Prevent adding duplicate data into JTable in Java

First, I took BDetails and used Netbeans to add the equals and hashcode methods. This is important, as it provides away to assess if two instances of an object are the same

public class BDetails {

    private String username;
    private String firstName;
    private String lastName;
    private String address;

    public BDetails() {
    }

    public BDetails(String username, String firstName, String lastName, String address) {
        this.username = username;
        this.firstName = firstName;
        this.lastName = lastName;
        this.address = address;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getFirstName() {
        return firstName;
    }

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

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 13 * hash + Objects.hashCode(this.username);
        hash = 13 * hash + Objects.hashCode(this.firstName);
        hash = 13 * hash + Objects.hashCode(this.lastName);
        hash = 13 * hash + Objects.hashCode(this.address);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final BDetails other = (BDetails) obj;
        if (!Objects.equals(this.username, other.username)) {
            return false;
        }
        if (!Objects.equals(this.firstName, other.firstName)) {
            return false;
        }
        if (!Objects.equals(this.lastName, other.lastName)) {
            return false;
        }
        if (!Objects.equals(this.address, other.address)) {
            return false;
        }
        return true;
    }
}

I then create a custom TableModel (I'm bias, but I don't have much love for DefaultTableModel and it makes the next step easier)

public class BDetailsTableModel extends AbstractTableModel {

    private List<BDetails> rows;
    private String[] columnNames = {"User name", "First name", "Last Name", "Address"};

    public BDetailsTableModel(List<BDetails> rows) {
        this.rows = rows;
    }

    @Override
    public int getRowCount() {
        return rows.size();
    }

    @Override
    public String getColumnName(int column) {
        return columnNames[column];
    }

    @Override
    public int getColumnCount() {
        return 4;
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        BDetails details = rows.get(rowIndex);
        switch (columnIndex) {
            case 0:
                return details.getUsername();
            case 1:
                return details.getFirstName();
            case 2:
                return details.getLastName();
            case 3:
                return details.getAddress();
        }
        return null;
    }

}

And finally...

List<BDetails> bList = new Gson().fromJson(json, listType);
//for (BDetails adr : bList) {
//    DefaultTableModel model = (DefaultTableModel) pTable.getModel();
//    Vector<String> row = new Vector<String>();
//    row.add(detail.getUserName());
//    row.add(detail.getFirstName());
//    row.add(detail.getLastName());
//    row.add(detail.getAddress();
//    model.addRow(row);
//}
Set<BDetails> unquie = new HashSet<>(bList);
List<BDetails> rows = new ArrayList<>(unquie);
BDetailsTableModel model = new BDetailsTableModel(rows);
pTable.setModel(model);

Okay, all this does is adds the bList to Set, this will remove all duplicates from the list for us (using the hashcode of the objects), add the results to a ArrayList (because it has a get method) and then supplies that to our BDetailsTableModel

Now, if you don't want to replace the TableModel each time, but instead, add the results it becomes a little more difficult, as you need to manage the possibility that the new set of data might contain duplicates of the old set.

You could add the following to BDetailsTableModel...

public void add(BDetails details) {
    int rowCount = getRowCount();
    if (rows.contains(details)) {
        return;
    }
    rows.add(details);
    fireTableRowsInserted(rowCount, rowCount);
}

public void addAll(List<BDetails> newRows) {
    Set<BDetails> rows = new HashSet<>(newRows);
    addAll(rows);
}

public void addAll(Set<BDetails> newRows) {
    Set<BDetails> allRows = new HashSet<>(rows);
    allRows.addAll(newRows);

    rows = new ArrayList<>(allRows);
    fireTableDataChanged();
}

and instead of creating a new instance of BDetailsTableModel, simply use the existing instance (from pTable) and use the above functionality to add new rows