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initialize arraylist with null or zeros

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alexandru.borza 2023-01-29 01:53:53 +02:00
parent 7605f8474c
commit d0a56cfbe7
4 changed files with 122 additions and 0 deletions
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32
core-java-modules/core-java-collections-array-list-2/pom.xml Normal file
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@ -0,0 +1,32 @@
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<artifactId>parent-modules</artifactId>
<groupId>com.baeldung</groupId>
<version>1.0.0-SNAPSHOT</version>
<relativePath>../../pom.xml</relativePath>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>core-java-collections-array-list-2</artifactId>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>9</source>
<target>9</target>
</configuration>
</plugin>
</plugins>
</build>
<properties>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
</properties>
</project>

14
core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/InitializeArrayListWithNullOrZeros.java Normal file
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package com.baeldung;
import java.util.ArrayList;
public class InitializeArrayListWithNullOrZeros {
public static void main(String[] args) {
ArrayList<Integer> arrayList = new ArrayList<>();
for (int i = 0; i< 10; i++) {
arrayList.add(null);
}
}
}

75
core-java-modules/core-java-collections-array-list-2/src/test/java/com/baeldung/InitializeArrayListWithNullOrZerosUnitTest.java Normal file
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package com.baeldung;
import org.junit.Test;
import org.junit.jupiter.api.Assertions;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
public class InitializeArrayListWithNullOrZerosUnitTest {
@Test
public void whenInitializingListWithNCopies_thenListIsCorrectlyPopulated() {
// when
ArrayList<Integer> list = IntStream.of(new int[10])
.boxed()
.collect(Collectors.toCollection(ArrayList::new));
// then
Assertions.assertEquals(10, list.size());
Assertions.assertTrue(list.stream().allMatch(elem -> elem == 0));
}
@Test
public void whenInitializingListWithStream_thenListIsCorrectlyPopulated() {
// when
ArrayList<Integer> listWithZeros = Stream.generate(() -> 0)
.limit(10).collect(Collectors.toCollection(ArrayList::new));
ArrayList<Object> listWithNulls = Stream.generate(() -> null)
.limit(10).collect(Collectors.toCollection(ArrayList::new));
// then
Assertions.assertEquals(10, listWithZeros.size());
Assertions.assertTrue(listWithZeros.stream().allMatch(elem -> elem == 0));
Assertions.assertEquals(10, listWithNulls.size());
Assertions.assertTrue(listWithNulls.stream().allMatch(Objects::isNull));
}
@Test public void whenInitializingListWithIntStream_thenListIsCorrectlyPopulated() {
// when
ArrayList<Integer> list = IntStream.of(new int[10])
.boxed()
.collect(Collectors.toCollection(ArrayList::new));
// then
Assertions.assertEquals(10, list.size());
Assertions.assertTrue(list.stream().allMatch(elem -> elem == 0)); }
@Test
public void whenInitializingListWithAsList_thenListIsCorrectlyPopulated() {
// when
Integer[] integers = new Integer[10];
Arrays.fill(integers, 0);
List<Integer> integerList = new ArrayList<>(Arrays.asList(integers));
// then
Assertions.assertEquals(10, integerList.size());
Assertions.assertTrue(integerList.stream().allMatch(elem -> elem == 0));
}
@Test
public void whenInitializingListWithVector_thenListIsCorrectlyPopulated() {
// when
List<Integer> integerList = new Vector<>() {{setSize(10);}};
// then
Assertions.assertEquals(10, integerList.size());
Assertions.assertTrue(integerList.stream().allMatch(Objects::isNull));
}
}

1
pom.xml
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@ -1134,6 +1134,7 @@
<module>core-java-modules/core-java-collections-set</module>
<module>core-java-modules/core-java-collections-list-4</module>
<module>core-java-modules/core-java-collections-array-list</module>
<module>core-java-modules/core-java-collections-array-list-2</module>
<module>core-java-modules/core-java-collections-maps-4</module>
<module>core-java-modules/core-java-collections-maps-5</module>
<module>core-java-modules/core-java-concurrency-simple</module>