refactoring : loops - replace loop with pipeline

refactoring/src/main/java/com/example/refactoring/_13_loops/_33_replace_loop_with_pipeline/Author.java

@@ -0,0 +1,25 @@
+package com.example.refactoring._13_loops._33_replace_loop_with_pipeline;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+public class Author {
+
+    private String company;
+
+    private String twitterHandle;
+
+    public Author(String company, String twitterHandle) {
+        this.company = company;
+        this.twitterHandle = twitterHandle;
+    }
+
+    static public List<String> TwitterHandles(List<Author> authors, String company) {
+        return authors.stream()
+                .filter(author -> author.company.equals(company) && Objects.nonNull(author.twitterHandle))
+                .map(author -> author.twitterHandle)
+                .toList();
+    }
+
+}

refactoring/src/main/java/com/example/refactoring/_13_loops/_33_replace_loop_with_pipeline/_before/Author.java

@@ -0,0 +1,29 @@
+package com.example.refactoring._13_loops._33_replace_loop_with_pipeline._before;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Author {
+
+    private String company;
+
+    private String twitterHandle;
+
+    public Author(String company, String twitterHandle) {
+        this.company = company;
+        this.twitterHandle = twitterHandle;
+    }
+
+    static public List<String> TwitterHandles(List<Author> authors, String company) {
+        var result = new ArrayList<String> ();
+        for (Author a : authors) {
+            if (a.company.equals(company)) {
+                var handle = a.twitterHandle;
+                if (handle != null)
+                    result.add(handle);
+            }
+        }
+        return result;
+    }
+
+}

refactoring/src/test/java/com/example/refactoring/_13_loops/_33_replace_loop_with_pipeline/AuthorTest.java

@@ -0,0 +1,19 @@
+package com.example.refactoring._13_loops._33_replace_loop_with_pipeline;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class AuthorTest {
+
+    @Test
+    void twitterHandler() {
+        Author kim = new Author("ms", null);
+        Author lee = new Author("naver", "lee");
+        assertEquals(List.of("lee"), Author.TwitterHandles(List.of(kim, lee), "naver"));
+    }
+
+
+}