The operator dublu două puncte (::). , de asemenea cunoscut ca si operator de referință al metodei în Java, este folosit pentru a apela o metodă prin referire la ea cu ajutorul clasei sale direct. Ele se comportă exact ca expresiile lambda. Singura diferență pe care o are față de expresiile lambda este că aceasta folosește referire directă la metodă prin nume în loc să ofere un delegat la metodă.

Sintaxă:

 ::>

Exemplu: Pentru a imprima toate elementele fluxului:

• Folosind expresia Lambda:

  stream.forEach( s->System.out.println(s));>

  Program:

  
  
  
  

  
  

  
  
  

  
  
  
  

  // Java code to print the elements of Stream> // without using double colon operator> > import> java.util.stream.*;> > class> GFG {> >public> static> void> main(String[] args)> >{> > >// Get the stream> >Stream stream> >= Stream.of(>'Geeks'>,>'For'>,> >'Geeks'>,>'A'>,> >'Computer'>,> >'Portal'>);> > >// Print the stream> >stream.forEach(s ->Printlns.out.system(e));>>> }> }>

  >

  >

  Ieșire:

  c++ int la șir

   Geeks For Geeks A Computer Portal>

• Folosind operatorul două puncte:

  stream.forEach( System.out::println);>

  Program: Pentru a demonstra utilizarea operatorului dublu două puncte

  
  

  
  
  

  // Java code to print the elements of Stream> // using double colon operator> > import> java.util.stream.*;> > class> GFG {> >public> static> void> main(String[] args)> >{> > >// Get the stream> >Stream stream> >= Stream.of(>'Geeks'>,>'For'>,> >'Geeks'>,>'A'>,> >'Computer'>,> >'Portal'>);> > >// Print the stream> >// using double colon operator> >stream.forEach(System.out::println);> >}> }>

  >

  >

  Ieșire:

   Geeks For Geeks A Computer Portal>

Când și cum să utilizați operatorul două puncte?

Referința metodei sau operatorul două puncte pot fi utilizate pentru a face referire:

• o metodă statică,
• o metodă de instanță sau
• un constructor.

Cum să utilizați referința de metodă în Java:

1. Metoda statica

   Sintaxă:

   (ClassName::methodName)>

   Exemplu:

   SomeClass::someStaticMethod>

   Program:

   
   

   
   
   

   // Java code to show use of double colon operator> // for static methods> > import> java.util.*;> > class> GFG {> > >// static function to be called> >static> void> someFunction(String s)> >{> >System.out.println(s);> >}> > >public> static> void> main(String[] args)> >{> > >List list =>new> ArrayList();> >list.add(>'Geeks'>);> >list.add(>'For'>);> >list.add(>'GEEKS'>);> > >// call the static method> >// using double colon operator> >list.forEach(GFG::someFunction);> >}> }>

   matrice de octeți în șir de caractere java

   >

   ls comandă Linux

   >

   Ieșire:

    Geeks For GEEKS>

2. Metoda de instanță

   Sintaxă:

   (objectOfClass::methodName)>

   Exemplu:

   System.out::println>

   Program:

   
   

   
   
   

   // Java code to show use of double colon operator> // for instance methods> > import> java.util.*;> > class> GFG {> > >// instance function to be called> >void> someFunction(String s)> >{> >System.out.println(s);> >}> > >public> static> void> main(String[] args)> >{> > >List list =>new> ArrayList();> >list.add(>'Geeks'>);> >list.add(>'For'>);> >list.add(>'GEEKS'>);> > >// call the instance method> >// using double colon operator> >list.forEach((>new> GFG())::someFunction);> >}> }>

   >

   >

   Ieșire:

    Geeks For GEEKS>

3. Super metoda

   Sintaxă:

   (super::methodName)>

   Exemplu:

   super::someSuperClassMethod>

   Program:

   
   

   
   
   

   // Java code to show use of double colon operator> // for super methods> > import> java.util.*;> import> java.util.function.*;> > class> Test {> > >// super function to be called> >String print(String str)> >{> >return> (>'Hello '> + str +>' '>);> >}> }> > class> GFG>extends> Test {> > >// instance method to override super method> >@Override> >String print(String s)> >{> > >// call the super method> >// using double colon operator> >Function> >func =>super>::print;> > >String newValue = func.apply(s);> >newValue +=>'Bye '> + s +>' '>;> >System.out.println(newValue);> > >return> newValue;> >}> > >// Driver code> >public> static> void> main(String[] args)> >{> > >List list =>new> ArrayList();> >list.add(>'Geeks'>);> >list.add(>'For'>);> >list.add(>'GEEKS'>);> > >// call the instance method> >// using double colon operator> >list.forEach(>new> GFG()::print);> >}> }>

   >

   >

   Ieșire:

    Hello Geeks Bye Geeks Hello For Bye For Hello GEEKS Bye GEEKS>

4. Metoda de instanță a unui obiect arbitrar de un anumit tip

   Sintaxă:

   (ClassName::methodName)>

   Exemplu:

   SomeClass::someInstanceMethod>

   Program:

   permanent

   
   

   
   
   

   // Java code to show use of double colon operator> // for instance method of arbitrary type> > import> java.util.*;> > class> Test {> >String str=>null>;> >Test(String s)> >{> >this>.str=s;> >}> >// instance function to be called> >void> someFunction()> >{> >System.out.println(>this>.str);> >}> }> > class> GFG {> > >public> static> void> main(String[] args)> >{> > >List list =>new> ArrayList();> >list.add(>new> Test(>'Geeks'>));> >list.add(>new> Test(>'For'>));> >list.add(>new> Test(>'GEEKS'>));> > >// call the instance method> >// using double colon operator> >list.forEach(Test::someFunction);> >}> }>

   >

   >

   Ieșire:

    Geeks For GEEKS>

5. Constructor de clasă

   Sintaxă:

   (ClassName::new)>

   Exemplu:

   ArrayList::new>

   Program:

   
   

   
   
   

   // Java code to show use of double colon operator> // for class constructor> > import> java.util.*;> > class> GFG {> > >// Class constructor> >public> GFG(String s)> >{> >System.out.println(>'Hello '> + s);> >}> > >// Driver code> >public> static> void> main(String[] args)> >{> > >List list =>new> ArrayList();> >list.add(>'Geeks'>);> >list.add(>'For'>);> >list.add(>'GEEKS'>);> > >// call the class constructor> >// using double colon operator> >list.forEach(GFG::>new>);> >}> }>

   >

   >

   gimp înlocuiți culoarea

   Ieșire:

    Hello Geeks Hello For Hello GEEKS>