From 068d3cc439f20e202810a2587f572f8365687741 Mon Sep 17 00:00:00 2001
From: Alexandru Borza <borzaalex18@gmail.com>
Date: Mon, 30 Jan 2023 00:51:12 +0200
Subject: [PATCH] BAEL-6146 - Initialize an ArrayList with All Zeroes or Null
 in Java (#13368)

* initialize arraylist with null or zeros

* configure pom parent

* move code

* delete module
---
 .../InitializeArrayListWithNullOrZeros.java   | 15 ++++
 ...alizeArrayListWithNullOrZerosUnitTest.java | 74 +++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZeros.java
 create mode 100644 core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/initializearraylistwithnullorzeros/InitializeArrayListWithNullOrZerosUnitTest.java

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<Integer> 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<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));
+    }
+}