A Java example to generate a strong, secure random password containing [a-zA-Z0-9!@#$%&*()_+-=[]?] characters, with a length of 15.

package com.mkyong;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;
public class PasswordGenerator {
    private static final String CHAR_LOWER = "abcdefghijklmnopqrstuvwxyz";
    private static final String CHAR_UPPER = CHAR_LOWER.toUpperCase();
    private static final String NUMBER = "0123456789";
    private static final String OTHER_CHAR = "!@#$%&*()_+-=[]?";
    private static final String PASSWORD_ALLOW_BASE = CHAR_LOWER + CHAR_UPPER + NUMBER + OTHER_CHAR;
    // optional, make it more random
    private static final String PASSWORD_ALLOW_BASE_SHUFFLE = shuffleString(PASSWORD_ALLOW_BASE);
    private static final String PASSWORD_ALLOW = PASSWORD_ALLOW_BASE_SHUFFLE;
    private static SecureRandom random = new SecureRandom();
    public static void main(String[] args) {
        System.out.format("String for password \t\t\t: %s%n", PASSWORD_ALLOW_BASE);
        System.out.format("String for password (shuffle) \t: %s%n%n", PASSWORD_ALLOW);
        // generate 5 random password
        for (int i = 0; i < 5; i++) {
            System.out.println("password : " + generateRandomPassword(15));
            System.out.println("\n");
    public static String generateRandomPassword(int length) {
        if (length < 1) throw new IllegalArgumentException();
        StringBuilder sb = new StringBuilder(length);
        for (int i = 0; i < length; i++) {
            int rndCharAt = random.nextInt(PASSWORD_ALLOW.length());
            char rndChar = PASSWORD_ALLOW.charAt(rndCharAt);
            // debug
            System.out.format("%d\t:\t%c%n", rndCharAt, rndChar);
            sb.append(rndChar);
        return sb.toString();
    // shuffle
    public static String shuffleString(String string) {
        List<String> letters = Arrays.asList(string.split(""));
        Collections.shuffle(letters);
        return letters.stream().collect(Collectors.joining());

Output

String for password 			: abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%&*()_+-=[]?
String for password (shuffle) 	: o]XrVD)-cluv0FPq*mO+[GW8zSbB1EHA7%iyYjTeNs=Qx2@w95kf_ZJCn?3U#p6RI!a$LtKgdMh(4&
70	:	K
23	:	8
77	:	&
50	:	k
17	:	m
59	:	U
14	:	P
57	:	?
65	:	!
67	:	$
22	:	W
8	:	c
18	:	O
1	:	]
11	:	v
password : K8&kmUP?!$WcO]v
50	:	k
57	:	?
53	:	Z
58	:	3
42	:	=
61	:	p
64	:	I
4	:	V
39	:	e
12	:	0
23	:	8
2	:	X
55	:	C
18	:	O
42	:	=
password : k?Z3=pIVe08XCO=
61	:	p
35	:	y
53	:	Z
50	:	k
26	:	b
74	:	h
4	:	V
30	:	H
70	:	K
37	:	j
54	:	J
25	:	S
39	:	e
49	:	5
36	:	Y
password : pyZkbhVHKjJSe5Y
16	:	*
70	:	K
77	:	&
66	:	a
27	:	B
6	:	)
64	:	I
55	:	C
72	:	d
51	:	f
28	:	1
14	:	P
0	:	o
60	:	#
58	:	3
password : *K&aB)ICdf1Po#3
3	:	r
43	:	Q
40	:	N
6	:	)
71	:	g
18	:	O
49	:	5
35	:	y
52	:	_
30	:	H
64	:	I
59	:	U
24	:	z
72	:	d
72	:	d
password : rQN)gO5y_HIUzdd