Generate 5 random Strings and add them to a Set in Java

Question

I am a beginner in Java and have the following issue.

How can I generate 5 random strings and add them to a Set?

Answer 1

First, let's create the set:

Set<String> set = new HashSet<>();

Now, let's generate 5 random strings. There are many ways to do this, here is an answer about it. But since you did not ask for a specific length, let's proceed with this:

String randomStr = Long.toHexString(Double.doubleToLongBits(Math.random()));

Now, let's repeat the random generation 5 times:

for (int i = 0; i < 5; i++) {
    set.add(Long.toHexString(Double.doubleToLongBits(Math.random())));
}

Now, the problem is that this does not guarantee the set will have 5 random strings, as we may have similar ones. To ensure that, we should do:

while (set.size() < 5) {
    set.add(Long.toHexString(Double.doubleToLongBits(Math.random())));
}

The code above will continue generating random strings until the set contains at least 5. I'm not checking if it already contains the string because a Set, by definition, contains no duplicate elements. So, adding a duplicate won't increase the size.

Answer 2

You can do something like

import java.util.HashSet;
import java.util.Random;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        Set<String> set = new HashSet<String>();
        Random random = new Random();
        while (set.size() != 5) {
            set.add(String.valueOf((char) (65 + random.nextInt(26))));
        }
        System.out.println(set);
    }
}

A sample run:

[D, X, L, M, N]

Notes:

1. Random.nextInt(n) generates an int from 0 to n-1 where n is an int. Therefore, 65 + random.nextInt(26)) will generate a number from 65 to 90.
2. String.valueOf(c) converts c into a String where c is a char.
3. The ASCII value of A is 65 and that of Z is 90. So, ((char)65) will be printed as A.

Answer 3

UUID

You can use UUID values for your random strings.

Set<String> strings = IntStream.range(0, 5).boxed()
        .map(i -> UUID.randomUUID().toString())
        .collect(Collectors.toSet());

Output:

[174686cc-f1e6-4532-944f-de5a85fa5979, 0151b604-93fa-41cf-8ca8-e872c29e261f, 030c6524-c8cb-4c32-a17b-6189a3a167d5, 3e99e7fd-f143-4af6-bcfc-9b968e9397c9, 11099e22-3c05-45e6-b989-2a3c62acaa15]

Answer 4

This example uses the number values of Unicode Characters to create a string, the Java.util.Random class is used to randomly generate a number:

Code

public static void main(String args[]) {
    Set<String> randomStrings = new HashSet<>();//create the set
    Random random = new Random(); //this creates a random number

    for(int i=0;i<5;i++) { //loop 5 times
        String generatedString = random.ints(60, 122)//(min value, max value) 
                  .limit(10) //sets the string length to 10 characters
                  .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
                  .toString();
        randomStrings.add(generatedString); //add the generatedString to the Set
    }

    //print contents of the Set
    for(String s: randomStrings) {
        System.out.println(s);
    }
}

Output:

pflmmE[jCu
ogofehE<XS
BFbqtHnE_O
Qvu@IDJcI=
Al>BvaLZ@[

Answer 5

Here is one solution (out of many possibilities). Note that this could be condensed into a few statements but then it would be difficult to explain with comments. First, let's get the easiest one done.

        Random r = new Random(23);
        Set<String> stringSet = new HashSet<>();

        for (int i = 0; i < 5; i++) {
            stringSet.add(Integer.toString(r.nextInt()));
        }

        stringSet.forEach(System.out::println);

Yep! Numbers have been converted to Strings. You didn't specify what type of strings.

Moving on...

        Random r = new Random(23);
        Set<String> stringSet = new HashSet<>();

        for (int i = 0; i < 5; i++) {
            // use a Stringbuilder to build it.
            StringBuilder sb = new StringBuilder();
            // length of string between 6 and 10 inclusive
            int len = r.nextInt(5)+6; 

             // now build the string
             while (len-- > 0) {    
                // generate a character from 'a' to 'z' inclusive
                char c = (char)(r.nextInt(26) + 'a'); 
                sb.append(c);
            }

            // and it to the set
            stringSet.add(sb.toString());
        }

        // print them.
        for (String s : stringSet) {
            System.out.println(s);
        }

This run printed

sefmjkzket
qfjklm
dxocur
mldkzcmv
ivqrynsspu

Your output could be different (they are random).

Note that the building of the string uses integers from 0 to 25 inclusive. Since the lower case letters are sequential, you get a to z by just adding a to each number. One could also just index randomly into a string of letters like so:

String alphabet = "abcdefghijlmnopqrstuvwxyz";
index = r.random(26); //0 to 25
char c =alphabet.charAt(index);

As was stated, there are many ways to do this.

Here's a final demo using Streams. The strings are of a different nature.

        String alphabet = "abcdefghijlmnopqrstuvwxyz";
        Set<String> strings = Stream.generate(() -> 1)
                .map(z -> alphabet.substring(r.nextInt(5),
                        r.nextInt(10) + 10))
                .distinct().limit(5).collect(Collectors.toSet());


        strings.forEach(System.out::println);

Print them

cdefghijl
abcdefghij
defghijlmnopqrs
cdefghij
cdefghijlmnopqrs

Answer 6

Alphabet

The solution with using alphabet:

String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int stringLength = 10;

Set<String> strings = IntStream.range(0, 5)
        .mapToObj(i -> IntStream.range(0, stringLength)
                .mapToObj(j -> Character.toString(alphabet.charAt(new Random().nextInt(alphabet.length()))))
                .collect(joining()))
        .collect(toSet());

Output:

[XBZPISNKHR, EBAGPRHQNX, GOCZEBGRFC, YRTQZFQNQJ, DVSUXWEITU]

Answer 7

I don't know why you need to make random strings but I don't think it'll be easy tho I've never tried. Also I don't fully know what you mean by a set but I think you mean combine the strings to make a sentence? If that's the case just do this.

String str = "blah ";
String str2 = "ughhh ";
String str3 = "pshh ";
String together = str + str2 + str3;
System.out.println(together);

output

blah ughhh pshh