What is the best way to know if all the variables in a Class are null

Question

This would mean that the class was initialized  but the variables were not set   A sample Class   public class User        String id   null      String name   null       public String getId             return id            public void setId String id            this id   id             public String getName             return name            public void setName String name            this name   name            The actual class is huge that I prefer not to check if xyz    null  for each of the variables

User · Answer

If you want this for unit testing I just use the hasNoNullFieldsOrProperties   method from assertj  assertThat myObj  hasNoNullFieldsOrProperties

User · Answer

How about streams   public boolean checkFieldsIsNull Object instance  List lt String gt  fieldNames         return fieldNames stream   allMatch field - gt            try               return Objects isNull instance getClass   getDeclaredField field  get instance              catch  IllegalAccessException   NoSuchFieldException e                return true   You can throw RuntimeException if need

User · Answer

Best  is such a subjective term  -   I would just use the method of checking each individual variable  If your class already has a lot of these  the increase in size is not going to be that much if you do something like   public Boolean anyUnset         if    id    null  return true      if  name    null  return true      return false      Provided you keep everything in the same order  code changes  and automated checking with a script if you re paranoid  will be relatively painless   Alternatively  assuming they re all strings   you could basically put these values into a map of some sort  eg  HashMap  and just keep a list of the key names for that list  That way  you could iterate through the list of keys  checking that the values are set correctly

User · Answer

Field   field   model getClass   getDeclaredFields          for int j 0   j lt field length   j                     String name   field j  getName                                name   name substring 0 1  toUpperCase   name substring 1                String type   field j  getGenericType   toString                    if type equals  class java lang String                        Method m   model getClass   getMethod  get  name                   String value    String  m invoke model                       if value    null                          something to do

User · Answer

Another non-reflective solution for Java 8  in the line of paxdiabo s answer but without using a series of if s  would be to stream all fields and check for nullness   return Stream of id  name           allMatch Objects  isNull     This remains quite easy to maintain while avoiding the reflection hammer

User · Answer

Try something like this   public boolean checkNull   throws IllegalAccessException       for  Field f   getClass   getDeclaredFields            if  f get this     null              return false      return true                  Although it would probably be better to check each variable if at all feasible

User · Answer

This can be done fairly easily using a Lombok generated equals and a static EMPTY object  import lombok Data   public class EmptyCheck       public static void main String   args            User user1   new User             User user2   new User            user2 setName  quot name quot             System out println user1 isEmpty        prints true         System out println user2 isEmpty        prints false             Data     public static class User           private static final User EMPTY   new User             private String id          private String name          private int age           public boolean isEmpty                 return this equals EMPTY                      Prerequisites   Default constructor should not be implemented with custom behavior as that is used to create the EMPTY object All fields of the class should have an implemented equals  built-in Java types are usually not a problem  in case of custom types you can use Lombok   Advantages   No reflection involved As new fields added to the class  this does not require any maintenance as due to Lombok they will be automatically checked in the equals implementation Unlike some other answers this works not just for null checks but also for primitive types which have a non-null default value  e g  if field is int it checks for 0  in case of boolean for false  etc

User · Answer

I think this is a solution that solves your problem easily    return true if any of the parameters is not null     public boolean isUserEmpty     boolean isEmpty  isEmpty    isEmpty   Stream of id              name           anyMatch userParameter - gt  userParameter    null    return isEmpty     Another solution to the same task is  you can change it to if isEmpty  0  checks if all the parameters are null   public boolean isUserEmpty             long isEmpty              isEmpty   Stream of id                      name                       filter userParameter - gt  userParameter    null  count                 if  isEmpty  gt  0                    return true                else                   return false

User · Answer

The best way in my opinion is Reflection as others have recommended  Here s a sample that evaluates each local field for null  If it finds one that is not null  method will return false   public class User        String id   null      String name   null       public String getId             return id             public void setId String id            this id   id             public String getName             return name             public void setName String name            this name   name             public boolean isNull             Field fields     this getClass   getDeclaredFields            for  Field f   fields                try                   Object value   f get this                   if  value    null                        return false                                              catch  IllegalArgumentException e                       TODO Auto-generated catch block                 e printStackTrace                              catch  IllegalAccessException e                       TODO Auto-generated catch block                 e printStackTrace                                      return true              public static void main String args              System out println new User   isNull

[java] What is the best way to know if all the variables in a Class are null?

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