BAEL-4212 (String) or .toString()? - code + tests

core-java-modules/core-java-string-operations-3/src/main/java/com/baeldung/tostring/StringCastUtils.java

@@ -0,0 +1,10 @@
+package com.baeldung.tostring;
+
+public class StringCastUtils {
+    public static String castToString(Object object) {
+        if (object instanceof String) {
+            return (String) object;
+        }
+        return null;
+    }
+}

core-java-modules/core-java-string-operations-3/src/test/java/com/baeldung/tostring/ToStringUnitTest.java

@@ -0,0 +1,92 @@
+package com.baeldung.tostring;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class ToStringUnitTest {
+    @Test
+    public void givenString_whenCastToObjectAndString_thenSameAndNoException() {
+        String input = "baeldung";
+
+        Object obj = input;
+        String str = (String) obj;
+
+        assertEquals(obj, str);
+        assertEquals(str, input);
+        assertSame(input, str);
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void givenIntegerObject_whenCastToObjectAndString_thenCastClassException() {
+        Integer input = 1234;
+
+        Object obj = input;
+        String str = (String) obj;
+    }
+
+    @Test
+    public void givenNullInteger_whenCastToObjectAndString_thenSameAndNoException() {
+        Integer input = null;
+
+        Object obj = input;
+        String str = (String) obj;
+
+        assertEquals(obj, str);
+        assertEquals(str, input);
+        assertSame(input, str);
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void givenNullInteger_whenToString_thenNullPointerException() {
+        Integer input = null;
+
+        String str = input.toString();
+    }
+
+    @Test
+    public void givenInteger_whenCastToObject_thenToStringEquals() {
+        Integer input = 1234;
+
+        Object obj = input;
+
+        assertEquals("1234", input.toString());
+        assertEquals("1234", obj.toString());
+        assertEquals(input.toString(), obj.toString());
+    }
+
+    @Test
+    public void givenString_whenToString_thenSame() {
+        String str = "baeldung";
+
+        assertEquals("baeldung", str.toString());
+        assertSame(str, str.toString());
+    }
+
+    @Test
+    public void givenString_whenCastToObject_thenCastToStringReturnsSame() {
+        String input = "baeldung";
+
+        Object obj = input;
+
+        assertSame(input, StringCastUtils.castToString(obj));
+    }
+
+    @Test
+    public void givenInteger_whenCastToObject_thenCastToStringReturnsNull() {
+        Integer input = 1234;
+
+        Object obj = input;
+
+        assertEquals(null, StringCastUtils.castToString(obj));
+    }
+
+    @Test
+    public void givenIntegerNull_whenCastToObject_thenCastToStringReturnsNull() {
+        Integer input = null;
+
+        Object obj = input;
+
+        assertEquals(null, StringCastUtils.castToString(obj));
+    }
+}