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import java.util.Random;
public class Testaa {
public static void main(String[] args) {
String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcedfghijklmnopqrstuvwxyz1234567890";
Random random = new Random();
StringBuffer bu = new StringBuffer();
String a = "";
for (int i = 0; i < 4; i++) {
int number = random.nextInt(str.length());
a = bu.append(str.charAt(number)).toString();
}
System.out.println(a);
}
}