Guava Learning--function, predicate

function is used for synchronous transformations.

predicate is used for filtering.

Import java.util.Collection;

Import Java.util.Iterator;

Import java.util.List;

Import Java.util.Map;

Import com.google.common.base.Function;

Import com.google.common.base.Functions;

Import com.google.common.base.Objects;

Import Com.google.common.base.Predicate;

Import Com.google.common.collect.Collections2;

Import com.google.common.collect.Iterators;

Import com.google.common.collect.Lists;

Import Com.google.common.collect.Maps;

Public class User {

private String username;

private String sex;

Public User (string username, string sex) {

This . Username = username;

This . sex = sex;

}

void Setusername (String username) {

This . Username = username;

}

void Setsex (String sex) {

This . sex = sex;

}

String GetUserName () {

return username;

}

String Getsex () {

return sex;

}

@Override

Public String toString () {

return Objects.tostringhelper (this). Omitnullvalues (). Add ("username", username). Add ("Sex" , Sex). ToString ();

}

public static void Main (string[] args) {

user u1 = New User ("Malone", "man");

user U2 = New User ("Lanlan", "woman");

list<user> List = lists.newarraylist (u1, U2);

//Function here for type conversion

collection<string> result = Collections2.transform (list, new Function<user, string> ( ) {

@Override

Public String apply (user user) {

if (objects.equal (user, null)) {

return "";

}

return user.tostring ();

}

});

For (String SS: result) {

System. OUT.PRINTLN (ss);

}

//predicate here is for filtering

collection<user> resultuser = collections2.filter (list, new predicate<user> () {

@Override

Public boolean apply (user user) {

if (objects.equal (user, null)) {

return false;

}

if (objects.equal (user.getsex (), "Woman")) {

return false;

}

return true;

}

});

For (User SS: resultuser) {

System. OUT.PRINTLN (ss);

}

Function<user, string> f1 = new Function<user, string> () {

@Override

Public String apply (user user) {

if (objects.equal (user, null)) {

return "";

}

return user.getusername ();

}

};

//Multiple tool classes can be programmed using class-function

collection<string> result1 = collections2.transform (list, F1);

For (String SS: result1) {

System. Out.println ("1:" + ss);

}

list<string> strlist = Lists.transform (List, F1);

For (String SS: strlist) {

System. Out.println ("2:" + ss);

}

iterator<string> it = iterators.transform (list.iterator (), F1);

While (it.hasnext ()) {

System. Out.println ("3:" + It.next ());

}

function<string, string> f2 = new function<string, string> () {

@Override

Public string Apply (string input) {

if (objects.equal (input, "Malone")) {

return "Malone s function";

} else {

return "Lanlan s function";

}

}

};

//Connect multiple function

Warning: Here the parameter position of the compose method cannot be reversed,

* Function<a, c> compose (Function<b, c> G, Function<a,? extends b> f)

* Incoming function<b,c>, function<a,? Extends b> group synthesis Function<a, c>

Function<user, string> f3 = Functions.compose (f2, F1);

list<string> mylist = Lists.transform (List, F3);

System. out.println (mylist.get (0));

map<string, string> Map = Maps.newhashmap ();

map.put ("1", "2");

//functions can convert a map, make the code more straightforward, and provide default value support

function<string, string> lookup = functions.formap (map, "default value");

System. out.println (lookup.apply ("1"));

}

}

Guava Learning--function, predicate