Operator două puncte (::) în Java
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: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:
- 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);>>}>}>
Ieșire:Geeks For GEEKS
- 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
- 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
- Metoda de instanță a unui obiect arbitrar de un anumit tip
Sintaxă:
(ClassName::methodName)
Exemplu:
SomeClass::someInstanceMethod
Program:
// 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
- 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>);>>}>}>
Ieșire:Hello Geeks Hello For Hello GEEKS
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