Generate a random alpha numeric string

Best Solution

import java.util.Locale;
import java.util.Objects;
import java.util.Random;
public class TestJava {
	public static void main(String[] args) {
		RandomString randomString = new RandomString();
class RandomString {
    //Generate a random string.
    public String nextString() {
        for (int idx = 0; idx < buf.length; ++idx)
            buf[idx] = symbols[random.nextInt(symbols.length)];
        return new String(buf);
    public static final String upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    public static final String lower = upper.toLowerCase(Locale.ROOT);
    public static final String digits = "0123456789";
    public static final String alphanum = upper + lower + digits;
    private final Random random;
    private final char[] symbols;
    private final char[] buf;
    public RandomString(int length, Random random, String symbols) {
        if (length < 1) throw new IllegalArgumentException();
        if (symbols.length() < 2) throw new IllegalArgumentException();
        this.random = Objects.requireNonNull(random);
        this.symbols = alphanum.toCharArray();
        this.buf = new char[length];
    //Create an alphanumeric string generator.
    public RandomString(int length, Random random) {
        this(length, random, alphanum);
    //Create an alphanumeric strings from a secure generator.
    public RandomString(int length) {
        this(length, new SecureRandom());
    //Create session identifiers.
    public RandomString() {

Alpha numeric string with –

import java.util.UUID;
public class TestJava {
	public static void main(String[] args) {
	    String uuid = UUID.randomUUID().toString();	    
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