Android : How to sort array object by specific string field?

This is the class of my object (I need timestamp is a string):

public class Evento{
    public String timestamp;

    public Evento(String timestamp) {
        super();
        this.timestamp = timestamp;
    }
    public String getTimestamp() {
        return timestamp;
    }
}

In my activity I have:

Evento evento = new Evento[10];
for(int i = 0; i<10; i++)
    evento[i] = new Evento(/*Casual String timestamp*/);

Then I have populated the array, how can I sort it by the timestamp inserted?