Java 不一致的空指针异常
我正在尝试从设备外部目录读取.json文件 我有一个名为ExternalFile的类,用于读入文件并以字符串形式返回内容 下面是课堂:Java 不一致的空指针异常,java,android,json,Java,Android,Json,我正在尝试从设备外部目录读取.json文件 我有一个名为ExternalFile的类,用于读入文件并以字符串形式返回内容 下面是课堂: public class ExternalFile { final String EXTERNAL_STORAGE = Evironment.getExternalStorageDirectory().toString(); final String FIRSTDROID_DIRECTORY = EXTERNAL_STORAGE + "/firstdroid/"
public class ExternalFile
{
final String EXTERNAL_STORAGE = Evironment.getExternalStorageDirectory().toString();
final String FIRSTDROID_DIRECTORY = EXTERNAL_STORAGE + "/firstdroid/";
final String SALES_DIRECTORY = FIRSTDROID_DIRECTORY + "sales/";
final String REFERENCE_DIRECTORY = FIRSTDROID_DIRECTORY + "reference/";
public String readFile(String direcectory, String fileName)
{
BufferedReader br;
StringBuilder sBuffer;
File JSON;
String line;
String retVal = null;
try
{
sBuffer = new StringBuilder();
JSON = new File(direcectory, fileName);
br = new BufferedReader(new FileReader(JSON));
while ((line = br.readLine()) != null)
{
sBuffer.append(line);
sBuffer.append('\n');
}
retVal = sBuffer.toString();
Log.d("File Results: ", retVal);
}
catch (Exception e)
{
Log.e("readJSON", e.getMessage());
}
return retVal;
}
}
当我使用这个类读取“login.json”文件时,它工作得很好。但是,当我使用该类读取“contacts.json”文件时,eclipse警告:
“空指针访问:变量readJSON只能在此位置为空”
唯一的区别是我传入了“contacts.json”而不是“login.json”如果您使用变量而没有初始化它,Eclipse会发出警告。在代码中,声明了
readJSON
,但初始化为null
。在这之后,它被用于try
块中,这肯定会导致NPE
ExternalFile readJSON = null; //--> you have not intialized readJSON
try
{
result = readJSON.readFile(REFERENCE_DIRECTORY, "contacts.json");
^^^^^^^^
null access here
如果使用变量而未初始化它,Eclipse会发出警告。在代码中,声明了
readJSON
,但初始化为null
。在这之后,它被用于try
块中,这肯定会导致NPE
ExternalFile readJSON = null; //--> you have not intialized readJSON
try
{
result = readJSON.readFile(REFERENCE_DIRECTORY, "contacts.json");
^^^^^^^^
null access here