[list<str>-to-list<int>] Convert a List of Strings to a List of Integers (#14244)

core-java-modules/core-java-collections-conversions-2/src/test/java/com/baeldung/strlisttointlist/StringListToIntListUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.strlisttointlist;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.jupiter.api.Test;
+
+import com.google.common.base.Function;
+import com.google.common.collect.Lists;
+
+public class StringListToIntListUnitTest {
+    private final static List<String> STRING_LIST = Arrays.asList("1", "2", "3", "4", "5", "6", "7");
+    private final static List<Integer> EXPECTED_LIST = Arrays.asList(1, 2, 3, 4, 5, 6, 7);
+
+    @Test
+    void whenUsingStream_thenGetExpectedIntegerList() {
+        List<Integer> result = STRING_LIST.stream()
+          .map(Integer::valueOf)
+          .collect(Collectors.toList());
+        assertEquals(EXPECTED_LIST, result);
+    }
+
+    @Test
+    void whenUsingLoop_thenGetExpectedIntegerList() {
+        List<Integer> result = new ArrayList<>(STRING_LIST.size());
+        for (String s : STRING_LIST) {
+            result.add(Integer.valueOf(s));
+        }
+        assertEquals(EXPECTED_LIST, result);
+    }
+
+    @Test
+    void whenUsingGuava_thenGetExpectedIntegerList() {
+        List<Integer> result = Lists.transform(STRING_LIST, new Function<String, Integer>() {
+            @Override
+            public Integer apply(String input) {
+                return Integer.valueOf(input);
+            }
+        });
+        assertEquals(EXPECTED_LIST, result);
+    }
+}