Question

您好我有一个国家/地区类，其中包含countryLanguage集。我想为每个国家排序语言。我正在创建视图页面。国家和他的相应语言。县是好的，但其语言不按排序顺序排列。我很困惑在哪个类我使用隔离器和如何。

public class Country implements Serializable{
private Set<CountryLanguage> countryLanguage = new HashSet<CountryLanguage>(0);
//...
}
public class CountryLanguage {
private CountryLanguageID countryLangPK = new CountryLanguageID();
//...
}

复合id类

   public class CountryLanguageID implements Serializable,Comparable<CountryLanguageID>{

private Country country;
private Language language;

@ManyToOne(fetch=FetchType.LAZY)
public Country getCountry() {
    return country;
}
public void setCountry(Country country) {
    this.country = country;
}

@ManyToOne(fetch=FetchType.LAZY)
public Language getLanguage() {
    return language;
}
public void setLanguage(Language language) {
    this.language = language;
}

public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    CountryLanguageID that = (CountryLanguageID) o;

    if (country != null ? !country.equals(that.country) : that.country != null){
        return false;
    }
    if (language != null ? !language.equals(that.language) : that.language != null){
        return false;
    }
    return true;
}
public int hashCode() {
    int result;
    result = (country != null ? country.hashCode() : 0);
    result = 31 * result + (language != null ? language.hashCode() : 0);
    return result;
}
@Override
public int compareTo(CountryLanguageID o) {

    //return this.language.compareTo(o.language);
    return this.getLanguage().getLanguageName().compareTo(o.getLanguage().getLanguageName());
}
}

Answer 1

您可以使用TreeSet代替HashSet来保留countryLanguage：

private Set<CountryLanguage> countryLanguage = new TreeSet<CountryLanguage>(0);

TreeSet的元素使用其自然顺序排序，或者可以使用Comparator进行排序，通常在TreeSet创建时提供。

如果您想使用natural ordering的{{1}}，请CountryLanguage实施CountryLanguage：

Comparable

如果您想使用public class CountryLanguage implements Comparable<CountryLanguage>{ @Override public int compareTo(CountryLanguage cl) { // Comparison logic } ... }订购Comparator的元素，请定义比较器：

countryLanguage

并在创建private static final Comparator<CountryLanguage> COMP = new Comparator<CountryLanguage>() { @Override public int compare(CountryLanguage o1, CountryLanguage o2) { // Compare o1 with o2 } };时使用它：

TreeSet

修改

private Set<CountryLanguage> countryLanguage = new TreeSet<CountryLanguage>(COMP);类型为set。因此，为了对CountryLanguage的元素进行排序，您需要Set<CountryLanguage> countryLanguage实现CountryLanguage（但您已定义Comparable来实现CountryLanguageID）：

在比较Comparable的实例时，您可以使用CountryLanguage属性进行比较：

CountryLanguageID

使用与对象的arraylist相当的sort对象

1 个答案: