NullPointerException：尝试调用虚拟方法'；布尔值java.lang.String.equals（java.lang.Object）'；关于空对象引用

我在运行项目时遇到此错误

java.lang.NullPointerException:尝试调用虚拟方法 空对象上的“boolean java.lang.String.equals（java.lang.Object）” 参考 在com.example.arhen.tugasrplii.Register$InputData.onPostExecute（Register.java:100）上

这是完整日志：

03-05 03:22:02.822    2575-2575/com.example.arhen.tugasrplii E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.arhen.tugasrplii, PID: 2575
    **java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
            at com.example.arhen.tugasrplii.Register$InputData.onPostExecute(Register.java:100)**
            at com.example.arhen.tugasrplii.Register$InputData.onPostExecute(Register.java:54)
            at android.os.AsyncTask.finish(AsyncTask.java:632)
            at android.os.AsyncTask.access$600(AsyncTask.java:177)
            at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

这是我在Register.java上的完整代码：

/**  * Created by arhen on 05/03/15.  */ 
public class Register extends Activity{
    ProgressDialog pDialog;
    JSONParser jsonParser = new JSONParser();

    EditText first_name,last_name,email,username,password;

    private static String url = "http://127.0.0.1/login/register.php";

    Button register;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.register);

        register   = (Button)findViewById(R.id.btn_register);
        first_name = (EditText)findViewById(R.id.fld_first);
        last_name  = (EditText)findViewById(R.id.fld_last);
        email      = (EditText)findViewById(R.id.fld_email);
        username   = (EditText)findViewById(R.id.fld_username);
        password   = (EditText)findViewById(R.id.fld_pwd);

        register.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                new InputData().execute();
            }
        });
    }

    public class InputData extends AsyncTask<String, String, String>{
        String success;
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(Register.this);
            pDialog.setMessage("Registering Account...");
            pDialog.setIndeterminate(false);
            pDialog.show();
        }

        @Override
        protected String doInBackground(String... args) {

            String strfirst_name    = first_name.getText().toString();
            String strlast_name     = last_name.getText().toString();
            String stremail         = email.getText().toString();
            String strusername      = username.getText().toString();
            String strpassword      = password.getText().toString();

            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("first_name",strfirst_name));
            params.add(new BasicNameValuePair("last_name",strlast_name));
            params.add(new BasicNameValuePair("email",stremail));
            params.add(new BasicNameValuePair("username",strusername));
            params.add(new BasicNameValuePair("password",strpassword));

            JSONObject json =
                    jsonParser.makeHttpRequest(url,
                            "POST", params);
            try {
                success = json.getString("success");
            } catch (Exception e) {
                runOnUiThread(new Runnable() {
                    public void run() {
                        Toast.makeText(getApplicationContext(), "Error", Toast.LENGTH_SHORT).show();
                    }
                });
            }
            return null;
        }

        protected void onPostExecute(String file_url) {
            // dismiss the dialog once done
            pDialog.dismiss();
            if (success.equals("1")) {
                Toast.makeText(getApplicationContext(),"Registration Succesfully",Toast.LENGTH_LONG).show();
            }else{
                Toast.makeText(getApplicationContext(),"Registration Failed",Toast.LENGTH_LONG).show();
            }
        }
    }

    @Override
    public void onBackPressed(){
        Intent i = new Intent(getApplicationContext(),Login.class);
        i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(i);
        finish();
    } }

但是它不起作用。。它给出了在我的代码上激活的此语句错误：

runOnUiThread(new Runnable() {
                    public void run() {
                        Toast.makeText(getApplicationContext(), "Error", Toast.LENGTH_SHORT).show();
                    }
                });

我不知道。请帮忙。。

---

非常感谢…

如果

String success=“

不起作用，则此行可能返回null：

success = json.getString("success");

---

您是否检查了正在解析的JSON，并验证了“success”字段是您期望的位置，并且格式正确？

我认为与u类似。所以我检查了我的JSONParser.java代码。但看起来没问题。也许我遗漏了什么，你也可以检查一下。我将JSONParser.java和register.php代码放在上面，手动验证php中的JSON。用浏览器点击它并检查它是否正确。如果是这样的话，那么您的Java很可能会受到指责。另外，编写单元测试有助于避免类似的情况。谢谢。它的作品：）。

String success ="";

runOnUiThread(new Runnable() {
                    public void run() {
                        Toast.makeText(getApplicationContext(), "Error", Toast.LENGTH_SHORT).show();
                    }
                });

success = json.getString("success");