[map-str-obj-to-str-str] converting a Map<String, Object> to a Map<String, String>. (#14175)

core-java-modules/core-java-collections-maps-6/src/test/java/com/baeldung/map/generictypeconversion/ConvertMapWithTypeParamUnitTest.java

@@ -0,0 +1,92 @@
+package com.baeldung.map.generictypeconversion;
+
+import static java.util.stream.Collectors.toMap;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.math.BigDecimal;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import com.google.common.collect.Maps;
+
+public class ConvertMapWithTypeParamUnitTest {
+    private static final Map<String, Object> MAP1 = Maps.newHashMap();
+
+    static {
+        MAP1.put("K01", "GNU Linux");
+        MAP1.put("K02", "Mac OS");
+        MAP1.put("K03", "MS Windows");
+    }
+
+    private static final Map<String, String> EXPECTED_MAP1 = Maps.newHashMap();
+
+    static {
+        EXPECTED_MAP1.put("K01", "GNU Linux");
+        EXPECTED_MAP1.put("K02", "Mac OS");
+        EXPECTED_MAP1.put("K03", "MS Windows");
+    }
+
+    private static final Map<String, Object> MAP2 = Maps.newHashMap();
+
+    static {
+        MAP2.put("K01", "GNU Linux");
+        MAP2.put("K02", "Mac OS");
+        MAP2.put("K03", BigDecimal.ONE);
+    }
+
+    private static final Map<String, String> EXPECTED_MAP2_STRING_VALUES = Maps.newHashMap();
+
+    static {
+        EXPECTED_MAP2_STRING_VALUES.put("K01", "GNU Linux");
+        EXPECTED_MAP2_STRING_VALUES.put("K02", "Mac OS");
+        EXPECTED_MAP2_STRING_VALUES.put("K03", "1");
+    }
+
+    @Test
+    void whenCastingToMap_shouldGetExpectedResult() {
+        Map<String, String> result = (Map) MAP1;
+        assertEquals(EXPECTED_MAP1, result);
+
+        Map<String, String> result2 = (Map) MAP2;
+        assertFalse(result2.get("K03") instanceof String);
+    }
+
+    Map<String, String> checkAndTransform(Map<String, Object> inputMap) {
+        Map<String, String> result = new HashMap<>();
+        for (Map.Entry<String, Object> entry : inputMap.entrySet()) {
+            try {
+                result.put(entry.getKey(), (String) entry.getValue());
+            } catch (ClassCastException e) {
+                throw e;
+            }
+        }
+        return result;
+    }
+
+    @Test
+    void whenCheckAndTransform_shouldGetExpectedResult() {
+        Map<String, String> result = checkAndTransform(MAP1);
+        assertEquals(EXPECTED_MAP1, result);
+
+        assertThrows(ClassCastException.class, () -> checkAndTransform(MAP2));
+    }
+
+    @Test
+    void whenUsingStringValueOf_shouldGetExpectedResult() {
+        Map<String, String> result = MAP1.entrySet()
+          .stream()
+          .collect(toMap(Map.Entry::getKey, e -> String.valueOf(e.getValue())));
+
+        assertEquals(EXPECTED_MAP1, result);
+
+        Map<String, String> result2 = MAP2.entrySet()
+          .stream()
+          .collect(toMap(Map.Entry::getKey, e -> String.valueOf(e.getValue())));
+
+        assertEquals(EXPECTED_MAP2_STRING_VALUES, result2);
+    }
+}