How to call Finish() a separate class?

Question

I have an application where when the user clicks "Back" on MainActivity he displays a AlertDialogin the method onBackPressed() asking if you really want to quit the app. But I created a new class Gerenciar to manage, and put all methods there. The problem is that I am not able to insert the Finish() in this class and call on MainActivity. How to proceed?

1 - Code in MainActivity working:

    public void onBackPressed() {

    android.app.AlertDialog.Builder builder = new android.app.AlertDialog.Builder(this);
    builder.setTitle("Atenção!");
    builder.setMessage("Deseja realmente fechar o app?");
    builder.setPositiveButton("Sim", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface arg0, int arg1) {
            finish();
        }
    });
    builder.setNegativeButton("Não", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {}
    });
    alerta = builder.create();
    alerta.show();
}

2 - Code in class Gerenciar inoperative:

    public void Alertar(){
    android.app.AlertDialog.Builder builder = new android.app.AlertDialog.Builder(context);
    builder.setTitle("Atenção!");
    builder.setMessage("Deseja realmente fechar o app?");
    builder.setPositiveButton("Sim", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {
            activity.finish();             //Finish() não aceita, e com o `activity` aceita, mas quebra a aplicação quando executa
        }
    });
    builder.setNegativeButton("Não", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {}
    });
    alerta = builder.create();
    alerta.show();
}

And I call this method in MainActivity:

    public void onBackPressed() {

    final Gerenciar negGer = new Gerenciar(this);
    negGer.Alertar();
    } 

Answer 1

You need to call the method finish() thus below:

((Activity) context).finish();

A basic example:

public class classA{

    Context context;

    public classA(Context context){
        this.context = context;
    }

    void exemploMetodo(){
        ((Activity)context).finish();
    }
}

Adapting to your code:

public void Alertar() {
    android.app.AlertDialog.Builder builder = new android.app.AlertDialog.Builder(context);
    builder.setTitle("Atenção!");
    builder.setMessage("Deseja realmente fechar o app?");
    builder.setPositiveButton("Sim", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {

            ((Activity) context).finish();

        }
    });
    builder.setNegativeButton("Não", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface arg0, int arg1) {}
    });
    alerta = builder.create();
    alerta.show();
}