Retrieving a random item from ArrayList

Question

I m learning Java and I m having a problem with ArrayList and Random   I have an object called catalogue which has an array list of objects created from another class called item   I need a method in catalogue which returns all the information on one of the itemobjects in the list  The item needs to be selected at random   import java util ArrayList  import java util Random   public class Catalogue       private Random randomGenerator   new Random        private ArrayList lt Item gt  catalogue       public Catalogue                  catalogue   new ArrayList lt Item gt                  public Item anyItem                 int index   randomGenerator nextInt catalogue size             System out println  Managers choice this week    catalogue get index     our recommendation to you            return catalogue get index           When I try to compile I get an error pointing at the System out println line saying         cannot find symbol variable anyItem

User · Answer

As I can see the code  System out println  Managers choice this week    anyItem    our recommendation to you     is unreachable

User · Answer

You must remove the system out println message from below the return  like this   public Item anyItem         randomGenerator   new Random        int index   randomGenerator nextInt catalogue size         Item it   catalogue get index       System out println  Managers choice this week    it    our recommendation to you        return it      the return statement basically says the function will now end  anything included beyond the return statement that is also in scope of it will result in the behavior you experienced

User · Answer

try this       public Item anyItem                 int index   randomGenerator nextInt catalogue size             System out println  Managers choice this week    catalogue get index     our recommendation to you            return catalogue get index           And I strongly suggest you to get a book  such as Ivor Horton s Beginning Java 2

User · Answer

System out println  Managers choice this week    anyItem    our recommendation to you     You havent the variable anyItem initialized or even declared    This code     anyItem     means get value of toString method of Object anyItem  The second thing why this wont work  You have System out print after return statement  Program could never reach tha line   You probably want something like   public Item anyItem         int index   randomGenerator nextInt catalogue size         System out println  Managers choice this week    catalogue get index     our recommendation to you        return catalogue get index        btw  in Java its convetion to place the curly parenthesis on the same line as the declaration of the function

User · Answer

anyItem has never been declared as a variable  so it makes sense that it causes an error   But more importantly  you have code after a return statement and this will cause an unreachable code error

User · Answer

your print comes after you return -- you can never reach that statement  Also  you never declared anyItem to be a variable  You might want  public Item anyItem                 int index   randomGenerator nextInt catalogue size             Item randomItem   catalogue get index           System out println  Managers choice this week    randomItem toString      our recommendation to you            return randomItem          The toString part is just a quickie -- you might want to add a method  getItemDescription  that returns a useful String for this purpose

User · Answer

See https   gist github com nathanosoares 6234e9b06608595e018ca56c7b3d5a57  public static void main String   args        RandomList lt String gt  set   new RandomList lt  gt          set add  a   10       set add  b   10       set add  c   30       set add  d   300        set forEach  t  - gt            System out println t getChance                  HashMap lt String  Integer gt  count   new HashMap lt  gt         IntStream range 0  100  forEach  value  - gt            String str   set raffle            count put str  count getOrDefault str  0    1                count entrySet   stream   forEach entry - gt            System out println String format   s   s   entry getKey    entry getValue                  Output   2 857142857142857  2 857142857142857  8 571428571428571  85 71428571428571  a  2  b  1  c  9  d  88

User · Answer

Here s a better way of doing things   import java util ArrayList  import java util Random   public class facultyquotes       private ArrayList lt String gt  quotes      private String quote1      private String quote2      private String quote3      private String quote4      private String quote5      private String quote6      private String quote7      private String quote8      private String quote9      private String quote10      private String quote11      private String quote12      private String quote13      private String quote14      private String quote15      private String quote16      private String quote17      private String quote18      private String quote19      private String quote20      private String quote21      private String quote22      private String quote23      private String quote24      private String quote25      private String quote26      private String quote27      private String quote28      private String quote29      private String quote30      private int n      Random random       String teacher        facultyquotes                 quotes new ArrayList lt  gt             random new Random            n random nextInt 3    0          quote1  life is hard           quote2  trouble shall come to an end           quote3  never give lose and never get lose           quote4  gamble with the devil and win           quote5  If you don        t build your dream  someone else will hire you to help them build theirs            quote6  The first step toward success is taken when you refuse to be a captive of the environment in which you first find yourself            quote7  When I dare to be powerful          to use my strength in the service of my vision  then it becomes less and less important whether I am afraid            quote8  Whenever you find yourself on the side of the majority  it is time to pause and reflect           quote9  Great minds discuss ideas  average minds discuss events  small minds discuss people            quote10  I have not failed  I        ve just found 10 000 ways that won        t work            quote11  If you don        t value your time  neither will others  Stop giving away your time and talents  Value what you know  amp  start charging for it            quote12  A successful man is one who can lay a firm foundation with the bricks others have thrown at him            quote13  No one can make you feel inferior without your consent            quote14  Let him who would enjoy a good future waste none of his present            quote15  Live as if you were to die tomorrow  Learn as if you were to live forever            quote16  Twenty years from now you will be more disappointed by the things that you didn        t do than by the ones you did do            quote17  The difference between a successful person and others is not a lack of strength  not a lack of knowledge  but rather a lack of will            quote18  Success is about creating benefit for all and enjoying the process  If you focus on this  amp  adopt this definition  success is yours            quote19  I used to want the words        She tried         on my tombstone  Now I want        She did it            quote20  It is our choices  that show what we truly are  far more than our abilities            quote21  You have to learn the rules of the game  And then you have to play better than anyone else            quote22  The successful warrior is the average man  with laser-like focus            quote23  Develop success from failures  Discouragement and failure are two of the surest stepping stones to success            quote24  If you don        t design your own life plan  chances are you        ll fall into someone else        s plan  And guess what they have planned for you  Not much            quote25  The question isn        t who is going to let me  it        s who is going to stop me            quote26  If you genuinely want something  don        t wait for it          teach yourself to be impatient            quote27  Don        t let the fear of losing be greater than the excitement of winning            quote28  But man is not made for defeat  A man can be destroyed but not defeated            quote29  There is nothing permanent except change            quote30  You cannot shake hands with a clenched fist             quotes add quote1           quotes add quote2           quotes add quote3           quotes add quote4           quotes add quote5           quotes add quote6           quotes add quote7           quotes add quote8           quotes add quote9           quotes add quote10           quotes add quote11           quotes add quote12           quotes add quote13           quotes add quote14           quotes add quote15           quotes add quote16           quotes add quote17           quotes add quote18           quotes add quote19           quotes add quote20           quotes add quote21           quotes add quote22           quotes add quote23           quotes add quote24           quotes add quote25           quotes add quote26           quotes add quote27           quotes add quote28           quotes add quote29           quotes add quote30              public void setTeacherandQuote String teacher                this teacher teacher             public void printRandomQuotes                 System out println quotes get n            teacher                public void printAllQuotes                 for  String i   quotes                        System out println i toString

User · Answer

Here you go  using Generics   private  lt T gt  T getRandomItem List lt T gt  list        Random random   new Random        int listSize   list size        int randomIndex   random nextInt listSize       return list get randomIndex

User · Answer

The solution is not good  even you fixed your naming and unreachable statement of that print out    things you should pay attention also  1   randomness seed  and large data  will num of item is so big returned num of that random  lt  itemlist size       you didn t handle multithread  you might get index out of bound exception

User · Answer

public static Item getRandomChestItem List lt Item gt  items        return items get new Random   nextInt items size

User · Answer

anyItem is a method and the System out println call is after your return statement so that won t compile anyway since it is unreachable   Might want to re-write it like   import java util ArrayList  import java util Random   public class Catalogue       private Random randomGenerator      private ArrayList lt Item gt  catalogue       public Catalogue                  catalogue   new ArrayList lt Item gt             randomGenerator   new Random               public Item anyItem                 int index   randomGenerator nextInt catalogue size             Item item   catalogue get index           System out println  Managers choice this week    item    our recommendation to you            return item

[java] Retrieving a random item from ArrayList

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