UDF in sap pi

Hi Experts,

I'm new to sap pi and now i'm working on UDF in message mappings. Can anyone explain me the following error.

Source text of object Message Mapping: Trial_Mapping | http://Testnamespace.com has syntax errors:

• Function Add, Line 1: incompatible types
  found : int
  required: java.lang.String
  return var1;
    ^
  Note: /usr/sap/X3S/DVEBMGS00/j2ee/cluster/server0/./temp/classpath_resolver/Map90c28062848211e48dac00000081ed22/source/com/sap/xi/tf/_Trial_Mapping_.java uses or overrides a deprecated API.
  Note: Recompile with -Xlint:deprecation for details.
  Note: /usr/sap/X3S/DVEBMGS00/j2ee/cluster/server0/./temp/classpath_resolver/Map90c28062848211e48dac00000081ed22/source/com/sap/xi/tf/_Trial_Mapping_.java uses unchecked or unsafe operations.
  Note: Recompile with -Xlint:unchecked for details.
• My udf code is
  public String Add(int var1, Container container) throws StreamTransformationException{
  

return var1;

}

My aim is to pass the input var1 to target field but it is showing above error.

Thanks,

satish kumar