A constructor koyaushe yana mayar da sabuwar misali na tsakiyar takaice ta shi, tare da suna da aka tabbata zuwa aji. A factory method wata hanya ta yau da kullun (sau da yawa static) da ke bubuwa da abubuwa — tana ba ka 'yanci akan sunayi, wanne subtype da za ka mayar, da ko za ka bubuwa sabuwa abu ko a'a.
public class Color {
private final int r, g, b;
private Color(int r, int g, int b) { this.r=r; this.g=g; this.b=b; }
// Named factories: clearer intent than overloaded constructors
public static Color fromRgb(int r, int g, int b) { return new Color(r,g,b); }
public static Color fromHex(String hex) { /* parse */ return new Color(0,0,0); }
// Can return a CACHED instance instead of always allocating
private static final Color BLACK = new Color(0,0,0);
public static Color black() { return BLACK; } // no 'new' every call
}
| Constructor | Factory method | |
|---|---|---|
| Suna | Da tabbata zuwa aji | Sanannun suna (fromHex) |
| Nau'in da za a mayar | Daidai wannan aji | Kowane subtype / interface |
| Asali | Koyaushe sabuwa | Iya ciyar/tara/amfani da bada |
| Za ta iya gazawa sosai | Tana jajera | Zai iya mayar null/Optional |
Optional<User> u = User.tryParse(json); // a constructor can't return Optional
Factories suna ƙara jujiya kuma zsu iya boye abin da ba a bubuwa gaske. Yi amfani da m constructor mai saukalaka don samar sauki; kaura ga factory lokacin da kana da bukatar sunayi, polymorphic returns, ko controller misali.
Factory methods suna bambanta kira daga concrete classes — kana iya mayar da sauya aiki ko misali da aka ciyar ba tare da canja gida ba.
Sun kuma sanya APIs ya bayyana: Color.fromHex("#fff") yana karantawa fiye da constructor overload, kuma sunayi na factory suna guje wa katakaitacincinki na masu constructor gida waɗanda suke da nau'i iri ɗaya.