Question

How do I fetch unique list of object arrays in below code:

    import java.util.*;

    class t1 {
        public static void main(String[] args) {

            Object[] o1 = new Object[] { null, "[e-mail]", "ENG", "775778435", 1};
            Object[] o2 = new Object[] { null, "[e-mail]", "ENG", "775778435", 1};

            List<Object[]> result = new ArrayList<Object[]>(); 
            result.add(o1); 
            result.add(o2); 

            // The above result list is coming from some DB & I cannot change the structure of above script. 
            // Now, I need to remove the duplicates from this result list meaning I need to find duplicates from the objects within the list.
            // I tried below code but it still prints duplicates. Any help???

            Set<User> setResult = new HashSet<User>();
            User userInfo = null;

            for (Object[] userData : result) {
                userInfo = new User((String)userData[0], (String)userData[1], (String)userData[2], (String)userData[3], (Integer) userData[4]);
                setResult.add(userInfo);
            }

            Iterator it = setResult.iterator();
            while (it.hasNext()) {
                Object o = it.next();

                User u = (User) o;
                System.out.println("non-duplicate = " + u.getEmail());
            }

            // Expected result: non-duplicate = [e-mail]
            // Actual   result: non-duplicate = [e-mail] getting printed twice i.e. duplicate not getting removed!
        }
    }

    class User {
        public String firstName;
        public String email;
        public String language;
        public String productCode;
        public int status;

        public User() {         
        }

        public User(String fName, String userId, String lang, String productCode, int status) {
            this.firstName = fName;
            this.email = userId;
            this.language = lang;
            this.productCode = productCode;
            this.status = status;
        }   

        public String getFirstName() {
            return firstName;
        }

        public void setFirstName(String firstName) {
            this.firstName = firstName;
        }

        public String getEmail() {
            return email;
        }

        public void setEmail(String email) {
            this.email = email;
        }

        public String getLanguage() {
            return language;
        }

        public void setLanguage(String language) {
            this.language = language;
        }

        public String getProductCode() {
            return productCode;
        }

        public void setProductCode(String productCode) {
            this.productCode = productCode;
        }

        public int getStatus() {
            return status;
        }

        public void setStatus(int status) {
            this.status = status;
        }

        @Override
        public int hashCode() {
            int fNameHash = 0;
            int lNameHash = 0;
            int emailHash = 0;
            int langHash = 0;
            int productCodeHash = 0;

            if (this.firstName != null) {
                fNameHash = this.firstName.hashCode();
            }

            if (this.email != null) {
                emailHash = this.email.hashCode();
            }

            if (this.language != null) {
                langHash = this.language.hashCode();
            }

            if (this.productCode != null) {
                productCodeHash = this.productCode.hashCode();
            }

            return (fNameHash + lNameHash + emailHash + langHash + productCodeHash + this.status);
        }

        @Override
        public boolean equals(Object obj) {
            if(obj != null && obj instanceof User) {
                User temp = (User) obj;

                if (this.firstName != null && temp.firstName != null && this.firstName.equalsIgnoreCase(temp.firstName) 
                   && this.email != null && temp.email != null && this.email.equalsIgnoreCase(temp.email) 
                   && this.language != null && temp.language != null && this.language.equalsIgnoreCase(temp.language)
                   && this.productCode != null && temp.productCode != null && this.productCode.equalsIgnoreCase(temp.productCode)
                   && this.status == temp.status) {             
                    return true;
                }
            }
            return false;
        }   
    }

My expected result is to print [e-mail] only once but its getting printed twice!!

Can any one tell me how to correct this code?

Thanks!

Answer 1

The problem is with the firstName value that is null for both objects. Because of this the equals() method return false and both your objects are considered distinct by the Set.

Try changing your equals and hashcode with the following:

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof User)) return false;

    User user = (User) o;

    if (status != user.status) return false;
    if (email != null ? !email.equals(user.email) : user.email != null) return false;
    if (firstName != null ? !firstName.equals(user.firstName) : user.firstName != null) return false;
    if (language != null ? !language.equals(user.language) : user.language != null) return false;
    if (productCode != null ? !productCode.equals(user.productCode) : user.productCode != null) return false;

    return true;
}

@Override
public int hashCode() {
    int result = firstName != null ? firstName.hashCode() : 0;
    result = 31 * result + (email != null ? email.hashCode() : 0);
    result = 31 * result + (language != null ? language.hashCode() : 0);
    result = 31 * result + (productCode != null ? productCode.hashCode() : 0);
    result = 31 * result + status;
    return result;
}

Best way is to have equals and hashcode generated from your IDE as suggested in another answer.