[streamOf-vs-intStreamRange] Understanding the Difference Between Str… (#13429)

* [streamOf-vs-intStreamRange] Understanding the Difference Between Stream.of and IntStream.range

* [streamOf-vs-intStreamRange] fix indent

core-java-modules/core-java-streams-4/src/test/java/com/baeldung/streams/streamofvsintstream/DiffBetweenStreamOfAndIntStreamRangeUnitTest.java

@@ -0,0 +1,66 @@
+package com.baeldung.streams.streamofvsintstream;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.TreeSet;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+
+public class DiffBetweenStreamOfAndIntStreamRangeUnitTest {
+    @Test
+    void givenStreamOfAndIntStreamRange_whenPeekSortAndFirst_shouldResultDifferent() {
+        Stream<Integer> normalStream = Stream.of(1, 2, 3, 4, 5);
+        IntStream intStreamByRange = IntStream.range(1, 6);
+        List<Integer> normalStreamPeekResult = new ArrayList<>();
+        List<Integer> intStreamPeekResult = new ArrayList<>();
+
+        // First, the regular Stream
+        normalStream.peek(normalStreamPeekResult::add)
+          .sorted()
+          .findFirst();
+        assertEquals(Arrays.asList(1, 2, 3, 4, 5), normalStreamPeekResult);
+
+        // Then, the IntStream
+        intStreamByRange.peek(intStreamPeekResult::add)
+          .sorted()
+          .findFirst();
+        assertEquals(Arrays.asList(1), intStreamPeekResult);
+    }
+
+    @Test
+    void givenStream_whenPeekAndFirst_shouldHaveOnlyFirstElement() {
+        Stream<Integer> normalStream = Stream.of(1, 2, 3, 4, 5);
+        IntStream intStreamByRange = IntStream.range(1, 6);
+        List<Integer> normalStreamPeekResult = new ArrayList<>();
+        List<Integer> intStreamPeekResult = new ArrayList<>();
+
+        // First, the regular Stream
+        normalStream.peek(normalStreamPeekResult::add)
+          .findFirst();
+        assertEquals(Arrays.asList(1), normalStreamPeekResult);
+
+        // Then, the IntStream
+        intStreamByRange.peek(intStreamPeekResult::add)
+          .findFirst();
+        assertEquals(Arrays.asList(1), intStreamPeekResult);
+    }
+
+    @Test
+    void givenSortedStream_whenPeekSortAndFirst_shouldOnlyHaveOneElement() {
+        List<String> peekResult = new ArrayList<>();
+
+        TreeSet<String> treeSet = new TreeSet<>(Arrays.asList("CCC", "BBB", "AAA", "DDD", "KKK"));
+
+        treeSet.stream()
+          .peek(peekResult::add)
+          .sorted()
+          .findFirst();
+
+        assertEquals(Arrays.asList("AAA"), peekResult);
+    }
+}