decrement JdbcParameter memory used

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterDate.java

@@ -4,7 +4,7 @@ import java.sql.Types;
 import java.util.Calendar;
 import java.util.Date;
 
-public class JdbcParameterDate implements JdbcParameter {
+public final class JdbcParameterDate implements JdbcParameter {
 
     private final Date value;
 

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterDecimal.java

@@ -4,7 +4,7 @@ import java.math.BigDecimal;
 import java.sql.Types;
 import java.util.Calendar;
 
-public class JdbcParameterDecimal implements JdbcParameter {
+public final class JdbcParameterDecimal implements JdbcParameter {
 
     private final BigDecimal value;
 

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterImpl.java

@@ -2,7 +2,7 @@ package com.alibaba.druid.proxy.jdbc;
 
 import java.util.Calendar;
 
-public class JdbcParameterImpl implements JdbcParameter {
+public final class JdbcParameterImpl implements JdbcParameter {
 
     private final int      sqlType;
     private final Object   value;

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterInt.java

@@ -3,7 +3,7 @@ package com.alibaba.druid.proxy.jdbc;
 import java.sql.Types;
 import java.util.Calendar;
 
-public class JdbcParameterInt implements JdbcParameter {
+public final class JdbcParameterInt implements JdbcParameter {
 
     private final int value;
 

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterLong.java

@@ -3,7 +3,7 @@ package com.alibaba.druid.proxy.jdbc;
 import java.sql.Types;
 import java.util.Calendar;
 
-public class JdbcParameterLong implements JdbcParameter {
+public final class JdbcParameterLong implements JdbcParameter {
 
     private final long value;
 

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterNull.java

@@ -2,7 +2,7 @@ package com.alibaba.druid.proxy.jdbc;
 
 import java.util.Calendar;
 
-public class JdbcParameterNull implements JdbcParameter {
+public final class JdbcParameterNull implements JdbcParameter {
 
     private final int sqlType;
 

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterString.java

@@ -3,7 +3,7 @@ package com.alibaba.druid.proxy.jdbc;
 import java.sql.Types;
 import java.util.Calendar;
 
-public class JdbcParameterString implements JdbcParameter {
+public final class JdbcParameterString implements JdbcParameter {
 
     private final String value;
 

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterTimestamp.java

@@ -1,14 +1,14 @@
 package com.alibaba.druid.proxy.jdbc;
 
+import java.sql.Timestamp;
 import java.sql.Types;
 import java.util.Calendar;
-import java.util.Date;
 
-public class JdbcParameterTimestamp implements JdbcParameter {
+public final class JdbcParameterTimestamp implements JdbcParameter {
 
-    private final Date value;
+    private final Timestamp value;
 
-    public JdbcParameterTimestamp(Date value){
+    public JdbcParameterTimestamp(Timestamp value){
         this.value = value;
     }