使用函数式接口

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

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

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

public static <T> void forEach(List<T> list,Consumer<T> 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));

}

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

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

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

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