why my method toString returns 0?

why my method toString returns 0?I have to concat an integer-generated random into a String and when I print the result it's always 0.What should I do?

class Cozi:

public String toString(){
    String concat="";
    Clienti ob = new Clienti();
    for(int i=1;i<=Clienti.getNrClienti();i++){
        concat=" <"+ob.getRandomInt2()+">";
        System.out.print(concat);
    }       
    return concat;
}

class Clienti:

public int serviceTime(){
    System.out.print("\n");
    Random randomServ = new Random();
        for (int idx = 1; idx <= nrClienti; ++idx){
        randomInt2 = randomServ.nextInt(maxServ);
        System.out.println("Generated : " + randomInt2);
    }
    return randomInt2;  
}

!here I have also the methods get and set randomInt2.