how to check Login with Jsoup

Question

I want to try to check my login program with Jsoup in Android Studio. But Something is wrong. At first I'm login with "Connection.Response". and then after login I get information and put it to element. but when i check with "if" it is not working. How can i check if login was successful? please help me.

this is my code

public class MainActivity extends Activity {
Button b1, b2;
EditText ed1, ed2;

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

    b1 = (Button) findViewById(R.id.button);
    ed1 = (EditText) findViewById(R.id.editText);
    ed2 = (EditText) findViewById(R.id.editText2);
    b2 = (Button) findViewById(R.id.button2);

    b1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String cheak = null;
            Connection.Response response;
            try {
                response = Jsoup.connect("https://ecampus.smu.ac.kr/login/index.php")
                        .data("username", ed1.getText().toString(), "password", ed2.getText().toString())
                        .method(Connection.Method.GET)
                        .timeout(1000)
                        .execute();
                Document doc = Jsoup.connect("http://ecampus.smu.ac.kr/").cookies(response.cookies()).get();
                Elements element = doc.select(".course_subject");
                cheak = element.toString();

                if (cheak != null) {
                    Toast.makeText(getApplicationContext(),
                            "Username and password is correct", Toast.LENGTH_SHORT).show();
                    startActivity(new Intent(MainActivity.this, Next.class));
                } else {
                    Toast.makeText(getApplicationContext(),
                            "Username and password is NOT correct", Toast.LENGTH_SHORT).show();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    });
    b2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            finish();
        }
    });
}

}