BAEL-2962 Java Multi-line String (#7166)

* added readme

* hexagonal architecture implemented

* Java Multiline String

java-strings-2/src/test/java/com/baeldung/string/MultiLineStringUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.string;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+
+import com.baeldung.string.multiline.MultiLineString;
+
+public class MultiLineStringUnitTest {
+
+    
+    @Test
+    public void whenCompareMultiLineStrings_thenTheyAreAllTheSame() throws IOException {
+        MultiLineString ms = new MultiLineString();
+        assertEquals(ms.stringConcatenation(), ms.stringJoin());
+        assertEquals(ms.stringJoin(), ms.stringBuilder());
+        assertEquals(ms.stringBuilder(), ms.guavaJoiner());
+        assertEquals(ms.guavaJoiner(), ms.loadFromFile());
+    }
+    
+}