create a folder on an SD card

I'm trying to create a folder on the SD card that is named by user inputs, I get no errors when I run it, but it also doesn't create the folder.

the following is all the code I have written for this activity:

public class Jobselection extends AppCompatActivity
     implements OnClickListener {
     Button createButton;
     EditText photogname;
     EditText projnum;
     EditText phase;
     DatePicker datePicker;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_jobselection);
        createButton = (Button) findViewById(R.id.createButton);
        createButton.setOnClickListener(this);
        photogname = (EditText) findViewById(R.id.photographername);
        projnum = (EditText) findViewById(R.id.projectnumber);
        phase = (EditText) findViewById(R.id.phase);
        datePicker = (DatePicker) findViewById(R.id.datePicker);

    }

    public static java.util.Date getDateFromDatePicker(DatePicker datePicker) {
        int day = datePicker.getDayOfMonth();
        int month = datePicker.getMonth();
        int year = datePicker.getYear();
        Calendar calendar = Calendar.getInstance();
        calendar.set(year, month, day);
        return calendar.getTime();
    }
    public void onClick(View createButton) {
    String date = getDateFromDatePicker(datePicker).toString();
    String photog = photogname.getText().toString();
    String proj = projnum.getText().toString() + "." + phase.getText().toString();
    String state;
    state = Environment.getExternalStorageState();
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        File appDirectory = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/" + date + "/" + proj + "/" + photog);
        boolean isDirectoryCreated = appDirectory.exists();
        if (!isDirectoryCreated) {
            isDirectoryCreated = appDirectory.mkdirs();
        }
        if (isDirectoryCreated) {
            Toast.makeText(Jobselection.this, "Folder is created", Toast.LENGTH_LONG).show();
        }
        else
            Log.d("error","dir.already exists");
    }

    Intent launchUnitLoc = new Intent(this, UnitLocation.class);
    startActivity(launchUnitLoc);
}

I just modified your code, here is the full code

public class Jobselection extends AppCompatActivity
implements View.OnClickListener {
private static final int REQUEST_CODE = 200 ;
Button createButton;
EditText photogname;
EditText projnum;
EditText phase;
DatePicker datePicker;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_jobselection);
    createButton = (Button) findViewById(R.id.createButton);
    createButton.setOnClickListener(this);
    photogname = (EditText) findViewById(R.id.editText);//added just to clear error
    projnum = (EditText) findViewById(R.id.editText);//added just to clear erro
    phase = (EditText) findViewById(R.id.editText);// added just to clear error
    datePicker = (DatePicker) findViewById(R.id.datePicker);

}

public static java.util.Date getDateFromDatePicker(DatePicker datePicker) {
    int day = datePicker.getDayOfMonth();
    int month = datePicker.getMonth();
    int year = datePicker.getYear();
    Calendar calendar = Calendar.getInstance();
    calendar.set(year, month, day);
    return calendar.getTime();
}

@RequiresApi(api = Build.VERSION_CODES.M)
public void onClick(View createButton) {
    String date = getDateFromDatePicker(datePicker).toString();
    String photog = "FinalTest";//photogname.getText().toString();just to clear error

    String proj = projnum.getText().toString() + "." + phase.getText().toString();
    String state;
    state = Environment.getExternalStorageState();

    if (Build.VERSION.SDK_INT >= 23) {
        if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
            Log.v("Permisson", "Permission is granted");
        } else {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);
        }
    }
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        File appDirectory = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/" + date + "/" + proj + "/" + photog);
        boolean isDirectoryCreated = appDirectory.exists();
        if (!isDirectoryCreated) {
            isDirectoryCreated = appDirectory.mkdirs();
        }
        if (isDirectoryCreated) {
            Toast.makeText(Jobselection.this, "Folder is created", Toast.LENGTH_LONG).show();
        } else
            Log.d("error", "dir.already exists");
    }
}
}
Intent launchUnitLoc = new Intent(this, UnitLocation.class);
startActivity(launchUnitLoc);

and your Manifest file should be like:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="[your package name]">

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".Jobselection">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

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