E/AndroidRuntime（1253）：java.lang.NullPointerException

单击addSubject按钮时出错，导致应用程序崩溃。 我一直在寻找解决方案，似乎找不到有效的方法

任何帮助都将不胜感激

代码：

public class Setup extends Activity {
EditText subjectTextField;
dataBaseTools2 dbTools = new dataBaseTools2(this);
String BLANK = "";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_setup);

    final Button EditTextSubjectAdd = (Button) findViewById(R.id.buttonAddSub);
    EditTextSubjectAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            HashMap<String, String> querySubjectsMap = new HashMap<String, String>();

            subjectTextField = (EditText) findViewById(R.id.subjectField);
            querySubjectsMap.put("subject", subjectTextField.getText()
                    .toString());
            dbTools.insertSubject(querySubjectsMap);
            subjectTextField.setText(BLANK);
            // TODO Auto-generated method stub

        }

    });
    final Button finishButton = (Button) findViewById(R.id.finishButton);
    finishButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            finish();

        }

    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.setup, menu);
    return true;
}

---

任何帮助都将不胜感激

Place

subjectTextField=（EditText）findViewById（R.id.subjectField）。
什么是null？我愿意打赌subjectTextField为null，因为它未在该活动的布局中定义。onClick方法中的所有其他内容似乎都被正确实例化了，并且存储量丰富，问题得到了解决。
    11-18 16:50:27.263: E/AndroidRuntime(1410): FATAL EXCEPTION: main

11-18 16:50:27.263: E/AndroidRuntime(1410): java.lang.NullPointerException

11-18 16:50:27.263: E/AndroidRuntime(1410):     at com.compfour.homework.Setup$1.onClick(Setup.java:30)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at android.view.View.performClick(View.java:4240)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at android.view.View$PerformClick.run(View.java:17721)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at android.os.Handler.handleCallback(Handler.java:730)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at android.os.Handler.dispatchMessage(Handler.java:92)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at android.os.Looper.loop(Looper.java:137)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at android.app.ActivityThread.main(ActivityThread.java:5103)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at java.lang.reflect.Method.invokeNative(Native Method)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at java.lang.reflect.Method.invoke(Method.java:525)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)

11-18 16:50:27.263: E/AndroidRuntime(1410):     at dalvik.system.NativeStart.main(Native Method)