A method reference to a Java 8 lambda expression:: double-colon operator

The double-colon operator is a method reference in Java, and the method references the format of the class Name:: Method name.

This is only the method name, and the method name is not followed by the parentheses "()". --------> Such a formula does not necessarily call this method. This is generally used as a lambda expression, and lambda has the so-called lazy load, not parentheses that is, to see how the method is invoked.

For example:

An expression:

Person->person.getage ();

can be replaced by

Person::getage

An expression:

(), New hashmap<> ();

can be replaced by

Hashmap::new

This method refers to or is a double-colon operation that corresponds to a parameter type of function<t,r>t that represents the passed-in type and R for the returned type. For example, the expression person--person.getage (), the passed parameter is person, the return value is Peron.getage (), then the method reference Person::getage

Corresponds to the funciton<person,integer> type.

Example code: Capitalize all the strings inside the list<string> and return to the new Arraylist<string>, as in the previous example.

@Testpublic void Converttest () {    list<string> collected = new arraylist<> ();    Collected.add ("alpha");    Collected.add ("beta");    collected = Collected.stream (). Map (String, String.touppercase ()). Collect (Collectors.tolist ());    SYSTEM.OUT.PRINTLN (collected);      }

The following form is programmed after using the double-colon operator:

@Testpublic void Testconvertest () {     list<string> collected = new arraylist<> ();     Collected.add ("alpha");     Collected.add ("beta");     collected = Collected.stream (). Map (String::touppercase). Collect (Collectors.tocollection (arraylist::new));    SYSTEM.OUT.PRINTLN (collected);     }

A method reference to a Java 8 lambda expression:: double-colon operator