요청/응답 DTO 관련 문의

안녕하세요, dto 관련 문의드립니다.

요청/응답 DTO를 왜 static으로 만드나요?

이전 데이터가 유지되지 않나요?? 매번 객체를 만들면 안되나요?

@Getter
@Setter
public static class AccountWithdrawReqDto {
    @NotNull
    @Digits(integer = 4, fraction = 4)
    private Long number;
    @NotNull
    @Digits(integer = 4, fraction = 4)
    private Long password;
    @NotNull
    private Long amount;
    @NotEmpty
    @Pattern(regexp = "^(WITHDRAW)$")
    private String transactionType;
}

//ATM -> 계좌
    @Transactional
    public AccountWithdrawRespDto 계좌출금(AccountWithdrawReqDto accountWithdrawReqDto, Long userId) {
        //1. 0원 체크
        if (accountWithdrawReqDto.getAmount() <= 0L)
            throw new CustomApiException("0원 이하의 금액을 출금할 수 없습니다.");

        //2. 출금 계좌 확인
        Account withdrawAccountPS = accountRepository.findByNumber(accountWithdrawReqDto.getNumber())
                .orElseThrow(() -> new CustomApiException("계좌를 찾을 수 없습니다."));

        //3. 본인 확인
        withdrawAccountPS.checkOwner(userId);

        //4. 패스워드 확인
        withdrawAccountPS.checkPassword(accountWithdrawReqDto.getPassword());

        //5. 출금계좌 잔액 확인
//        withdrawAccountPS.checkBalance(accountWithdrawReqDto.getAmount());

        //6. 출금 (잔액 확인이 누락되면 안되므로 출금 메소드에 녹인다!)
        withdrawAccountPS.withdraw(accountWithdrawReqDto.getAmount());

        //7. 거래 내역
        Transaction transaction = Transaction.builder()
                .withdrawAccount(withdrawAccountPS)
                .depositAccount(null)
                .withdrawAccountBalance(withdrawAccountPS.getBalance())
                .depositAccountBalance(null)
                .amount(accountWithdrawReqDto.getAmount())
                .sender(withdrawAccountPS.getNumber().toString())
                .receiver("ATM")
                .transactionType(TransactionEnum.WITHDRAW)
                .build();
        Transaction transactionPS = transactionRepository.save(transaction);

        return new AccountWithdrawRespDto(withdrawAccountPS, transactionPS);
    }