title: Trouble with AppcompatActivity - error: cannot find symbol class AppCompatActivity
body: <p>Im using udacity to learn android development and I have ran into a problem. there are a few errors that have come up:</p>
  
  <pre><code>error: package android.v7.app does not exist    
  error: cannot find symbol class AppCompatActivity   
  error: method does not override or implement a method from a supertype  
  error: cannot find symbol variable super    
  error: cannot find symbol method setContentView(int)    
  error: cannot find symbol class openNumbersList 
  error: cannot find symbol method startActivity(Intent)  
  </code></pre>
  
  <p>Everything was working fine but I was following a tutorial and noticed that my imports in my Main Activity didn't match with what was on the tutorial so I changed:</p>
  
  <pre><code>import...
  </code></pre>
  
  <p>to</p>
  
  <pre><code>import android.v7.app.AppCompatActivity; 
  import android.os.Bundle;
  </code></pre>
  
  <p>also even before this, <code>AppCompatActivity</code> was in red:</p>
  
  <p><strong>Main Activity:</strong></p>
  
  <pre><code>package com.example.android.miwok;
  
  import android.content.Intent;
  import android.v7.app.AppCompatActivity;
  import android.os.Bundle;
  import android.view.View;
  
  public class MainActivity extends AppCompatActivity {
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          // Set the content of the activity to use the activity_main.xml layout file
          setContentView(R.layout.activity_main);
      }
  
      public void openNumbersList(View view){
          Intent i = new Intent(this, openNumbersList.class);
          startActivity(i);
      }
  }
  </code></pre>
  
  <p>gradle:</p>
  
  <pre><code>apply plugin: 'com.android.application'
  
  android {
      compileSdkVersion 23
      buildToolsVersion '27.0.3'
  
      defaultConfig {
          applicationId "com.example.android.miwok"
          minSdkVersion 15
          targetSdkVersion 23
          versionCode 1
          versionName "1.0"
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 
              'proguard-rules.pro'
          }
      }
  }
  
  
  dependencies {
      implementation fileTree(dir: 'libs', include: ['*.jar'])
      implementation 'com.android.support.constraint:constraint-layout:1.1.2'
      testImplementation 'junit:junit:4.12'
      implementation 'com.android.support:appcompat-v7:23.3.0'
      implementation 'com.android.support:support-v4:23.3.0'
      implementation 'com.android.support:design:23.3.0'
  
  }
  </code></pre>
  
  <p>hope this helps.</p>