How to exit from my application in android

When i press back button on my home screen to exit from my app its not happening. It is going in a loop with my login window so how can i exit from my app??? m new to android here is my home screen code

public class Home extends Activity implements OnClickListener { Button btnLinkToRegister; Button btnLinkTologin; Button btnLinkToCompanyRegister; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.welcome); btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegister); btnLinkToCompanyRegister=(Button)findViewById(R.id.btnLinkToCompanyRegister); btnLinkTologin=(Button) findViewById(R.id.btnLinkTologin); btnLinkToRegister.setOnClickListener(this); btnLinkTologin.setOnClickListener(this); btnLinkToCompanyRegister.setOnClickListener(this); } public void onClick(View v) { switch(v.getId()) { case R.id.btnLinkToRegister: Intent i = new Intent(getBaseContext(), Registration.class); startActivity(i); break; case R.id.btnLinkTologin: Intent j = new Intent(getBaseContext(), Login.class); startActivity(j); break; case R.id.btnLinkToCompanyRegister: Intent k = new Intent(getApplicationContext(), CompanyRegister.class); startActivity(k); } } } 

here is login activity

public class Login extends Activity implements OnClickListener { Button mLogin; Button mRegister; EditText muname; EditText mpassword; DBHelper DB = null; public String status=""; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mRegister = (Button)findViewById(R.id.register); mRegister.setOnClickListener(this); mLogin = (Button)findViewById(R.id.login); mLogin.setOnClickListener(this); } public void onClick(View v) { switch(v.getId()) { case R.id.register: Intent i = new Intent(getBaseContext(), Registration.class); startActivity(i); break; case R.id.login: muname = (EditText)findViewById(R.id.Ledituname); mpassword = (EditText)findViewById(R.id.Leditpw); String username = muname.getText().toString(); String password = mpassword.getText().toString(); if(username.equals("") || username == null) { Toast.makeText(getApplicationContext(), "Please enter User Name", Toast.LENGTH_SHORT).show(); } else if(password.equals("") || password == null) { Toast.makeText(getApplicationContext(), "Please enter your Password", Toast.LENGTH_SHORT).show(); } else { boolean validLogin = validateLogin(username, password, getApplicationContext()); if(validLogin) { if(status.equals("s")) { Intent in = new Intent(getBaseContext(), JSHomePage.class); in.putExtra("UserName", muname.getText().toString()); startActivity(in); } else if(status.equals("c")) { Intent in = new Intent(getBaseContext(), CompView.class); in.putExtra("UserName", muname.getText().toString()); startActivity(in);} } } break; } } private boolean validateLogin(String username, String password, Context baseContext) { DB = new DBHelper(getBaseContext()); SQLiteDatabase db = DB.getReadableDatabase(); String[] columns = {"_id","status"}; String selection = "username=? AND password=?"; String[] selectionArgs = {username,password}; Cursor cursor = null; try{ cursor = db.query(DBHelper.Login_Table, columns, selection, selectionArgs, null, null, null); startManagingCursor(cursor); } catch(Exception e) { e.printStackTrace(); } int numberOfRows = cursor.getCount(); if(numberOfRows <= 0) { Toast.makeText(getApplicationContext(), "User Name and Password miss match..\nPlease Try Again", Toast.LENGTH_LONG).show(); Intent intent = new Intent(getBaseContext(), Login.class); startActivity(intent); return false; } cursor.moveToNext(); status = cursor.getString(cursor.getColumnIndex("status")); startManagingCursor(cursor); return true; } public void onBackPressed() { Intent i = new Intent(Login.this, Home.class); startActivity(i); } public void onDestroy() { super.onDestroy(); DB.close(); } }