users does not define no argument constructor [duplicate]

Question

i kept getting this error "users does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped." Tried everything, no idea why it happen.

public void retrievingUserInfo(){      databaseUserID.addValueEventListener(new ValueEventListener() {         @Override         public void onDataChange(DataSnapshot dataSnapshot) {              //clearing the previous userinfo list             Users_Info.clear();              //iterating through all the nodes             for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {                 //getting userinfo                 users userinfo = postSnapshot.getValue(users.class);                 //adding userinfo to the list                 Users_Info.add(userinfo);             }         }          @Override         public void onCancelled(DatabaseError databaseError) {          }     }); } 

users.class

@Keep public class users {      public String user_id, address, contact, name;      public users(String user_id, String address, String contact,String name)      {}   } 

Answer 1

JavaBeans require a no-argument constructor to be present.

When a Java class has no constructors at all, there is a default no-arg constructor automatically added to it by the compiler. The moment you define any constructor in the class, the default no-arg constructor goes away.

In your code, your users class defines such a constructor that contains arguments:

public users(String user_id, String address, String contact,String name)  {} 

As long as that constructor is present, and you don't define a no-arg constructor, that class will not have one.

To resolve this, you either need to remove that constructor from the class, or manually add a no-arg constructor to it:

public users() {}