jdk1.8 Java函數式編程示例:Lambda函數/方法引用/4種內建函數式接口(功能性-/消費型/供給型/斷言型)

package unittest;

import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;

@FunctionalInterface
interface IFuction1

{
public abstract P uppCase();
}
@FunctionalInterface
interface IFuction2

{
public abstract P uppCase(P p);
}
@FunctionalInterface
interface IFuction3<P,R>{
public abstract R trans(P p);
}
public class TestLocal{
public static void main(String[] args) {
//利用方法引用的概念可以位一個方法定義多個名字,但是要求必須是函數式接口.

	IFuction1<String> ifunction1  = "avc" :: toUpperCase;//    public String toUpperCase() {
	String str1 = ifunction1.uppCase();//實例對象::普通方法(不帶參數)
	System.out.println(str1);
	
	IFuction2<String> ifunction2  = String :: toUpperCase; //    public String toUpperCase() {
	String str2 = ifunction2.uppCase("avc");//類名稱::普通方法(帶參數)
	System.out.println(str2);
	
	IFuction3<Integer,String> ifunction3  = String :: valueOf;//類名稱::static方法(帶參數) //    public static String valueOf(int i) {
	String str3 = ifunction3.trans(123456);
	System.out.println(str3.length());
	//內建函數式接口
	//1.功能型內建函數式接口:有參數 有返回值
	Function<String,Boolean> fun = "abc123"::startsWith;
	System.out.println("1功能型內建函數式接口:" + fun.apply("abc"));
	
	//2.消費型內建函數式接口:有參數 無返回值
	Consumer<String> con = System.out::println;
	con.accept("2消費型內建函數式接口:avc");
	//3.供給型內建函數式接口:無參數 有返回值
	Supplier<String> supplier = "abc"::toUpperCase;
	System.out.println("3供給型內建函數式接口:" + supplier.get());
	//4.斷言型內建函數式接口:無參數 有返回值
	Predicate<String> predicate = String::isEmpty;
	System.out.println("4斷言型內建函數式接口:" + predicate.test("a"));
	
	Predicate<String> fun_predicate = "abc123"::startsWith;
	System.out.println("5功能_斷言型內建函數式接口:" + fun_predicate.test("abc"));
}

}