Lambda 表达式方法引用

2018-01-11

Lambda 可以使用现成已经实现的方法。

要求被调用的方法的参数类型和返回值和 Lambda 表达式中函数接口中抽象方法的参数类型和返回值一致

对象::实例方法名

Consumer<String> consumer = x -> System.out.println(x);
		
PrintStream printStream = System.out;
Consumer<String> consumer1 = printStream::print;

1
2
3

Consumer<String> consumer = x -> System.out.println(x);
		
Consumer<String> consumer1 = System.out::print;

类::静态方法名

Comparator<Integer> comparator = (x, y) -> Integer.compare(x, y);
comparator.compare(2,3);
	
Comparator<Integer> comparator1 = Integer::compare;
comparator1.compare(3,4);

类::实例方法名

要求第一个参数是实例方法的调用者，第二个参数是实例方法的参数

BiPredicate<String, String> biPredicate = (x, y) -> x.equals(y);
biPredicate.test("b", "b");
	
BiPredicate<String, String> biPredicate1 = String::equals;
biPredicate1.test("b", "b");

构造函数引用

可以自动匹配对应的构造函数

Supplier<String> supplier = () -> new String();
System.out.println(supplier);
	
Supplier<String> supplier1 = String::new;
System.out.println(supplier1.get());

Function<String, String> function = (x) -> new String(x);
System.out.println(function.apply("a"));
	
Function<String, String> function1 = String::new;
System.out.println(function1.apply("b"));

数组引用

Function<Integer, String[]> function = (x) -> new String[x];
System.out.println(function.apply(5).length);
	
Function<Integer, String[]> function1 = String[]::new;
System.out.println(function1.apply(6).length);

代码可参考lxmuse-jdk8-new-feature-lambda-04