[BAEL-6434_charAndString] Difference Between "char" and "String" (#13907)

core-java-modules/core-java-char/src/test/java/com/baeldung/charandstring/DifferenceBetweenCharAndStringUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.charandstring;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+
+import org.junit.jupiter.api.Test;
+
+public class DifferenceBetweenCharAndStringUnitTest {
+
+    @Test
+    void whenPlusTwoChars_thenGetSumAsInteger() {
+        char h = 'H'; // the value is 72
+        char i = 'i'; // the value is 105
+        assertEquals(177, h + i);
+        assertInstanceOf(Integer.class, h + i);
+    }
+
+    @Test
+    void whenPlusTwoStrings_thenConcatenateThem() {
+        String i = "i";
+        String h = "H";
+        assertEquals("Hi", h + i);
+    }
+
+    @Test
+    void whenPlusCharsAndStrings_thenGetExpectedValues() {
+        char c = 'C';
+        assertEquals("C", "" + c);
+
+        char h = 'H'; // the value is 72
+        char i = 'i'; // the value is 105
+        assertEquals("Hi", "" + h + i);
+        assertEquals("Hi", h + "" + i);
+        assertEquals("177", h + i + "");
+    }
+
+    @Test
+    void whenStringChars_thenGetCharArray() {
+        char h = 'h';
+        char e = 'e';
+        char l = 'l';
+        char o = 'o';
+
+        String hello = "hello";
+        assertEquals(h, hello.charAt(0));
+        assertEquals(e, hello.charAt(1));
+        assertEquals(l, hello.charAt(2));
+        assertEquals(l, hello.charAt(3));
+        assertEquals(o, hello.charAt(4));
+
+        char[] chars = new char[] { h, e, l, l, o };
+        char[] charsFromString = hello.toCharArray();
+        assertArrayEquals(chars, charsFromString);
+    }
+}