Edit Text + Chechbox

package com.alv.app.tugas4;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.graphics.Color;
//generate by @alvinputrau
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    EditText nama,nim;
    Button btn;
    CheckBox cek;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tugas4);

        initialize();
    }

    private void initialize() {
        nama = (EditText) findViewById(R.id.nama);
        nim = (EditText) findViewById(R.id.nim);
        btn = (Button) findViewById(R.id.press);
        cek = (CheckBox) findViewById(R.id.cek);
        btn.setOnClickListener(this);
        cek.setOnClickListener(this);
        btn.setVisibility(View.INVISIBLE);

    }

    public void onClick(View v) {
        // TODO Auto-generated method stub
        final CheckBox checkBox = (CheckBox) findViewById(R.id.cek);
        if (checkBox.isChecked()) {
            btn.setVisibility(View.VISIBLE);
            switch (v.getId()) {
                case R.id.press:
                    final String str = nama.getText().toString();
                    final String stw = nim.getText().toString();
                    AlertDialog.Builder kk = new AlertDialog.Builder(this);
                    kk.setTitle("Apakah data yang anda masukkan sudah benar ?")
                            .setCancelable(true)
                            .setPositiveButton("Ya", new DialogInterface.OnClickListener() {
                                @Override
                                public void onClick(DialogInterface dialog, int id) {
                                    Toast.makeText(getApplicationContext(), stw + " : terima kasih data sudah masuk.",
                                            Toast.LENGTH_LONG).show();
                                    dialog.cancel();
                                }
                            })
                            .setNegativeButton("Tidak", new DialogInterface.OnClickListener() {
                                @Override
                                public void onClick(DialogInterface dialog, int item) {
                                    Toast.makeText(getApplicationContext(), stw + " : jangan ulangin kesalahan.",
                                            Toast.LENGTH_LONG).show();
                                    dialog.cancel();
                                }
                            })
                            .show();
                    break;
            }
        } else
        {btn.setVisibility(View.INVISIBLE);}

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}