JAVA8 Learning Notes (ii)----three predefined interfaces

Overview of three function interfaces

The JDK pre-defines a number of function interfaces to avoid repeated user definitions. The most typical is Function:

@FunctionalInterface  Public Interface Function<t, r> {      R apply (T t);}

This interface represents a function that takes a parameter of type T and returns a return value of type R.

Another predefined function interface is called Consumer, and the only difference with function is that it has no return value.

@FunctionalInterface  Public Interface Consumer<t> {    void  accept (T-T);}

There is also a predicate, used to determine whether a condition is satisfied. It is often used for sieve filtering operations:

@FunctionalInterface  Public Interface Predicate<t> {    boolean  Test (T-t);}

In summary, a lambda expression is actually defined as an anonymous method, except that this method must conform to at least one function interface.

Basic Application Pojo

 Public class Emp {    privateint  empno;     Private String ename;     // getter|setter|tostring slightly     Public Static void printemp (emp emp) {        System.out.println ("empno:" +emp.getempno () + "\nename:" +emp.getename ());}    } 

Static list

Static list<emp> emps = arrays.aslist (        new emp (1, "yw"),        new emp (2, "YT") ),        new emp (3, "YP"),        new emp (4, "YC"));

predicate applications

@Test  Public void testpredicate () {    predicate<Emp> predicate = Emp-Emp.getempno () >1;      for (Emp e:emps)    {        if(Predicate.test (e))        {            emp.printemp (e);     }}}

Run

function application

@Test  Public void testfunction () {    // extract name of employee    function<emp,string> Function = Emp  Emp.getename ();      for (Emp emp:emps)    {        = function.apply (EMP);        System.out.println (ename);    }}

Run

Consumer applications

@Test  Public void Testconsumer () {    Consumer<Emp> Consumer = Emp::p rintemp;      for (Emp e:emps)    {        consumer.accept (e);    }}

Run

Comprehensive application of preprocessing functions

Private void printEmpNameWhenEmpNoLg1 (iterable<t> source,predicate<t> predicate,function<t,r> function,                                            Consumer<R> Consumer) {    for(T t:source)    {        if( Predicate.test (t))        {            = function.apply (t);            Consumer.accept (R);}}    }

This function contains four parameters, respectively, for the list (in this case, Emps) and three predefined function interfaces that implement the Iterable interface. The application is as follows:

@Test  Public void Testfunctioninterface () {    predicate<Emp> predicate = Emp-Emp.getempno () >1;    function<Emp,String> function = Emp -emp.getename ();    Consumer<String> Consumer = system.out::p rintln;    PRINTEMPNAMEWHENEMPNOLG1 (Emps,predicate,function,consumer);}

Run

JAVA8 Learning Notes (ii)----three predefined interfaces