java - Does every static factory methods internally uses new keyword to create object? -


i checked following commonly used static factory methods , each 1 of them internally uses new keyword create object

  1. valueof()

     public static string more ...valueof(char c) {      char data[] = {c};      return new string(data, true);  }   public static string more ...valueof(int i) {      return integer.tostring(i);  }

  2. tostring() returns return new string(buf, true);

    source: java.lang.string.java

part 2 of relevant source: getinstance()

public static calendar more ...getinstance() {     calendar cal = createcalendar(timezone.getdefaultref(),      locale.getdefault(locale.category.format));     cal.sharedzone = true;     return cal; }

createcalendar method internally creates calendar object using new keyword.

source: java.util.calendar.java

is there static factory method, internally not create object using new keyword?

you have 3 ways :

1) factory types instantiate known @ compile time use new operator.
best way straight , compiler enforces validity of object creation.

2) in particular cases, types instantiate may not known @ compile time.
in case, reflection unavoidable.
relies on class.forname() retrieve class , class.newinstance() method instantiate class.

look example java.net.inetaddress class.
has loadimpl() factory method works in way.
can see class.forname() , class.newinstance() methods may throw "technical" exceptions , these discovered @ runtime.

static inetaddressimpl loadimpl(string implname) {     object impl = null;      /*      * property "impl.prefix" prepended classname      * of implementation object instantiate,      * delegate real work (like native methods).       * property can vary across implementations of java.      * classes.  default empty string "".      */     string prefix = accesscontroller.doprivileged(                   new getpropertyaction("impl.prefix", ""));     try {         impl = class.forname("java.net." + prefix + implname).newinstance();     } catch (classnotfoundexception e) {         system.err.println("class not found: java.net." + prefix +                            implname + ":\ncheck impl.prefix property " +                            "in properties file.");     } catch (instantiationexception e) {         system.err.println("could not instantiate: java.net." + prefix +                            implname + ":\ncheck impl.prefix property " +                            "in properties file.");     } catch (illegalaccessexception e) {         system.err.println("cannot access class: java.net." + prefix +                            implname + ":\ncheck impl.prefix property " +                            "in properties file.");     }      if (impl == null) {         try {             impl = class.forname(implname).newinstance();         } catch (exception e) {             throw new error("system property impl.prefix incorrect");         }     }      return (inetaddressimpl) impl; }

3) sometimes, created object new or newinstance() may cached avoid creating multiple times same object.
may make sense immutable objects.


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