BAEL-2546: added Stream.count examples

java-streams/src/test/java/com/baeldung/stream/filter/StreamCountUnitTest.java

@@ -0,0 +1,72 @@
+package com.baeldung.stream.filter;
+
+import org.junit.Test;
+import org.junit.Before;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class StreamCountUnitTest {
+
+    private List<Customer> customers;
+
+    @Before
+    public void setUp() {
+        Customer john = new Customer("John P.", 15, "https://images.unsplash.com/photo-1543320485-d0d5a49c2b2e");
+        Customer sarah = new Customer("Sarah M.", 200);
+        Customer charles = new Customer("Charles B.", 150);
+        Customer mary = new Customer("Mary T.", 1, "https://images.unsplash.com/photo-1543297057-25167dfc180e");
+        customers = Arrays.asList(john, sarah, charles, mary);
+    }
+
+    @Test
+    public void givenListOfCustomers_whenCount_thenGetListSize() {
+        long count = customers
+          .stream()
+          .count();
+
+        assertThat(count).isEqualTo(4L);
+    }
+
+    @Test
+    public void givenListOfCustomers_whenFilterByPointsOver100AndCount_thenGetTwo() {
+        long countBigCustomers = customers
+          .stream()
+          .filter(c -> c.getPoints() > 100)
+          .count();
+
+        assertThat(countBigCustomers).isEqualTo(2L);
+    }
+
+    @Test
+    public void givenListOfCustomers_whenFilterByPointsAndNameAndCount_thenGetOne() {
+        long count = customers
+          .stream()
+          .filter(c -> c.getPoints() > 10 && c.getName().startsWith("Charles"))
+          .count();
+
+        assertThat(count).isEqualTo(1L);
+    }
+
+    @Test
+    public void givenListOfCustomers_whenNoneMatchesFilterAndCount_thenGetZero() {
+        long count = customers
+          .stream()
+          .filter(c -> c.getPoints() > 500)
+          .count();
+
+        assertThat(count).isEqualTo(0L);
+    }
+
+    @Test
+    public void givenListOfCustomers_whenUsingMethodOverHundredPointsAndCount_thenGetTwo() {
+        long count = customers
+          .stream()
+          .filter(Customer::hasOverThousandPoints)
+          .count();
+
+        assertThat(count).isEqualTo(2L);
+    }
+}