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random element from list guide (#690) 

* random element from list guide

* refactor

* with removing

* refactor + thread optimized index generation

* refactor

* final review refactor
This commit is contained in:
pared 2016-10-04 18:35:37 +02:00 committed by Grzegorz Piwowarek
parent 2ef8bc2a68
commit 3613428993
1 changed files with 57 additions and 1 deletions
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58
core-java-8/src/test/java/com/baeldung/RandomListElementTest.java
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@ -3,15 +3,71 @@ package com.baeldung;
import org.junit.Test;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;
public class RandomListElementTest {
@Test
public void givenList_whenRandomNumberChosen_shouldReturnARandomElement() {
public void givenList_whenRandomIndexChosen_shouldReturnARandomElementUsingRandom() {
List<Integer> givenList = Arrays.asList(1, 2, 3);
Random rand = new Random();
givenList.get(rand.nextInt(givenList.size()));
}
@Test
public void givenList_whenRandomIndexChosen_shouldReturnARandomElementUsingMathRandom() {
List<Integer> givenList = Arrays.asList(1, 2, 3);
givenList.get((int)(Math.random() * givenList.size()));
}
@Test
public void givenList_whenNumberElementsChosen_shouldReturnRandomElementsRepeat() {
Random rand = new Random();
List<String> givenList = Arrays.asList("one", "two", "three", "four");
int numberOfElements = 2;
for (int i = 0; i < numberOfElements; i++) {
int randomIndex = rand.nextInt(givenList.size());
givenList.get(randomIndex);
}
}
@Test
public void givenList_whenNumberElementsChosen_shouldReturnRandomElementsNoRepeat() {
Random rand = new Random();
List<String> givenList = Arrays.asList("one", "two", "three", "four");
int numberOfElements = 2;
for (int i = 0; i < numberOfElements; i++) {
int randomIndex = rand.nextInt(givenList.size());
givenList.get(randomIndex);
givenList.remove(randomIndex);
}
}
@Test
public void givenList_whenSeriesLengthChosen_shouldReturnRandomSeries() {
List<Integer> givenList = Arrays.asList(1, 2, 3, 4, 5, 6);
Collections.shuffle(givenList);
int randomSeriesLength = 3;
givenList.subList(0, randomSeriesLength - 1);
}
@Test
public void givenList_whenRandomIndexChosen_shouldReturnElementThreadSafely() {
List<Integer> givenList = Arrays.asList(1, 2, 3, 4, 5, 6);
int randomIndex = ThreadLocalRandom.current().nextInt(10);
givenList.get(randomIndex);
}
}