问java.lang.RuntimeException:无法启动活动ComponentInfo: java.lang.ClassCastException:无法转换为android.widget.Button

EN

package co5025.example.com.week10;

            import android.app.FragmentManager;
            import android.content.Intent;
            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.Menu;
            import android.view.MenuItem;
            import android.view.View;
            import android.widget.Button;
            import android.widget.EditText;
            import android.widget.TextView;
            import android.support.v4.app.FragmentManager.BackStackEntry;

            public class MainActivity extends AppCompatActivity implements View.OnClickListener {
                EditText editUsername;
                EditText editPassword;
                TextView errorMessage;
                Button butLogin;
                private FragmentManager.BackStackEntry v;

                @Override
                protected void onCreate(Bundle savedInstanceState) {
                    super.onCreate(savedInstanceState);
                    setContentView(R.layout.activity_main);
                    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
                    setSupportActionBar(toolbar);

                    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
                    fab.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                                    .setAction("Action", null).show();
                        }
                    });
                    editPassword    =   (EditText)  findViewById(R.id.edit_password);
                    editUsername    =   (EditText)  findViewById(R.id.edit_username);
                    butLogin    =   (Button) findViewById(R.id.edit_username);
                    butLogin.setOnClickListener(this);

                    if (getIntent().getBooleanExtra("EXIT", false)) finish();
                }

                @Override
                public void onClick(View view) {
                    if  (checkPassword())   {
                        Intent  i;
                        switch  (v.getId()) {
                            case    R.id.but_login:
                                i   =   new Intent(this,    GameActivity.class);
                                startActivity(i);
                                break;
                        }
                    }else{
                        errorMessage    =   (TextView)  findViewById(R.id.error_message);
                        errorMessage.setText("Error: Incorrect Password/Username. Try again!");
                    }
                }

                @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);
                }

                public  boolean checkPassword(){
                    if  (editUsername.getText().toString().equals("test")   &&
                            (editPassword.getText().toString().equals("1234")))
                        return  true;
                    else
                        return  false;
                }
            }