Errod in R.id, cannot find symbol variable id.

[aparnakm]

In xml file i have written

<LinearLayout>
..
</LinearLayout>
<EditText>
android:id="@+id/txtusername"
....
</EditText>

In .java file i have written

user = (EditText) findViewById(R.id.txtusername)

i am getting error - cannot find symbol : variable id
i am not getting error for R. After typing R, i am able to get
class,attr,layout,string options. but i am not getting id.
in R.java i have methods for all 3(attr,layout,string) but i dont have it for
id.If i add it i'am getting message R.java is system generated cannot modify it.