java8-使用函数式接口

使用函数式接口

Predicate

@FunctionalInterface
interface Predicate{
    boolean test(T t);
}

public static  List filter(List list,Predicate p){
        List ts = new ArrayList<>();
        for (T t : list) {
            if (p.test(t)) {
                ts.add(t);
            }
        }
        return ts;
}

Consumer

@FunctionalInterface
public interface Consumer {  
    void accept(T t);
}

public static  void forEach(List list,Consumer c) {
        for (T t : list) {
            c.accept(t);
        }
}

public static void main(String[] args) {
  forEach(Arrays.asList(1,2,3,4,5),i-> System.out.println(i));

}

Function

@FunctionalInterface
public interface Function {
    R apply(T t);
}

public static  List map(List list, Function f) {
  List result = new ArrayList<>();
  for (T t : list) {
    result.add(f.apply(t));
  }
  return result;
}

public static void main(String[] args) {
  List map = map(Arrays.asList("lambdas", "in", "action"), s -> s.length());
  System.out.println(map);
}

Lambdas及函数式接口的例子

例子                                                                   对应接口
布尔表达式: (List list) -> list.isEmpty()                    Predicate>
创建对象:   () -> new Apple(10)                                     Supplier
消费一个对象:(Apple a) ->
   System.out.println(a.getWeight());                               Consumer
从一个对象中选择/提取:(String s )->s.length()                         Function或
                                                                    ToIntFunction
合并两个值:(int a, int b)->a*b                                       IntBinaryOperator
比较两个对象:(Apple a1,Apple a2)->                        BiFunction
  a1.getWeight().compareTo(a2.getWeight())                      或ToIntBiFunction