Need help to correct this error am getting in the program below  Am trying to run this prgram on Android studio here are the error am getting : Error:(39, 19) error: cannot find symbol class OnclickListener Error:(29, 38) error: cannot find symbol method findViewByid(int) Error:(35, 16) error: variable exclaimBtn is already defined in method onCreate(Bundle) Error:(35, 38) error: cannot find symbol method findViewByid(int) Error:(39, 60) error: cannot find symbol class OnClickListner Error:Execution failed for task ':app:compileDebugJavaWithJavac'. > Compilation failed; see the compiler error output for details. package com.ademola.hellogoodbye; 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.TextView; import static android.view.View.*; public class MainActivity extends AppCompatActivity { //DECLARE TEXT REFERENCE TO THE INTERFACE LAYOUT COMPONENT  private TextView greetingTextview; //INDICATES HELLO IS CURRENTLY DISPLAYED  private boolean isHello; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); greetingTextview = (TextView) findViewById(R.id.textView); Button exclaimBtn = (Button) findViewByid(R.id.button); //TASK 3: INITIALIZE GREETINGS  initializeGreeting(); //TASK 4: REGISTER THE LISTENER EVENT FOR THE BOTTON  Button exclaimBtn = (Button) findViewByid(R.id.button); exclaimBtn.setOnclickListener(toggleGreeting); } private final OnclickListener toggleGreeting = new View.OnClickListner() { public void onClick(View btn) { //Task: CONSTRUCT THE TOGGLE GREETING  if (isHello) { isHello = false; grettingTextView.setText(R.string.goodbye); } else { isHello = true; greetingTextView.setText(R.string.hello); } } }; private void initializeGreeting() { isHello = true; } /*  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();  }  });  */   @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(); /oinspection SimplifiableIfStatement  if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } 

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Here is what s in activity_main.xml file

xml version="1.0" encoding="utf-8"?>      

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Here s what in content_main.xml

xml version="1.0" encoding="utf-8"?>      

L a 2:55 LTE Hello EXCLAMATION