Add generic two array concatenation snippet

iluwatar · iluwatar · commit f0fcb7a64a8a · 2017-12-15T22:53:49.000+02:00
diff --git a/README.md b/README.md
@@ -1,3 +1,25 @@
 # Java Snippets
 
 Inspired by [30 seconds of code](https://github.com/Chalarangelo/30-seconds-of-code), this is a collection of reusable Java code snippets.
+
+## How to contribute
+Update the sample application with the snippet and add a test for it. After proving that it works update this README.md.
+
+## Table of Contents
+
+### Array
+* [Generic two array concatenation](#generic-two-array-concatenation)
+
+## Array
+
+### Generic two array concatenation
+
+```java
+    public static <T> T[] arrayConcat(T[] first, T[] second) {
+        T[] result = Arrays.copyOf(first, first.length + second.length);
+        System.arraycopy(second, 0, result, first.length, second.length);
+        return result;
+    }
+```
+
+[⬆ back to top](#table-of-contents)
diff --git a/src/main/java/Library.java b/src/main/java/Library.java
@@ -1,11 +1,21 @@
+import java.util.Arrays;
+
 /*
- * This Java source file was auto generated by running 'gradle buildInit --type java-library'
- * by 'ilkka' at '12/15/17 10:02 PM' with Gradle 2.8
+ * Java Snippets code
  *
- * @author ilkka, @date 12/15/17 10:02 PM
  */
 public class Library {
-    public boolean someLibraryMethod() {
-        return true;
+    /**
+     * Generic 2 array concatenation
+     * Credits: Joachim Sauer https://stackoverflow.com/questions/80476/how-can-i-concatenate-two-arrays-in-java
+     * @param first is the first array (not null)
+     * @param second is the second array (not null)
+     * @param <T> the element type
+     * @return concatenated array
+     */
+    public static <T> T[] arrayConcat(T[] first, T[] second) {
+        T[] result = Arrays.copyOf(first, first.length + second.length);
+        System.arraycopy(second, 0, result, first.length, second.length);
+        return result;
     }
 }
diff --git a/src/test/java/LibraryTest.java b/src/test/java/LibraryTest.java
@@ -2,14 +2,24 @@
 import static org.junit.Assert.*;
 
 /*
- * This Java source file was auto generated by running 'gradle init --type java-library'
- * by 'ilkka' at '12/15/17 10:02 PM' with Gradle 2.8
+ * Java Snippets tests
  *
- * @author ilkka, @date 12/15/17 10:02 PM
  */
 public class LibraryTest {
-    @Test public void testSomeLibraryMethod() {
-        Library classUnderTest = new Library();
-        assertTrue("someLibraryMethod should return 'true'", classUnderTest.someLibraryMethod());
+    /**
+     * Tests for {@link Library#arrayConcat(Object[], Object[])}
+     */
+    @Test
+    public void testArrayConcat() {
+        Integer[] integers = Library.arrayConcat(new Integer[5], new Integer[5]);
+        assertEquals(integers.length, 10);
+        String[] strings = Library.arrayConcat(new String[0], new String[0]);
+        assertEquals(strings.length, 0);
+        try {
+            Double[] doubles = Library.arrayConcat(null, null);
+            fail();
+        } catch (NullPointerException e) {
+            // expected behaviour, everything is fine
+        }
     }
 }
