AndroidManifest.xmlactivity_main.xmlMainActivity.java
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.wifistateexample">

    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.codinginflow.wifistateexample.MainActivity">

    <Switch
        android:id="@+id/wifi_switch"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="WiFi is OFF "
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

package com.codinginflow.wifistateexample;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.wifi.WifiManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.CompoundButton;
import android.widget.Switch;

public class MainActivity extends AppCompatActivity {
    private Switch wifiSwitch;
    private WifiManager wifiManager;

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

        wifiSwitch = findViewById(R.id.wifi_switch);
        wifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);

        wifiSwitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if (isChecked) {
                    wifiManager.setWifiEnabled(true);
                    wifiSwitch.setText("WiFi is ON");
                } else {
                    wifiManager.setWifiEnabled(false);
                    wifiSwitch.setText("WiFi is OFF");
                }
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();
        IntentFilter intentFilter = new IntentFilter(WifiManager.WIFI_STATE_CHANGED_ACTION);
        registerReceiver(wifiStateReceiver, intentFilter);
    }

    @Override
    protected void onStop() {
        super.onStop();
        unregisterReceiver(wifiStateReceiver);
    }

    private BroadcastReceiver wifiStateReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            int wifiStateExtra = intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                    WifiManager.WIFI_STATE_UNKNOWN);

            switch (wifiStateExtra) {
                case WifiManager.WIFI_STATE_ENABLED:
                    wifiSwitch.setChecked(true);
                    wifiSwitch.setText("WiFi is ON");
                    break;
                case WifiManager.WIFI_STATE_DISABLED:
                    wifiSwitch.setChecked(false);
                    wifiSwitch.setText("WiFi is OFF");
                    break;
            }
        }
    };
}