diff --git a/json-smart/src/main/java/net/minidev/json/JSONObject.java b/json-smart/src/main/java/net/minidev/json/JSONObject.java
index 21d3f89..8a0fcfc 100644
--- a/json-smart/src/main/java/net/minidev/json/JSONObject.java
+++ b/json-smart/src/main/java/net/minidev/json/JSONObject.java
@@ -197,18 +197,27 @@ public void writeJSONString(Appendable out, JSONStyle compression) throws IOExce
 	}
 
 	public void merge(Object o2) {
-		merge(this, o2);
+		merge(this, o2, false);
 	}
 
-	protected static JSONObject merge(JSONObject o1, Object o2) {
+	/**
+	 * merge two JSONObject with overwrite or not
+	 * overwrite = false will not overwrite existing key
+	 * overwrite = true will overwrite the value with o2 of existing key
+	 */
+	public void merge(Object o2, boolean overwrite) {
+		merge(this, o2, overwrite);
+	}
+
+	protected static JSONObject merge(JSONObject o1, Object o2, boolean overwrite) {
 		if (o2 == null)
 			return o1;
 		if (o2 instanceof JSONObject)
-			return merge(o1, (JSONObject) o2);
+			return merge(o1, (JSONObject) o2, overwrite);
 		throw new RuntimeException("JSON merge can not merge JSONObject with " + o2.getClass());
 	}
 
-	private static JSONObject merge(JSONObject o1, JSONObject o2) {
+	private static JSONObject merge(JSONObject o1, JSONObject o2, boolean overwrite) {
 		if (o2 == null)
 			return o1;
 		for (String key : o1.keySet()) {
@@ -221,13 +230,18 @@ private static JSONObject merge(JSONObject o1, JSONObject o2) {
 				continue;
 			}
 			if (value1 instanceof JSONObject) {
-				o1.put(key, merge((JSONObject) value1, value2));
+				o1.put(key, merge((JSONObject) value1, value2, overwrite));
 				continue;
 			}
 			if (value1.equals(value2))
 				continue;
-			if (value1.getClass() .equals(value2.getClass()))
+			if (value1.getClass().equals(value2.getClass())) {
+				if (overwrite) {
+					o1.put(key, value2);
+					continue;
+				}
 				throw new RuntimeException("JSON merge can not merge two " + value1.getClass().getName() + " Object together");
+			}
 			throw new RuntimeException("JSON merge can not merge " + value1.getClass().getName() + " with " + value2.getClass().getName());
 		}
 		for (String key : o2.keySet()) {
diff --git a/json-smart/src/test/java/net/minidev/json/test/JSONObjectTest.java b/json-smart/src/test/java/net/minidev/json/test/JSONObjectTest.java
new file mode 100644
index 0000000..0507f88
--- /dev/null
+++ b/json-smart/src/test/java/net/minidev/json/test/JSONObjectTest.java
@@ -0,0 +1,178 @@
+package net.minidev.json.test;
+
+import net.minidev.json.JSONArray;
+import net.minidev.json.JSONObject;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class JSONObjectTest {
+
+    @Test
+    void mergeIntegerFailed() {
+        JSONObject jsonObject1 = new JSONObject();
+        jsonObject1.appendField("k1", 1);
+        Assertions.assertEquals("{\"k1\":1}", jsonObject1.toJSONString());
+
+        // replace with new value by Map merge
+        jsonObject1.merge("k1", 11, (oldValue, newValue) -> newValue);
+        Assertions.assertEquals("{\"k1\":11}", jsonObject1.toJSONString());
+
+        JSONObject jsonObject3 = new JSONObject();
+        jsonObject3.appendField("k2", 2);
+        jsonObject1.merge(jsonObject3);
+        Assertions.assertEquals("{\"k1\":11,\"k2\":2}", jsonObject1.toJSONString());
+
+        // replace with new value by JSONObject merge will fail
+        Exception exception = Assertions.assertThrows(RuntimeException.class, () -> {
+            JSONObject jsonObject2 = new JSONObject();
+            jsonObject2.appendField("k1", 101);
+            jsonObject1.merge(jsonObject2);
+        });
+
+        Assertions.assertEquals(exception.getMessage(), "JSON merge can not merge two java.lang.Integer Object together");
+    }
+
+    @Test
+    void mergeStringFailed() {
+        JSONObject jsonObject1 = new JSONObject();
+        jsonObject1.appendField("k1", "v1");
+        Assertions.assertEquals("{\"k1\":\"v1\"}", jsonObject1.toJSONString());
+
+        // replace with new value by Map merge
+        jsonObject1.merge("k1", "vNew1", (oldValue, newValue) -> newValue);
+        Assertions.assertEquals("{\"k1\":\"vNew1\"}", jsonObject1.toJSONString());
+
+        JSONObject jsonObject3 = new JSONObject();
+        jsonObject3.appendField("k2", "v2");
+        jsonObject1.merge(jsonObject3);
+        Assertions.assertEquals("{\"k1\":\"vNew1\",\"k2\":\"v2\"}", jsonObject1.toJSONString());
+
+        // replace with new value by JSONObject merge will fail
+        Exception exception = Assertions.assertThrows(RuntimeException.class, () -> {
+            JSONObject jsonObject2 = new JSONObject();
+            jsonObject2.appendField("k1", "vNew2");
+            jsonObject1.merge(jsonObject2);
+            System.out.println(jsonObject1.toJSONString());
+        });
+
+        Assertions.assertEquals(exception.getMessage(), "JSON merge can not merge two java.lang.String Object together");
+    }
+
+    @Test
+    void mergeJsonObjectFailed() {
+        JSONObject jsonObject1 = new JSONObject();
+        jsonObject1.appendField("k1", "v1");
+        Assertions.assertEquals("{\"k1\":\"v1\"}", jsonObject1.toJSONString());
+
+        JSONObject jsonObject2 = new JSONObject();
+        jsonObject2.appendField("k2", jsonObject1);
+        Assertions.assertEquals("{\"k2\":{\"k1\":\"v1\"}}", jsonObject2.toJSONString());
+
+        // replace with new value by JSONObject merge will fail
+        JSONObject jsonObject3 = new JSONObject();
+        jsonObject3.appendField("k1", "vNew1");
+
+        JSONObject jsonObject4 = new JSONObject();
+        jsonObject4.appendField("k2", jsonObject3);
+        Assertions.assertEquals("{\"k2\":{\"k1\":\"vNew1\"}}", jsonObject4.toJSONString());
+
+        Exception exception = Assertions.assertThrows(RuntimeException.class, () -> {
+            jsonObject4.merge(jsonObject2);
+        });
+
+        Assertions.assertEquals(exception.getMessage(), "JSON merge can not merge two java.lang.String Object together");
+    }
+
+    @Test
+    void mergeJsonArraySuccess() {
+        JSONObject jsonObject1 = new JSONObject();
+        jsonObject1.appendField("k1", "v1");
+        JSONObject jsonObject2 = new JSONObject();
+        jsonObject2.appendField("k2", "v2");
+
+        JSONArray jsonArray1 = new JSONArray();
+        jsonArray1.add(jsonObject1);
+        jsonArray1.add(jsonObject2);
+        Assertions.assertEquals("[{\"k1\":\"v1\"},{\"k2\":\"v2\"}]", jsonArray1.toJSONString());
+
+        // replace with new value by JSONObject merge will fail
+        JSONObject jsonObject3 = new JSONObject();
+        jsonObject3.appendField("k1", "vNew1");
+        JSONObject jsonObject4 = new JSONObject();
+        jsonObject4.appendField("k2", "vNew2");
+
+        JSONArray jsonArray2 = new JSONArray();
+        jsonArray2.add(jsonObject3);
+        jsonArray2.add(jsonObject4);
+        Assertions.assertEquals("[{\"k1\":\"vNew1\"},{\"k2\":\"vNew2\"}]", jsonArray2.toJSONString());
+
+        jsonArray2.merge(jsonArray1);
+        Assertions.assertEquals("[{\"k1\":\"vNew1\"},{\"k2\":\"vNew2\"},{\"k1\":\"v1\"},{\"k2\":\"v2\"}]", jsonArray2.toJSONString());
+    }
+
+    @Test
+    void mergeIntegerWithOverwriteSuccess() {
+        JSONObject jsonObject1 = new JSONObject();
+        jsonObject1.appendField("k1", 1);
+        Assertions.assertEquals("{\"k1\":1}", jsonObject1.toJSONString());
+
+        // replace with new value by Map merge
+        jsonObject1.merge("k1", 11, (oldValue, newValue) -> newValue);
+        Assertions.assertEquals("{\"k1\":11}", jsonObject1.toJSONString());
+
+        JSONObject jsonObject3 = new JSONObject();
+        jsonObject3.appendField("k2", 2);
+        jsonObject1.merge(jsonObject3);
+        Assertions.assertEquals("{\"k1\":11,\"k2\":2}", jsonObject1.toJSONString());
+
+        // replace with new value by JSONObject merge with override success
+        JSONObject jsonObject2 = new JSONObject();
+        jsonObject2.appendField("k1", 101);
+        jsonObject1.merge(jsonObject2, true);
+        Assertions.assertEquals("{\"k1\":101,\"k2\":2}", jsonObject1.toJSONString());
+    }
+
+    @Test
+    void mergeStringWithOverwriteSuccess() {
+        JSONObject jsonObject1 = new JSONObject();
+        jsonObject1.appendField("k1", "v1");
+        Assertions.assertEquals("{\"k1\":\"v1\"}", jsonObject1.toJSONString());
+
+        // replace with new value by Map merge
+        jsonObject1.merge("k1", "vNew1", (oldValue, newValue) -> newValue);
+        Assertions.assertEquals("{\"k1\":\"vNew1\"}", jsonObject1.toJSONString());
+
+        JSONObject jsonObject3 = new JSONObject();
+        jsonObject3.appendField("k2", "v2");
+        jsonObject1.merge(jsonObject3);
+        Assertions.assertEquals("{\"k1\":\"vNew1\",\"k2\":\"v2\"}", jsonObject1.toJSONString());
+
+        // replace with new value by JSONObject merge with override success
+        JSONObject jsonObject2 = new JSONObject();
+        jsonObject2.appendField("k1", "vNew2");
+        jsonObject1.merge(jsonObject2, true);
+        Assertions.assertEquals("{\"k1\":\"vNew2\",\"k2\":\"v2\"}", jsonObject1.toJSONString());
+    }
+
+    @Test
+    void mergeJsonObjectWithOverwriteSuccess() {
+        JSONObject jsonObject1 = new JSONObject();
+        jsonObject1.appendField("k1", "v1");
+        Assertions.assertEquals("{\"k1\":\"v1\"}", jsonObject1.toJSONString());
+
+        JSONObject jsonObject2 = new JSONObject();
+        jsonObject2.appendField("k2", jsonObject1);
+        Assertions.assertEquals("{\"k2\":{\"k1\":\"v1\"}}", jsonObject2.toJSONString());
+
+        // JSONObject merge will overwrite jsonObject3 by jsonObject2
+        JSONObject jsonObject3 = new JSONObject();
+        jsonObject3.appendField("k1", "vNew1");
+
+        JSONObject jsonObject4 = new JSONObject();
+        jsonObject4.appendField("k2", jsonObject3);
+        Assertions.assertEquals("{\"k2\":{\"k1\":\"vNew1\"}}", jsonObject4.toJSONString());
+
+        jsonObject4.merge(jsonObject2, true);
+        Assertions.assertEquals("{\"k2\":{\"k1\":\"v1\"}}", jsonObject4.toJSONString());
+    }
+}
\ No newline at end of file