基础—四种函数式接口.java

import java.util.function.*;
import java.util.*;

class TestClass {
	public static void main(String[] args) {
		// 匿名内部类、lambda表达式、方法引用
		
		accept(200, (x) -> System.out.println(x));
		
		Random r = new Random();
		List<Integer> li = get(3, () -> r.nextInt(10));
		li.forEach(x->System.out.println(x));
		
		System.out.println(func("abc", n -> n.substring(0,1)));
		System.out.println(func("bca", new Function<String, String>(){
			@Override
			public String apply(String s){
				return s.substring(0,1);
			}
		}));
		System.out.println(func("ab c ", n -> n.trim()));
		
		List<Integer> fli = filterInt(li, x -> (x > 5));
		System.out.println(li);
		System.out.println(fli);
		
		// 当要传递给Lambada的操作，已经有实现的方法，可以使用方法引用 操作符 ::
		// 对象::实例方法
		// 类::静态方法
		// 类::实例方法
		Consumer<String> c1 = System.out::println;
		c1 = (x) -> System.out.println(x);
		c1.accept("str");
		Comparator<Integer> c2 = (x, y) -> Integer.compare(x, y);
		c2 = Integer::compare;
		System.out.println(c2.compare(1, 4));
		
		BiPredicate<String,String> c3 = (x, y) -> x.equals(y);
		c3 = String::equals;
		System.out.println(c3.test("11", "11"));
		
		
		// 构造器引用与函数式接口相结合，自动与函数式接口方法兼容 操作符 ClassName::new
		Supplier<User> u1 = User::new;
		u1 = () -> new User();
		System.out.println(u1.get());
		
		Function<String, User> u2 = (x) -> new User(x);
		u2 = User::new;
		System.out.println(u2.apply("小虎"));
		
		
		Function<Integer, String[]> f= String[]::new;
		System.out.println(f.apply(10).length);
		
	}
	
	// 1、Consumer 消费型接口
	static void accept(double c, Consumer<Double> x){
		x.accept(c);
	}
	
	// 2、Supplier 供给型接口 相当于容器
	static List<Integer> get(int n, Supplier<Integer> s1){
		List<Integer> li = new ArrayList<Integer>();
		for (int i = 0; i < n; i++) {
			li.add(s1.get());
		}
		return li;
	}
	
	// 3、Function 函数型接口
	static String func(String s, Function<String, String> fun){
		return fun.apply(s);
	}
	
	// 4、Predicate 断言型接口
	static List<Integer> filterInt(List<Integer> li, Predicate<Integer> p){
		List<Integer> l = new ArrayList<Integer>();
		for(Integer integer : li){
			if(p.test(integer)){
				l.add(integer); 
			}
		}
		return l;
	}
}

class User{
	
	String name;
	
	public User(){
		
	}
	
	public User(String name){
		this.name = name;
	}
	
	public String getName(){
		return this.name;
	}
	
	public void setName(String name){
		this.name = name;
	}
	
	public String toString(){
		return "user: [name: " + this.getName() + " ]";
	}
}