IT工程師數位筆記本

// Function<T, R> -T作為輸入，返回的R作為輸出 
        Function<String,String> function = (x) -> {System.out.print(x+": ");return "Function";};
        System.out.println(function.apply("hello world"));
        
        //Predicate<T> -T作為輸入，返回的boolean值作為輸出 
        Predicate<String> pre = (x) ->{System.out.print(x);return false;};
        System.out.println(": "+pre.test("hello World"));
        
        //Consumer<T> - T作為輸入，執行某種動作但沒有返回值 
        Consumer<String> con = (x) -> {System.out.println(x);};
        con.accept("hello world");
        
        //Supplier<T> - 沒有任何輸入，返回T 
        Supplier<String> supp = () -> {return "Supplier";};
        System.out.println(supp.get());
        
        //BinaryOperator<T> -兩個T作為輸入，返回一個T作為輸出，對于“reduce”操作很有用 
        BinaryOperator<String> bina = (x,y) ->{System.out.print(x+" "+y);return "BinaryOperator";};
        System.out.println("  "+bina.apply("hello ","world"));

hello world: Function
hello World: false
hello world
Supplier
hello  world  BinaryOperator

import java.time.Instant;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.stream.IntStream;

public class Test {

    public static void main(String ... args) throws Exception{
        //1:lambda表達式和功能接口
        Add a = (x, y) -> x+y;
        System.out.println(a.add(100,200));
        System.out.println("------------------------------------------1");
        //2:lambda表達式和集合
        List<String> list = Arrays.asList("aaa","bbbb","cccc");
        list.forEach(e -> {System.out.println(e);});
        System.out.println("------------------------------------------2");
        //3:接口中可以包含靜態方法
        Add.interfaceStaticMethod();
        System.out.println("------------------------------------------3");
        //4:接口中可以包含默認方法，默認方法實現類并不是必須實現。
        Add add = (x,y) -> x-y;
        add.defaultMethod();
        System.out.println("------------------------------------------4");
        //5:java.util.function 包下提供的函數式接口
        String s = "hello";
        Function<String,String> function = x -> x+" world";
        System.out.println(function.apply(s));
        System.out.println("------------------------------------------5");
        //6:java.util.stream包
        List<Integer> strings = Arrays.asList(1,2,3); 
        IntStream stream = strings.stream().mapToInt(Integer::valueOf);
        stream.forEach(x->{System.out.println(x);});
        
        System.out.println("------------------------------------------6");
        System.out.println(Instant.now().getNano());
        System.out.println(Instant.MIN);
        System.out.println(Instant.MAX);
    }
    
}

@FunctionalInterface    //函數式接口（也叫功能接口），此接口中只能有一個抽象方法。函數式接口可以用lambda表達式實例化。
interface Add {
    public int add(int x,int y);
    public static void interfaceStaticMethod(){
        System.out.println("interface static method");
    }
    public default void defaultMethod(){
        System.out.println("default method");
    }
    
}

300
------------------------------------------1
aaa
bbbb
cccc
------------------------------------------2
interface static method
------------------------------------------3
default method
------------------------------------------4
hello world
------------------------------------------5
1
2
3
------------------------------------------6
280000000
-1000000000-01-01T00:00:00Z
+1000000000-12-31T23:59:59.999999999Z