<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <!--Text view to display sensor status-->
    <TextView
        android:id="@+id/sensorStatusTV"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textAlignment="center"
        android:textSize="50dp" />

</RelativeLayout>

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    // Creating variables for text view, 
    // sensor manager and our sensor.
    TextView sensorStatusTV;
    SensorManager sensorManager;
    Sensor proximitySensor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sensorStatusTV = findViewById(R.id.sensorStatusTV);

        // calling sensor service.
        sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);

        // from sensor service we are 
        // calling proximity sensor
        proximitySensor = sensorManager.getDefaultSensor(Sensor.TYPE_PROXIMITY);

        // handling the case if the proximity 
        // sensor is not present in users device.
        if (proximitySensor == null) {
            Toast.makeText(this, "No proximity sensor found in device.", Toast.LENGTH_SHORT).show();
            finish();
        } else {
            // registering our sensor with sensor manager.
            sensorManager.registerListener(proximitySensorEventListener,
                    proximitySensor,
                    SensorManager.SENSOR_DELAY_NORMAL);
        }
    }

    // calling the sensor event class to detect
    // the change in data when sensor starts working.
    SensorEventListener proximitySensorEventListener = new SensorEventListener() {
        @Override
        public void onAccuracyChanged(Sensor sensor, int accuracy) {
            // method to check accuracy changed in sensor.
        }

        @Override
        public void onSensorChanged(SensorEvent event) {
            // check if the sensor type is proximity sensor.
            if (event.sensor.getType() == Sensor.TYPE_PROXIMITY) {
                if (event.values[0] == 0) {
                    // here we are setting our status to our textview..
                    // if sensor event return 0 then object is closed
                    // to sensor else object is away from sensor.
                    sensorStatusTV.setText("Near");
                } else {
                    sensorStatusTV.setText("Away");
                }
            }
        }
    };
}