当你示例化一个BuffereReader并将其赋值给count时，count将总是非空的，因此将满足while循环：

count = new BufferedReader(input); //count is holding an instance of BufferedReader.

while(count != null){ //here count is non-null and while loop is infinite and program never exits.

相反，使用以下代码，其中每行都将被读取并检查是否为空，如果为空，则程序将退出。

input = new FileReader(txt);
count = new BufferedReader(input);
String line = null;
while(( line = count.readLine())!= null){ //each line is read and assigned to the String line variable.
        System.out.println(line);
        result++;
 }

如果您使用的是JDK-1.8，则可以使用Files API来缩短代码：

int result = 0;
try (Stream<String> stream = Files.lines(Paths.get(txt.getAbsolutePath()))) {
      //either print the lines or take the count.
      //stream.forEach(System.out::println); 
      result = (int)stream.count(); 
} catch (IOException e) {
      e.printStackTrace();
}

count是你的BufferedReader，你的循环应该在line上！比如，

String line = "";
while (line != null) {
    line = count.readLine();

同样，你应该使用try-with-Resources来close你的资源（而不是finally块）。你可以更习惯地编写while循环。比如，

private int sizeOfFile(File txt) {
    int result = 0;
    try (BufferedReader count = new BufferedReader(new FileReader(txt))) {
        String line;
        while ((line = count.readLine()) != null) {
            System.out.println(line);
            result++;
        }
    } catch (FileNotFoundException ex) {
        ex.printStackTrace();
    } catch (IOException ex) {
        ex.printStackTrace();
    }
    return result;
}