Java Random randomMember(Collection collection)

Description

random Member

License

Apache License

Declaration

public static <T> T randomMember(Collection<T> collection) 

Method Source Code

//package com.java2s;
/*/*  ww  w  .  jav  a2  s  .  co  m*/
Copyright (c) 2012 IBM Corp.
    
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    
http://www.apache.org/licenses/LICENSE-2.0
    
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import java.util.*;

public class Main {
    public static <T> T randomMember(Collection<T> collection) {
        int size = collection.size();
        if (size == 0) {
            return null;
        }
        int ndx = randomInt(0, size);
        int i = 0;
        for (T m : collection) {
            if (i == ndx) {
                return m;
            }
            ++i;
        }
        throw new Error("Could not find member " + ndx);
    }

    public static int randomInt(int fromInclusive, int toExclusive) {
        for (int i = 0; i < 1000; ++i) {
            int val = (int) Math.floor(Math.random() * (toExclusive - fromInclusive)) + fromInclusive;
            //I'm worried that the floating point approx to .99999 * 60453 (whatever) will hit toExclusive
            if (val >= fromInclusive && val < toExclusive) {
                return val;
            }
        }
        throw new Error("Cannot generate random number in [" + fromInclusive + ", " + toExclusive + ")");
    }
}

Related

1. randomIterable(Collection col)
2. randomKey()
3. randomKey()
4. randomLetter()
5. randomList(Collection collection)
6. randomNanoTime()
7. randomNick()
8. randomPassword()
9. randomPermutation(int size)