Why is startActivity causing my app to crash? - android-studio

Question

When the myincome button is clicked, my app crashes, and i'm not sure why. My manifest looks right to me. What is causing it to crash? Most other questions similar to mine were answered by missing to include the activity on the manifest, but mine is already on there. I appreciate any feedback.
StartingActivity:
public class StartingActivity extends AppCompatActivity
{
private TextView myincome;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_starting);
myincome = (TextView) findViewById(R.id.myIncome);
myincome.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
// Start DetailActivity
Intent j = new Intent(StartingActivity.this, DetailActivity.class);
startActivity(j);
}
});
}
}
DetailActivity:
public class DetailActivity extends AppCompatActivity
{
private TextView back;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail); //default
back = (TextView)findViewById(R.id.back);
//back button
back.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
finish();
}
});
}
Manifest:
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity
android:name=".StartingActivity"
android:screenOrientation="portrait">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
<activity android:name=".DetailActivity">
</activity>
<activity android:name=".CategoriesActivity">
</activity>
</application>

Answer 1

Look at Run log. It must be said something like
java.lang.NullPointerException: Attempt to invoke virtual method 'setOnClickListener()' on a null object reference
pointing at line
myincome.setOnClickListener(new View.OnClickListener()
So myincome is null because you didn't assign anything to it.