Random element choice from String array

Question

public class Elements {
    public static String element_answer = "";
    public String[] elements = new String[118];
    elements[0] = "Hydrogen";
    elements[1] = "Helium";
    elements[2] = "Lithium";
    elements[3] = "Beryllium";
    elements[4] = "Boron";
    (...)
    elements[117] = "Ununoctium";
}

I would like to randomly choose a element out of the array and assign the random choice to the variable element_answer. How could this be done?

Sounds good but you haven't asked a question. Which part specifically are you stuck on? Have you searched how to get a random number in Java? — codeMagic, Aug 03 '15 at 16:05
@OskarKjellin I only added a small section because the real array has 118 entries (118 elements) — user299824, Aug 03 '15 at 16:11
@user299824 Yes there's no need to show all items but i think it's better to post code that actually compiles (your still does not compile) — Oskar Kjellin, Aug 03 '15 at 16:18
@user299824 Do you understand that *array number should start from 0*? I modified that in my pending edit. — hata, Aug 03 '15 at 17:16
possible duplicate of [How to randomly pick an element from an array](http://stackoverflow.com/questions/8065532/how-to-randomly-pick-an-element-from-an-array) — Dan Getz, Aug 04 '15 at 04:21

score 1 · Answer 1 · answered Aug 03 '15 at 16:08

1

Try this:

element_answer = elements[new Random().nextInt(elements.length)];

answered Aug 03 '15 at 16:08

Harish Sridharan

1,070
6
10

I then use p1_button1.setText(elementanswer); to assign it to the text of a button but nothing comes up on the button just NOTHING – user299824 Aug 03 '15 at 16:18
1

I would argue that creating a `new Random()` every time you want to get a new random element will be costly in the long run. I prefer @chayasan 's answer more, where `random` can be stored as an instance field if need be to avoid over reconstructing. – NoseKnowsAll Aug 03 '15 at 16:20
@user299824 Look carefully. You created an array with 113 null references. Your odds of choosing one of those 113 nulls instead of one of the 5 are rather high. I suggest you create your array a little differently. – dsh Aug 03 '15 at 17:00
@dsh OP have mentioned that all the 118 data have real entries in the comment section under the question itself. – Harish Sridharan Aug 03 '15 at 17:01
1

@user299824 you have to post the entire activity for me to point out where you are missing out. – Harish Sridharan Aug 03 '15 at 17:03

score 1 · Answer 2 · answered Aug 03 '15 at 16:10

1

You can do something like this,

Random random = new Random();
element_answer = elements[random.nextInt(elements.length)];

answered Aug 03 '15 at 16:10

Chaya Sandamali

657
9
22

alltooconfusingthereforesleep · Answer 3 · 2015-08-06T16:53:09.500

-1

You could use:

import java.util.Collections;
[...]
Collection.shuffle(elements);
element_answer = elements[0];

It would do the trick. You shuffle the whole list and take the first one which is now some element out of this list. Randomized by the Java Collections.

edited Aug 06 '15 at 16:53

answered Aug 03 '15 at 16:07

alltooconfusingthereforesleep

406
6
18

hata · Answer 4 · 2015-08-03T18:34:10.337

I guess your intention with my ESP (joke) that A Class that returns a String which is randomly chosen from an array of Strings (which are names of chemical elements). If so, below is a possible implement.

Elements.java:

// The Class name of Java starts with upper case as normal
public class Elements {
    // There is no need of this field value.
    // public static String element_answer = "";

    public String[] elements = new String[118];

    // You need a random object
    private Random random = new Random();

    // Inside Constructor you can instantiate Strings in the Array
    public Elements() {
        // Array number starts from '0'.
        // This is quite basic knowledge. 
        elements[0] = "Hydrogen";
        elements[1] = "Helium";
        elements[2] = "Lithium";
        elements[3] = "Beryllium";
        elements[4] = "Boron";
        (...)
        elements[117] = "Ununoctium";
        // So array number starts from '0'
        // that the last number is [array length] - 1
    }

    // You need to define a method.
    // This is basic idea for Java Programmers!
    public String getElementRandom() {
        return elements[random.nextInt(elements.length)];
    }
}

Usage inside your Activity (or somewhere) is:

 // Declare at field
 Elements elements = new Elements();

 (...)

 // somewhere you want to use
 p1_button1.setText(elements.getElementRandom());

Random element choice from String array

4 Answers4