create vehicle list

create observer
implement debug text view

app/src/main/java/de/hems/trafficsim/MainActivity.java

@@ -3,12 +3,37 @@ package de.hems.trafficsim;
 import androidx.appcompat.app.AppCompatActivity;
 
 import android.os.Bundle;
+import android.view.View;
+import android.widget.TextView;
 
-public class MainActivity extends AppCompatActivity {
+import java.util.Observable;
+import java.util.Observer;
+
+public class MainActivity extends AppCompatActivity implements Observer {
+
+    protected Track track;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
+        this.track = new Track();
+        this.track.addObserver(this);
+
+    }
+
+    @Override
+    public void update(Observable observable, Object o) {
+        String s = "";
+        for (Vehicle v: this.track.getVehicles()){
+            s+="Pos = " + v.getPosition() +"\n";
+        }
+        TextView view = (TextView) findViewById(R.id.debugTextView);
+        view.setText(s);
+        view.invalidate();
+    }
+
+    public void onStepButtonClick (View view){
+        this.track.timeElapse(50);
     }
 }

app/src/main/java/de/hems/trafficsim/Track.java

@@ -1,16 +1,33 @@
 package de.hems.trafficsim;
 
-import java.util.LinkedList;
+import java.util.ArrayList;
 import java.util.List;
+import java.util.Observable;
 
-public class Track {
+public class Track extends Observable {
     protected List<Vehicle> vehicles;
+    public List<Vehicle> getVehicles() {
+        return vehicles;
+    }
+
+
 
     public Track() {
-        this.vehicles = new LinkedList<>();
+        this.vehicles = createVehiclesList();
+    }
+
+    protected List<Vehicle> createVehiclesList(){
+        List<Vehicle> result = new ArrayList<>();
+        for(int i=0;i<10;i++){
+            Vehicle vehicle = new Vehicle(i, 5, 0.2f);
+            result.add(vehicle);
+        }
+        return result;
     }
 
     public void timeElapse(float timeStep) {
-
+        this.setChanged();
+        this.notifyObservers(this);
+        this.clearChanged();
     }
 }

app/src/main/res/layout/activity_main.xml

@@ -6,4 +6,25 @@
     android:layout_height="match_parent"
     tools:context=".MainActivity">
 
+    <TextView
+        android:id="@+id/debugTextView"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="16dp"
+        android:layout_marginTop="16dp"
+        android:text="TextView"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
+
+    <Button
+        android:id="@+id/stepButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="16dp"
+        android:onClick="onStepButtonClick"
+        android:text="Button"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintHorizontal_bias="0.5"
+        app:layout_constraintStart_toStartOf="parent" />
 </androidx.constraintlayout.widget.ConstraintLayout>