BAEL-5228: Adding code for approaches to concatenating null string in java (#11464)

* commited initial code for hexagonal architecture

* Deleting to check in again

* Deleing to check in again

* Push first code for Hexagonal Architecture

* final code with UT for JSON to Java conversion

* removed hexagonal-architecture code from last commit

* BEL-5071 updated README

* BAEL-5071: Undo README changes and added a nested object in the JSON example.

* BAEL-5071: fixed whitespace/indentation in JsonToJavaClassConversion.java

* BAEL-5151: Added code for getting the first of a String

* BAEL-5151: Renamed Unit Test

* BAEL-5151: Moved the files from core-java-string-operations to core-java-string-operations-3

* BAEL-5151: Replaced tabs with white spaces.

* BAEL-5228: Adding code for approaches to concatening null string in java

* BAEL-5228: Moved file to correct folder and added a UT.

* BAEL-5228: corrected import statements.

* BAEL-5228: corrected last commit.

* BAEL-5228: removed extra import.

* BAEL-5228: renamed UT

Co-authored-by: Vaibhav Jain <vaibhav.ashokjain@vodafone.com>

core-java-modules/core-java-string-operations-4/src/main/java/com/baeldung/concatenation/ConcatenatingNull.java

@@ -0,0 +1,86 @@
+package com.baeldung.concatenation;
+
+import java.util.StringJoiner;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class ConcatenatingNull {
+
+    public static void main(String[] args) {
+        String[] values = { "Java ", null, "", "is ", "great!" };
+
+        concatenateUsingPlusOperator(values);
+        concatenateUsingHelperMethod(values);
+        concatenateUsingStringBuilder(values);
+        concatenateUsingJoin(values);
+        concatenateUsingStringJoiner(values);
+        concatenateUsingCollectorsJoining(values);
+        concatenateUsingStringConcat(values);
+    }
+
+    public static String concatenateUsingStringConcat(String[] values) {
+        String result = "";
+
+        for (String value : values) {
+            result = result.concat(getNonNullString(value));
+        }
+
+        return result;
+    }
+
+    public static String concatenateUsingCollectorsJoining(String[] values) {
+        String result = Stream.of(values).filter(value -> null != value).collect(Collectors.joining(""));
+
+        return result;
+    }
+
+    public static String concatenateUsingStringJoiner(String[] values) {
+        StringJoiner result = new StringJoiner("");
+
+        for (String value : values) {
+            result = result.add(getNonNullString(value));
+        }
+
+        return result.toString();
+    }
+
+    public static String concatenateUsingJoin(String[] values) {
+        String result = String.join("", values);
+
+        return result;
+    }
+
+    public static String concatenateUsingStringBuilder(String[] values) {
+        StringBuilder result = new StringBuilder();
+
+        for (String value : values) {
+            result = result.append(getNonNullString(value));
+        }
+
+        return result.toString();
+    }
+
+    public static String concatenateUsingHelperMethod(String[] values) {
+        String result = "";
+
+        for (String value : values) {
+            result = result + getNonNullString(value);
+        }
+
+        return result;
+    }
+
+    public static String concatenateUsingPlusOperator(String[] values) {
+        String result = "";
+
+        for (String value : values) {
+            result = result + (value == null ? "" : value);
+        }
+
+        return result;
+    }
+
+    private static String getNonNullString(String value) {
+        return value == null ? "" : value;
+    }
+}

core-java-modules/core-java-string-operations-4/src/test/java/com/baeldung/concatenation/ConcatenatingNullUnitTest.java

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+package com.baeldung.concatenation;
+
+import static com.baeldung.concatenation.ConcatenatingNull.concatenateUsingCollectorsJoining;
+import static com.baeldung.concatenation.ConcatenatingNull.concatenateUsingHelperMethod;
+import static com.baeldung.concatenation.ConcatenatingNull.concatenateUsingJoin;
+import static com.baeldung.concatenation.ConcatenatingNull.concatenateUsingPlusOperator;
+import static com.baeldung.concatenation.ConcatenatingNull.concatenateUsingStringBuilder;
+import static com.baeldung.concatenation.ConcatenatingNull.concatenateUsingStringConcat;
+import static com.baeldung.concatenation.ConcatenatingNull.concatenateUsingStringJoiner;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class ConcatenatingNullUnitTest {
+
+    String[] values = { "Java ", null, "", "is ", "great!" };
+
+    @Test
+    public void givenStringElementsWithNull_whenConcatenatedUsingPlus_thenNullIsIgnored() {
+        String result = concatenateUsingPlusOperator(values);
+        assertEquals("Java is great!", result);
+    }
+
+    @Test
+    public void givenStringElementsWithNull_whenConcatenatedUsingHelperMethod_thenNullIsIgnored() {
+        String result = concatenateUsingHelperMethod(values);
+        assertEquals("Java is great!", result);
+    }
+
+    @Test
+    public void givenStringElementsWithNull_whenConcatenatedUsingStringBuilder_thenNullIsIgnored() {
+        String result = concatenateUsingStringBuilder(values);
+        assertEquals("Java is great!", result);
+    }
+
+    @Test
+    public void givenStringElementsWithNull_whenConcatenatedUsingJoin_thenNullIsNotIgnored() {
+        String result = concatenateUsingJoin(values);
+        assertEquals("Java nullis great!", result);
+    }
+
+    @Test
+    public void givenStringElementsWithNull_whenConcatenatedUsingStringJoiner_thenNullIsIgnored() {
+        String result = concatenateUsingStringJoiner(values);
+        assertEquals("Java is great!", result);
+    }
+
+    @Test
+    public void givenStringElementsWithNull_whenConcatenatedUsingCollectorsJoining_thenNullIsIgnored() {
+        String result = concatenateUsingCollectorsJoining(values);
+        assertEquals("Java is great!", result);
+    }
+
+    @Test
+    public void givenStringElementsWithNull_whenConcatenatedUsingStringConcat_thenNullIsIgnored() {
+        String result = concatenateUsingStringConcat(values);
+        assertEquals("Java is great!", result);
+    }
+}