Double colon (: :) use forms mainly comprising:
Class name :: instance methods
:: Object instance methods
Through the sample code below illustrates in detail.
Double colon (: :) function and arrows (->) collectively shown below:
Such as: HashMap :: new equivalent to () -> new HashMap ()
. 1 public class the Test { 2 . 3 // instance object references an instance method . 4 Supplier <String> supplier1 = "lowerCase" :: the toUpperCase; . 5 Supplier <String> supplier1_1 = () -> "lowerCase" .toUpperCase (); . 6 . 7 / / class reference (without parameters) constructor . 8 supplier2 Supplier :: = String <String> new new ; . 9 Supplier <String> supplier2_1 = () -> new new String (); 10 . 11 // class references (with parameters) constructor 12 Function <String, String> function1 :: = String new new ; 13 is Function <String, String> function1_1 = (String STR) -> new new String (STR); 14 15 // class reference instance method, the instance of the object passed as parameters, the parameters, the same parameter types 16 Function <String, String > = function2 String the toUpperCase ::; . 17 Function <String, String> function2_1 = (String STR) -> str.toUpperCase (); 18 is . 19 // the Predicate <T> be understood as a special Function <T, Boolean> 20 is 21 is Person = the Person new new the Person (); 22 is // shall no static method reference 23 is Supplier supplierBln = <Boolean> the Person :: isTest; 24 Supplier <Boolean> supplierBln_1 = () ->Person.isTest (); 25 26 is // instance object method call instance 27 Supplier <String> supplierStr = Person :: getName; 28 Supplier <String> supplierStr_1 = () -> person.getName (); 29 30 // no arguments The constructor 31 is Supplier <the Person> = supplierPerson the Person :: new new ; 32 Supplier <the Person> supplierPerson_1 = () -> new new the Person (); 33 is 34 is // there argument constructor 35 BiFunction <String, String, the Person> = the Person biFunction :: new new ; 36 BiFunction<String, String, Person> biFunction_1 = (name, gender) -> new Person(name, gender); 37 38 // 类名调用实例方法，入参为传入实例对象 39 Function<Person, Person> functionP = Person::toOpposite; 40 Function<Person, Person> functionP_1 = person -> person.toOpposite(); 41 42 Consumer<String> consumer = System.out::println; 43 Consumer<String> consumer_1 = (String str) -> System.out.println(str);; 44 45 public static void main(String[] args) { 46 List<String> list = Arrays.asList("1", "2", "3"); 47 boolean bl = list.stream().anyMatch("1"::equals); 48 List<String> retval = list.stream().collect(Collectors.toCollection(LinkedList::new)); 49 50 List<Person> persons = Arrays.asList(new Person(10, "Jack", "M")); 51 Person person = new Person(20, "Lily", "F"); 52 persons.stream().filter(Person::isMale).filter(person::isUnder).collect(Collectors.toCollection(ArrayList::new)); 53 } 54 }
Person class code as follows:
1 public class Person { 2 int age; 3 String name; 4 String gender; 5 6 public Person() { 7 } 8 9 public Person(String name) { 10 this.name = name; 11 } 12 13 public Person(String name, String gender) { 14 this.name = name; 15 this.gender = gender; 16 } 17 18 public Person(int age, String name, String gender) { 19 this.age = age; 20 this.name = name; 21 this.gender = gender; 22 } 23 24 public String getName() { 25 return this.name; 26 } 27 28 public Person toOpposite() { 29 if (gender.charAt(0) == 'M') 30 gender = "F"; 31 else 32 gender = "M"; 33 return this; 34 } 35 36 public static boolean isTest() { 37 return true; 38 } 39 40 public boolean isUnder(Person person) { 41 return person.age > this.age; 42 } 43 44 public boolean isMale() { 45 return gender.equals("M"); 46 } 47 }