add @Override annotation

src/main/java/com/alibaba/druid/sql/builder/SQLSelectBuilder.java

@@ -47,5 +47,6 @@ public interface SQLSelectBuilder {
 
     SQLSelectBuilder whereOr(String sql);
 
+    @Override
     String toString();
 }

src/main/java/com/alibaba/druid/sql/builder/impl/SQLDeleteBuilderImpl.java

@@ -138,6 +138,7 @@ public class SQLDeleteBuilderImpl implements SQLDeleteBuilder {
         return new SQLDeleteStatement();
     }
 
+    @Override
     public String toString() {
         return SQLUtils.toSQLString(stmt, dbType);
     }

src/main/java/com/alibaba/druid/sql/builder/impl/SQLSelectBuilderImpl.java

@@ -80,6 +80,7 @@ public class SQLSelectBuilderImpl implements SQLSelectBuilder {
         return stmt;
     }
 
+    @Override
     public SQLSelectBuilderImpl select(String... columns) {
         SQLSelectQueryBlock queryBlock = getQueryBlock();
 
@@ -266,6 +267,7 @@ public class SQLSelectBuilderImpl implements SQLSelectBuilder {
         return new SQLSelectGroupByClause();
     }
 
+    @Override
     public String toString() {
         return SQLUtils.toSQLString(stmt, dbType);
     }

src/main/java/com/alibaba/druid/sql/builder/impl/SQLUpdateBuilderImpl.java

@@ -118,6 +118,7 @@ public class SQLUpdateBuilderImpl extends SQLBuilderImpl implements SQLUpdateBui
         return this;
     }
 
+    @Override
     public SQLUpdateBuilderImpl set(String... items) {
         SQLUpdateStatement update = getSQLUpdateStatement();
         for (String item : items) {
@@ -177,6 +178,7 @@ public class SQLUpdateBuilderImpl extends SQLBuilderImpl implements SQLUpdateBui
         return new SQLUpdateStatement();
     }
     
+    @Override
     public String toString() {
         return SQLUtils.toSQLString(stmt, dbType);
     }