diff --git a/core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZeros.java b/core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZeros.java new file mode 100644 index 0000000000..66862791aa --- /dev/null +++ b/core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZeros.java @@ -0,0 +1,15 @@ +package com.baeldung.initializearraylistwithnullorzeros; + +import java.util.ArrayList; + +public class InitializeArrayListWithNullOrZeros { + + public static void main(String[] args) { + + ArrayList arrayList = new ArrayList<>(); + for (int i = 0; i< 10; i++) { + arrayList.add(null); + } + } +} + diff --git a/core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZerosUnitTest.java b/core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZerosUnitTest.java new file mode 100644 index 0000000000..00987fa198 --- /dev/null +++ b/core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZerosUnitTest.java @@ -0,0 +1,74 @@ +package com.baeldung.initializearraylistwithnullorzeros; + +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 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 listWithZeros = Stream.generate(() -> 0) + .limit(10).collect(Collectors.toCollection(ArrayList::new)); + + ArrayList 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 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 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 integerList = new Vector<>() {{setSize(10);}}; + + // then + Assertions.assertEquals(10, integerList.size()); + Assertions.assertTrue(integerList.stream().allMatch(Objects::isNull)); + } +}