Printing all variables value from a class

Question

I have a class with information about a Person that looks something like this   public class Contact       private String name      private String location      private String address      private String email      private String phone      private String fax       public String toString                Something here              Getters and setters      I want toString   to return this name    -    this locations       for all variables  I was trying to implement it using reflection as shown from this question but I can t manage to print instance variables   What is the correct way to solve this

User · Answer

Addition with  cletus answer  You have to fetch all model fields upper hierarchy  and set field setAccessible true  to access private members  Here is the full snippet    Override public String toString         StringBuilder result   new StringBuilder        String newLine   System getProperty  line separator         result append getClass   getSimpleName         result append              result append newLine        List lt Field gt  fields   getAllModelFields getClass          for  Field field   fields            result append                try               result append field getName                 result append                    field setAccessible true               result append field get this               catch   IllegalAccessException ex                       System err println ex                     result append newLine             result append           result append newLine        return result toString       private List lt Field gt  getAllModelFields Class aClass        List lt Field gt  fields   new ArrayList lt  gt         do           Collections addAll fields  aClass getDeclaredFields             aClass   aClass getSuperclass          while  aClass    null       return fields

User · Answer

Generic toString   one-liner  using reflection and style customization   import org apache commons lang3 builder ReflectionToStringBuilder  import org apache commons lang3 builder ToStringStyle      public String toString       return ReflectionToStringBuilder toString this  ToStringStyle SHORT PREFIX STYLE

User · Answer

When accessing the field value  pass the instance rather than null   Why not use code generation here  Eclipse  for example  will generate a reasoble toString implementation for you

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From Implementing toString   public String toString       StringBuilder result   new StringBuilder      String newLine   System getProperty  line separator       result append  this getClass   getName        result append    Object         result append newLine        determine fields declared in this class only  no fields of superclass    Field   fields   this getClass   getDeclaredFields         print field names paired with their values   for   Field field   fields          result append            try         result append  field getName            result append                requires access to private field        result append  field get this           catch   IllegalAccessException ex           System out println ex             result append newLine         result append          return result toString

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i will get my answer as follow   import java io IOException  import java io Writer  import java lang reflect Array  import java lang reflect Field  import java util HashMap  import java util Map   public class findclass       public static void main String   args  throws Exception  IllegalAccessException           new findclass   findclass new Object     objectName            new findclass   findclass 1213   int            new findclass   findclass  ssdfs    String                public Map lt String  String gt map new HashMap lt String  String gt          public void findclass Object c String name  throws IllegalArgumentException  IllegalAccessException           if map containsKey c getClass   getName           Integer toHexString c hashCode                   System out println c getClass   getSimpleName       name       map get c getClass   getName           Integer toHexString c hashCode           c                         return           map put c getClass   getName           Integer toHexString c hashCode     name           Class te c getClass            if te equals Integer class   te equals Double class   te equals Float class   te equals Boolean class   te equals Byte class   te equals Long class   te equals String class   te equals Character class                System out println c getClass   getSimpleName       name       c               return                       if te isArray                 if te  int   class  te  char   class  te  double   class  te  float   class  te  byte   class  te  long   class  te  boolean   class                   boolean dotflag true                  for  int i   0  i  lt  Array getLength c   i                          System out println Array get c  i  getClass   getSimpleName       name     i        Array get c  i                                      return                             Object  arr  Object   c              for  Object object   arr                    if object  null                          System out println c getClass   getSimpleName       name     null                    else                       findclass object  name     object getClass   getSimpleName                                                             Field   fields c getClass   getDeclaredFields            for  Field field   fields                field setAccessible true                if field get c   null                   System out println field getType   getSimpleName       name     field getName       null                    continue                             findclass field get c  name     field getName                       if te getSuperclass    Number class  te getSuperclass    Object class  te getSuperclass    null              return          Field  faFields c getClass   getSuperclass   getDeclaredFields             for  Field field   faFields                field setAccessible true                   if field get c   null                       System out println field getType   getSimpleName       name   lt   c getClass   getSuperclass   getSimpleName       field getName       null                        continue                                    Object check field get c                   findclass field get c  name   lt   c getClass   getSuperclass   getSimpleName       field getName                            public void findclass Object c String name Writer writer  throws IllegalArgumentException  IllegalAccessException  IOException           if map containsKey c getClass   getName           Integer toHexString c hashCode                   writer append c getClass   getSimpleName       name       map get c getClass   getName           Integer toHexString c hashCode           c   n                          return           map put c getClass   getName           Integer toHexString c hashCode     name           Class te c getClass            if te equals Integer class   te equals Double class   te equals Float class   te equals Boolean class   te equals Byte class   te equals Long class   te equals String class   te equals Character class                writer append c getClass   getSimpleName       name       c   n                return                       if te isArray                 if te  int   class  te  char   class  te  double   class  te  float   class  te  byte   class  te  long   class  te  boolean   class                   boolean dotflag true                  for  int i   0  i  lt  Array getLength c   i                          writer append Array get c  i  getClass   getSimpleName       name     i        Array get c  i    n                                      return                             Object  arr  Object   c              for  Object object   arr                    if object  null                          writer append c getClass   getSimpleName       name     null    n                     else                       findclass object  name     object getClass   getSimpleName   writer                                                           Field   fields c getClass   getDeclaredFields            for  Field field   fields                field setAccessible true                if field get c   null                   writer append field getType   getSimpleName       name     field getName       null    n                    continue                             findclass field get c  name     field getName   writer                     if te getSuperclass    Number class  te getSuperclass    Object class  te getSuperclass    null              return          Field  faFields c getClass   getSuperclass   getDeclaredFields             for  Field field   faFields                field setAccessible true                   if field get c   null                       writer append field getType   getSimpleName       name   lt   c getClass   getSuperclass   getSimpleName       field getName       null    n                        continue                                    Object check field get c                   findclass field get c  name   lt   c getClass   getSuperclass   getSimpleName       field getName   writer

User · Answer

Why do you want to reinvent the wheel when there are opensource that are already doing the job pretty nicely    Both apache common-langs and spring support some very flexible builder pattern  For apache  here is how you do it reflectively   Override public String toString       return ToStringBuilder reflectionToString this       Here is how you do it if you only want to print fields that you care about      Override public String toString          return new ToStringBuilder this         append  name   name         append  location   location         append  address   address         toString         You can go as far as  styling  your print output with non-default ToStringStyle or even customizing it with your own style   I didn t personally try spring ToStringCreator api  but it looks very similar

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If you are using Eclipse  this should be easy   1 Press Alt Shift S  2 Choose  Generate toString        Enjoy  You can have any template of toString  s   This also works with getter setters

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If the output from ReflectionToStringBuilder toString   is not enough readable for you  here is code that  1  sorts field names alphabetically 2  flags non-null fields with asterisks in the beginning of the line  public static Collection lt Field gt  getAllFields Class lt   gt  type        TreeSet lt Field gt  fields   new TreeSet lt Field gt               new Comparator lt Field gt               Override         public int compare Field o1  Field o2                int res   o1 getName   compareTo o2 getName                 if  0    res                    return res                            res   o1 getDeclaringClass   getSimpleName   compareTo o2 getDeclaringClass   getSimpleName                 if  0    res                    return res                            res   o1 getDeclaringClass   getName   compareTo o2 getDeclaringClass   getName                 return res                        for  Class lt   gt  c   type  c    null  c   c getSuperclass              fields addAll Arrays asList c getDeclaredFields                return fields    public static void printAllFields Object obj        for  Field field   getAllFields obj getClass               field setAccessible true           String name   field getName            Object value   null          try               value   field get obj             catch  IllegalArgumentException   IllegalAccessException e                e printStackTrace                      System out printf   s  s  s    s  n   value  null          field getDeclaringClass   getSimpleName    name  value             test harness   public static void main String   args        A a   new A        a x   1      B b   new B        b x 10      b y 20      System out println                 printAllFields a       System out println                 printAllFields b       System out println                class A       int x      String z    z       Integer b     class B extends A       int y      private double z   12345 6      public int a   55

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Another simple approach is to let Lombok generate the toString method for you   For this    Simply add Lombok to your project Add the annotation  ToString to the definition of your class Compile your class project  and it is done   So for example in your case  your class would look like this    ToString public class Contact       private String name      private String location      private String address      private String email      private String phone      private String fax          Getters and setters      Example of output in this case   Contact name John  location USA  address SF  email foo bar com  phone 99999  fax 88888    More details about how to use the annotation  ToString   NB  You can also let Lombok generate the getters and setters for you  here is the full feature list

[java] Printing all variables value from a class

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