public class ActionDTO extends GenericDTO implements
Serializable,Auditable {
// default serial version id, required for
serializable classes.

public static final String ACTION_SUSPEND = "SPN";
public static final String ACTION_DEREGISTER
= "DRR";
public static final String ACTION_REINSTATE = "REI";

private static final long serialVersionUID = 1L;
private Long actionId;
private long accountId;
private Date actionDate;
private String actionType;
private String remarks;
private AccountDTO account;

public ActionDTO() {
}

public ActionDTO(Long accountId, String action,
String remarks,
String updatedBy) {
setAccountId(accountId);
setActionType(action);
setActionDate(new Date());
setRemarks(remarks);
setUpdatedBy(updatedBy);
}

public Long getActionId() {
return this.actionId;
}

public void setActionId(Long actionId) {
this.actionId = actionId;
}

public long getAccountId() {
return this.accountId;
}

public void setAccountId(long accountId) {
this.accountId = accountId;
}

public Date getActionDate() {
return this.actionDate;
}

public void setActionDate(Date actionDate) {
this.actionDate = actionDate;
}

public String getActionType() {
return this.actionType;
}

public void setActionType(String actionType) {
this.actionType = actionType;
}

public String getRemarks() {
return this.remarks;
}

public void setRemarks(String remarks) {
this.remarks = remarks;
}

// bi-directional many-to-one association to
AccountDTO
public AccountDTO getAccount() {
return this.account;
}

public void setAccount(AccountDTO account) {
this.account = account;
}

@Override
public String toString() {
// TODO Auto-generated method stub
return null;
}

}
what is the purpose of @Override
public String toString()...and what will do here ?