\1.png";
int a = realPath.lastIndexOf("\\");
String folderPath = realPath.substring(0,a);
System.out.println(folderPath);
File file = new File(folderPath);
String dirPath = file.getAbsolutePath();//目錄路徑
System.out.println(dirPath);
if (file.isDirectory())
{
File [] files = file.listFiles();//獲取此目錄下的檔案列表
int num=0;//加迴圈變數
for (File fileFrom :files )
{
String fromFile = fileFrom.getName();//得到單個檔名
System.out.println(fromFile);
if (fromFile.endsWith(".jpg"))
{
fromFile = fromFile.substring(0,fromFile.lastIndexOf("."));
System.out.println(fromFile);
String toFileName = dirPath+ "\\"+fromFile+num+".jpg";//這一行可以新增想要命名的變數
System.out.println(toFileName);
File toFile = new File(toFileName);
System.out.println(toFile);


if (fileFrom.exists()&&!toFile.exists())
{
//開始命名
fileFrom.renameTo(toFile);
}
}


num=num+1;
}
}
}

}

//遇到某行程式碼不理解輸出為啥，可以嘗試下System.out.println(xxx)