Java中的内置功能接口是什么？
java.util.function包定义了几个我正内置功能接口可以在创建时使用lambda表达式或方法的引用。
内置功能接口：
1）功能接口
功能接口仅具有一个单一的方法应用()。它可以接受任何数据类型的对象，并返回任何数据类型的结果。
示例
import java.util.*;
import java.util.function.*;
public class FunctionTest {
public static void main(String args[]) {
String[] countries = {"India", "Australia", "England", "South Africa", "Srilanka", "Newzealand", "West Indies", "Scotland"};
Function<String[], String> converter = (all) -> { // lambda expression
String names = "";
for(String n : all) {
String result = n.substring(0, n.indexOf(""));
result = n.substring(n.indexOf("")) + " " + result;
names += result + "\n";
}
return names;
};
System.out.println(converter.apply(countries));
}
}输出结果
India Australia England South Africa Srilanka Newzealand West Indies Scotland
2）供应商接口
一个 供应商接口只有一个单一的方法调用，get()方法。它不接受任何参数，并返回任何数据类型的对象。
示例
import java.util.*;
import java.util.function.*;
public class SupplierTest {
private static void printNames(Supplier<String> arg) {
System.out.println(arg.get());
}
private static void listBeginWith(List<String> list, Predicate<String> valid) {
printNames(() -> "\nList of countries:");
list.forEach(country -> { // lambda expression
if(valid.test(country)) {
printNames(() -> country);
}
});
}
public static void main(String[] args) {
String[] countries = {"India", "Australia", "England", "South Africa", "Srilanka", "Newzealand", "West Indies"};
List<String> countryList = Arrays.asList(countries);
listBeginWith(countryList, (s) -> s.startsWith("I"));
listBeginWith(countryList, (s) -> s.contains("I"));
listBeginWith(countryList, (s) -> s.endsWith("ia"));
}
}输出结果
List of countries: India List of countries: India West Indies List of countries: India Australia
3）用户接口
该用户接口只有一个单一的方法称为accept()方法。它接受任何数据类型的单个参数，并且不返回任何结果。
示例
import java.util.*;
import java.util.function.*;
public class ConsumerTest {
public static void main(String[] args) {
String[] countries = {"India", "Australia", "England", "South Africa", "Srilanka", "Newzealand", "West Indies"};
System.out.print("The list of countries:\n"); Arrays.asList(countries).forEach((country) -> System.out.println(country)); // lambda expression
}
}输出结果
The list of countries: India Australia England South Africa Srilanka Newzealand West Indies
4）谓词接口
谓词接口 仅具有一个单一的方法 测试()。取决于其变量的值，它可以是对 或错 。
示例
import java.util.*;
import java.util.function.*;
public class PredicateTest {
private static List getBeginWith(List<String> list, Predicate<String> valid) {
List<String> selected = new ArrayList<>();
list.forEach(country -> { // lambda expression
if(valid.test(country)) {
selected.add(country);
}
});
return selected;
}
public static void main(String[] args) {
String[] countries = {"India", "Australia", "England", "South Africa", "Srilanka", "Newzealand", "West Indies"};
List<String> countryList = Arrays.asList(countries);
System.out.println(getBeginWith(countryList, (s) -> s.startsWith("A")));
System.out.println(getBeginWith(countryList, (s) -> s.contains("W")));
System.out.println(getBeginWith(countryList, (s) -> s.endsWith("nd")));
}
}输出结果
[Australia] [West Indies] [England, Newzealand]