setSupportActionBar toolbar cannot be applied to (android.widget.Toolbar) error

In your Activity.java import android.support.v7.widget.Toolbar instead of android.widget.Toolbar:

import android.app.ActionBar;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.support.v7.widget.Toolbar;public class rutaActivity extends AppCompactActivity {private Toolbar toolbar;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_ruta);    getSupportActionBar().hide();//Ocultar ActivityBar anterior    toolbar = (Toolbar) findViewById(R.id.app_bar);    setSupportActionBar(toolbar); //NO PROBLEM !!!!

Update:

If you are using androidx, replace

import android.support.v7.widget.Toolbar;import android.support.v7.app.AppCompatActivity;

with newer imports

import androidx.appcompat.widget.Toolbar;import androidx.appcompat.app.AppCompatActivity;

In using toolbar you should extends AppCompatActivity and

import android.support.v7.widget.Toolbar 

For adding a ToolBar that supports Material Design, the official documentation directions are probably the best to follow.

1. Add the v7 appcompat support library.

2. Make your activity extend AppCompatActivity.

   public class MyActivity extends AppCompatActivity {  // ...}

3. Declare NoActionBar in the Manifest.

   <application    android:theme="@style/Theme.AppCompat.Light.NoActionBar"    />

4. Add a toolbar to your activity's xml layout.

   <android.support.v7.widget.Toolbar   android:id="@+id/my_toolbar"   android:theme="@style/ThemeOverlay.AppCompat.ActionBar"   ...   />

5. Call setSupportActionBar in the activity's onCreate.

   @Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_my);    Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);    setSupportActionBar(myToolbar);}

Note: You will have to import the following in the activity.

import android.support.v7.app.AppCompatActivity;import android.support.v7.widget.Toolbar;