Delete duplicates data value in POI Excel JAVA

i want to delete duplicates data in my excel row. so if there is a duplicate data, the system automatic break the loop and clear entire data in the cycle loop

Example data here

I want to remove all of these duplicates in row Dept Code and just want unique records here. My piece of code is

//sheet 4
                rowIterator_4 = sheet_4.iterator();
                //loop sheet 4   
                while (rowIterator_4.hasNext()) {
                    row_4 = null;               
                    row_4 = rowIterator_4.next();

                    if (row_4 == null) {
                        break;
                    }
                    // skip the header
                    if (rowNo_4 > 1) {
                         String level = getCellValue(row_4.getCell(0));                     
                         String deptCode = getCellValue(row_4.getCell(1));
                         String deptName = getCellValue(row_4.getCell(2));

                        // if all cells within a row are empty, stop process
                        if (
                                (level == null || level.trim().length() == 0) &&
                                (deptCode == null || deptCode.trim().length() == 0) &&
                                (deptName == null || deptName.trim().length() == 0)

                                ) {
                            // exit
                            break;
                        }

                        if (level == null || level.length() == 0) {
                            error += "Level is empty on line " + rowNo_4 + "<br/>";                         
                        }

                        if (deptCode == null || deptCode.length() == 0) {
                            error += "Dept Code is empty on line " + rowNo_4 + "<br/>";
                        }

                        if (deptName == null || deptName.length() == 0) {
                            error += "Dept Name is empty on line " + rowNo_4 + "<br/>";
                        }
                        
                        os = null;
                        os = new ImportExcelToDB();

                        os.setLevel(level);
                        os.setDeptCode(deptCode);
                        os.setDeptName(deptName);

                        if (list3.equals(deptCode)) {
                            error += "Dept Code is duplicate on line " + rowNo_4 + "<br/>";
                            break;
                        }
                        if (os != null) {
                            list3.add(os);
                        }   

                    }
                    rowNo_4++;
                }

Thank you guys