BAEL-9062 (#18346)

Author: wynnteo

core-java-modules/core-java-numbers-10/src/test/java/com/baeldung/comparelong/CompareLongWithSortUnitTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.comparelong;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Test;
+
+public class CompareLongWithSortUnitTest {
+
+    @Test
+    public void givenLongList_whenUseCollectionSortToCompare_thenReturnAsc() {
+        List<Long> numbers = new ArrayList<>(Arrays.asList(500L, 200L, 800L));
+        Collections.sort(numbers);
+        assertEquals(Arrays.asList(200L, 500L, 800L), numbers);
+    }
+
+    @Test
+    public void givenLongList_whenUseCollectionSortToCompareWithReverseComparator_thenReturnDsc() {
+        List<Long> numbers = new ArrayList<>(Arrays.asList(500L, 200L, 800L));
+        Collections.sort(numbers, Comparator.reverseOrder());
+        assertEquals(Arrays.asList(800L, 500L, 200L), numbers);
+    }
+
+    @Test
+    public void givenLongList_whenUseCustomComparator_thenReturnExpectedResult() {
+        List<Long> numbers = new ArrayList<>(Arrays.asList(500L, 200L, 800L));
+        long target = 400L;
+        Collections.sort(numbers, (a, b) -> {
+            long distanceA = Math.abs(a - target);
+            long distanceB = Math.abs(b - target);
+            return Long.compare(distanceA, distanceB);
+        });
+        assertEquals(Arrays.asList(500L, 200L, 800L), numbers);
+    }
+
+    @Test
+    public void givenLongList_whenUseMultipleCriteriaToCompare_thenReturnExpectedResult() {
+        List<Long> numbers = new ArrayList<>(Arrays.asList(-500L, 200L, -800L, 300L));
+        Collections.sort(numbers, Comparator.comparingLong(n -> Math.abs((Long) n))
+            .thenComparingLong(n -> (Long) n));
+
+        assertEquals(Arrays.asList(200L, 300L, -500L, -800L), numbers);
+    }
+
+    @Test
+    public void givenLongListWithNull_whenUsingNullsFirst_thenReturnNullAtFirstPosition() {
+        List<Long> numbers = new ArrayList<>(Arrays.asList(500L, null, 200L, 800L));
+        Collections.sort(numbers, Comparator.nullsFirst(Comparator.naturalOrder()));
+        assertEquals(Arrays.asList(null, 200L, 500L, 800L), numbers);
+    }
+
+    @Test
+    public void givenLongListWithNull_whenUsingNullsLast_thenReturnNullAtLastPosition() {
+        List<Long> numbers = new ArrayList<>(Arrays.asList(500L, null, 200L, 800L));
+        Collections.sort(numbers, Comparator.nullsLast(Comparator.naturalOrder()));
+        assertEquals(Arrays.asList(200L, 500L, 800L, null), numbers);
+    }
+
+    @Test
+    public void givenObjectWithLongAttribute_whenComparingObjectWithLongValue_thenReturnExpectedResult() {
+        List<Transaction> transactions = new ArrayList<>();
+        transactions.add(new Transaction(500L));
+        transactions.add(new Transaction(200L));
+        transactions.add(new Transaction(800L));
+        Collections.sort(transactions, Comparator.comparingLong(Transaction::getAmount));
+        assertEquals(Arrays.asList(200L, 500L, 800L), transactions.stream()
+            .map(Transaction::getAmount)
+            .collect(Collectors.toList()));
+    }
+
+}
+
+class Transaction {
+
+    private Long amount;
+
+    public Transaction(Long amount) {
+        this.amount = amount;
+    }
+
+    public Long getAmount() {
+        return amount;
+    }
+}