看项目源码时的疑问

我在网上下了个仓库管理系统项目在看他源码是发现里面的
货币表类有两个货币率类型的Set集合字段，我想问的是货币表类为什么有两个货币率类型的Set集合字段。一个不就可以了吗
货币类代码如下public class Currency implements java.io.Serializable { // Fields private String curId; private String curDesc; private Set currencyratesForCurId = new HashSet(0); private Set currencyratesForCurId1 = new HashSet(0); // Constructors /** default constructor */
public Currency() {
} /** minimal constructor */
public Currency(String curId) {
this.curId = curId;
} /** full constructor */
public Currency(String curId, String curDesc, Set currencyratesForCurId,
Set currencyratesForCurId1) {
this.curId = curId;
this.curDesc = curDesc;
this.currencyratesForCurId = currencyratesForCurId;
this.currencyratesForCurId1 = currencyratesForCurId1;
} // Property accessors public String getCurId() {
return this.curId;
} public void setCurId(String curId) {
this.curId = curId;
} public String getCurDesc() {
return this.curDesc;
} public void setCurDesc(String curDesc) {
this.curDesc = curDesc;
} public Set getCurrencyratesForCurId() {
return this.currencyratesForCurId;
} public void setCurrencyratesForCurId(Set currencyratesForCurId) {
this.currencyratesForCurId = currencyratesForCurId;
} public Set getCurrencyratesForCurId1() {
return this.currencyratesForCurId1;
} public void setCurrencyratesForCurId1(Set currencyratesForCurId1) {
this.currencyratesForCurId1 = currencyratesForCurId1;
}货币率类代码如下
public class Currencyrate implements java.io.Serializable { // Fields private CurrencyrateId id; private Currency currencyByCurId; private Currency currencyByCurId1; // Constructors /** default constructor */
public Currencyrate() {
} /** full constructor */
public Currencyrate(CurrencyrateId id, Currency currencyByCurId,
Currency currencyByCurId1) {
this.id = id;
this.currencyByCurId = currencyByCurId;
this.currencyByCurId1 = currencyByCurId1;
} // Property accessors public CurrencyrateId getId() {
return this.id;
} public void setId(CurrencyrateId id) {
this.id = id;
} public Currency getCurrencyByCurId() {
return this.currencyByCurId;
} public void setCurrencyByCurId(Currency currencyByCurId) {
this.currencyByCurId = currencyByCurId;
} public Currency getCurrencyByCurId1() {
return this.currencyByCurId1;
} public void setCurrencyByCurId1(Currency currencyByCurId1) {
this.currencyByCurId1 = currencyByCurId1;
}