Java Collection Random Element randomElement(Collection in)

Description

{ method

License

Apache License

Parameter

Parameter	Description
in	- choices - non-null non-empty

Return

- one choice }

Declaration

public static <T> T randomElement(Collection<T> in) 

Method Source Code

//package com.java2s;
//License from project: Apache License 

import java.util.*;
import java.util.List;

public class Main {
    public static final Random gRandomizer = new Random(System.currentTimeMillis());

    /**{ method/*from   w  w w .ja  v  a  2 s .c  o  m*/
     @name randomElement
     @function - choose an element of an array at random
     @param in - choices - non-null non-empty
     @return - one choice
     }*/
    public static <T> T randomElement(Collection<T> in) {
        int size = in.size();
        if (size == 0)
            return (null);
        int item = 0;
        if (size > 1)
            item = randomInt(size);
        List<T> TheList = new ArrayList<T>(in);
        T ret = TheList.get(item);
        TheList = null;
        return (ret);
    }

    /**{ method
     @name randomElement
     @function - choose an element of an array at random
     @param in - choices - non-null non-empty
     @return - one choice
     }*/
    public static <T> T randomElement(T[] in) {
        if (in.length == 1)
            return (in[0]);
        return (in[randomInt(in.length)]);
    }

    /**{ method
      @name randomElement
      @function - choose an element of an array at random
      @param in - choices - non-null non-empty
      @return - one choice
      }*/
    public static double randomElement(double[] in) {
        if (in.length == 1)
            return (in[0]);
        return (in[randomInt(in.length)]);
    }

    /**{ method
      @name randomElement
      @function - choose an element of an array at random
      @param in - choices - non-null non-empty
      @return - one choice
      }*/
    public static char randomElement(char[] in) {
        if (in.length == 1)
            return (in[0]);
        return (in[randomInt(in.length)]);
    }

    /**{ method
     @name randomElement
     @function - choose an element of an array at random
     @param in - choices - non-null non-empty
     @return - one choice
     }*/
    public static int randomElement(int[] in) {
        if (in.length == 1)
            return (in[0]);
        return (in[randomInt(in.length)]);
    }

    /**{ method
     @name randomElement
     @function - choose an element of an array at random
     @param in - choices - non-null non-empty
     @return - one choice
     }*/
    public static int randomInt(int in) {
        if (in <= 1) {
            if (in == 1)
                return (0);
            throw new IllegalArgumentException("randomInt must take a number > 1");
        }
        int test = gRandomizer.nextInt(in);
        if (test < 0)
            test = -test;
        return (test);
    }
}

Related

1. pollRandom(Collection collection, Random rnd)
2. random(Collection collection)
3. random(Collection coll)
4. random(Collection coll)
5. randomElement(Collection coll)
6. randomIterable(Collection col)
7. rndSubset(final Collection c, final double ratio)
8. sampleWithReplacement(Collection c, int n)
9. selectRandom(Collection set)