public class RegisterActivity extends AppCompatActivity {

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

final EditText idText = (EditText) findViewById(R.id.phoneNumber);
final EditText passwordText = (EditText) findViewById(R.id.password);
final EditText nicknameText = (EditText) findViewById(R.id.nickname);
final EditText univText = (EditText) findViewById(R.id.universe);

        Button registerBtn = (Button) findViewById(R.id.registerBtn);		
        registerBtn.setOnClickListener(new View.OnClickListener() {
@Override
            public void onClick(View view) {
                String id = idText.getText().toString();
                String password = passwordText.getText().toString();
                String nickname = nicknameText.getText().toString();
                String univ = univText.getText().toString();

                Response.Listener<String> responseListener = new Response.Listener<String>() {
@Override
                    public void onResponse(String response) {
try {
                            JSONObject jsonResponse = new JSONObject(response);
                            if(success){
                                AlertDialog.Builder builder = new AlertDialog.Builder(RegisterActivity.this);
                                builder.setMessage("회원등록 성공").setPositiveButton("확인",null).create().show();

                                Intent intent = new Intent(RegisterActivity.this, MainActivity.class);
                                RegisterActivity.this.startActivity(intent);
                            }
else{
                                AlertDialog.Builder builder = new AlertDialog.Builder(RegisterActivity.this);
                                builder.setMessage("회원등록 실패").setNegativeButton("다시시도",null).create().show();
                            }
                        }
catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                };
                RegisterRequest registerRequest = new RegisterRequest(id, password, nickname, univ, responseListener);
                RequestQueue queue = Volley.newRequestQueue(RegisterActivity.this);
                queue.add(registerRequest);
            }
        });
    }
}