【Java8新特性】——四大内置核心函数式接口

       之前其实写过Java8新特性的函数式接口的文章，现在再一次重复，之前学过的内容，偏重于笔记，在工作中的使用场景并不是很多，再一次总结，除了温故而知新，也结合一些自己工作中遇到的案例，希望可以帮助到需要的朋友。

1、消费型接口，有入参，没有返回值

通常用于对入参的逻辑处理，简化重复定义方法的流程，优化代码简洁度。

@FunctionalInterface
public interface Consumer {

    /**
     * Performs this operation on the given argument.
     *
     * @param t the input argument
     */
    void accept(T t);

    /**
     * Returns a composed {@code Consumer} that performs, in sequence, this
     * operation followed by the {@code after} operation. If performing either
     * operation throws an exception, it is relayed to the caller of the
     * composed operation.  If performing this operation throws an exception,
     * the {@code after} operation will not be performed.
     *
     * @param after the operation to perform after this operation
     * @return a composed {@code Consumer} that performs in sequence this
     * operation followed by the {@code after} operation
     * @throws NullPointerException if {@code after} is null
     */
    default Consumer andThen(Consumer after) {
        Objects.requireNonNull(after);
        return (T t) -> { accept(t); after.accept(t); };
    }
}

你如果需要访问类型T的对象，并对其执行某些操作，就可以使用这个接口。而且此接口还有默认方法andThen，用于拼接多个Consumer对象的执行内容。按拼接顺序从前往后依次执行

@Test
    public void test() {
        happy(1000, x -> System.out.println(x));
    }

    private void happy(Integer money, Consumer consumer) {
        consumer.accept(money);
        consumer.andThen(x -> System.out.println(x / 2)).accept(money);
    }

2、供给型接口，没有入参，只有返回值

它接受一个泛型T的对象，并返回这个泛型T的对象

@FunctionalInterface
public interface Supplier {

    /**
     * Gets a result.
     *
     * @return a result
     */
    T get();
}

eg 生成10个数字，作为list返回 

public List getList(int num, Supplier supplier) {
        List list = Lists.newArrayList();
        for (int i = 0; i < num; i++) {
            list.add(supplier.get());
        }
        return list;
    }
@Test
    public void test() {
        List list = getList(10, () -> (int) (Math.random() * 100));
        System.out.println(list);
    }

3、函数型接口，一个参数，有返回值

它接受一个泛型T的对象，并返回一个泛型R的对象，将输入对象的信息映射到输出，可以使用此接口。

@FunctionalInterface
public interface Function {

    /**
     * Applies this function to the given argument.
     *
     * @param t the function argument
     * @return the function result
     */
    R apply(T t);
}

public String strHandler(Integer x, Function function) {
        return function.apply(x);
    }

    @Test
    public void test1() {
        String handler = strHandler(1, x -> "我有" + x + "个朋友");
        System.out.println(handler);
    }

举个工作中简化代码的逻辑

优化前

//只有输入参数不同，其他的都是重复逻辑
//呼入总量
            Map callCityMap = callList.stream()
                    .collect(Collectors.groupingBy(WorkOrder::getCity, Collectors.counting()));
            //呼入有效咨询量
            Map callValidCityMap = callValidList.stream()
                    .collect(Collectors.groupingBy(WorkOrder::getCity, Collectors.counting()));
            //呼入分配量
            Map callAppointCityMap = callAppointList.stream()
                    .collect(Collectors.groupingBy(WorkOrder::getCity, Collectors.counting()));
            //在线咨询
            Map onlineCityMap = onlineList.stream()
                    .collect(Collectors.groupingBy(WorkOrder::getCity, Collectors.counting()));

优化之后

private Map getWorkCount(List workOrders,Function, Map> function){
    return function.apply(workOrders);
}

Function, Map> function = workOrders -> workOrders.stream().collect(Collectors.groupingBy(WorkOrder::getSeatCode, Collectors.counting()));

Map callCityMap =getWorkCount(callList,function);

Map callSeatMap =getWorkCount(callSeatList,function);

4、断言型接口 有参数，返回值为boolean

@FunctionalInterface
public interface Predicate {

    /**
     * Evaluates this predicate on the given argument.
     *
     * @param t the input argument
     * @return {@code true} if the input argument matches the predicate,
     * otherwise {@code false}
     */
    boolean test(T t);
}

举例说明 对字符串的过滤可以进行筛选 

 @Test
    public void test2() {
        boolean result = judgeLength("iiiiii", s -> s.length() > 2);
        System.out.println(result);
    }

    public boolean judgeLength(String s, Predicate predicate) {
        return predicate.test(s);
    }

举个工作中简化代码的逻辑

//只有filter中内容不一样
List callList = workOrderList.stream()
                .filter(workOrder -> workOrder.getActivityType() == EActivityType.CALL.getValue())
                .collect(Collectors.toList());

        List callValidList = workOrderList.stream()
                .filter(workOrder -> workOrder.getActivityType() == EActivityType.CALL.getValue()
                        && resourceType.contains(workOrder.getServiceCode()))
                .collect(Collectors.toList());

        List callAppointList = workOrderList.stream()
                .filter(workOrder -> workOrder.getChannelType() != null && workOrder.getChannelType() == EActivityType.CALL.getValue()
                        && workOrder.getAppointResult() != null && workOrder.getAppointResult() == EAppointResult.ADVISER.getValue())
                .collect(Collectors.toList());

        List onlineList = workOrderList.stream()
                .filter(workOrder -> workOrder.getActivityType() == EActivityType.ONLINE.getValue())
                .collect(Collectors.toList());

优化后,将过滤部分利用断言接口抽象，减少冗余代码

private List  getWorkList(List workOrderList, Predicate call) {
        List collect = workOrderList.stream().filter(call).collect(Collectors.toList());
        return collect;
    }
Predicate call = workOrder -> workOrder.getActivityType()== EActivityType.CALL.getValue();
List collect= getWorkList(workOrderList, call);

总结

        java8带来的好处就是简化现在的冗余代码，但是很多知识学过后特别容易忘记，温故知新，遇到冗余的地方要想办法去解决，尽量将学习的内容在工作中得已实践。

       岁月正好，吾辈还需更加努力。