java8新特性 Stream API 终止操作

Stream的终止操作：终止操作会从流的流水线生成结果，其结果可以是任何不适流的操作，例如：List,Integer,甚至是void

一，查找与匹配

 List<Employee> employeeList1 = Arrays.asList(
            new Employee("cdy1",18,1772.22),
            new Employee("cdy2",18,1872.22),
            new Employee("cdy3",18,1672.22),
            new Employee("cdy4",18,1972.22)
    );

    List<Employee> employeeList2 = Arrays.asList(
            new Employee("cdy1",18,1772.22),
            new Employee("cdy2",19,1872.22),
            new Employee("cdy3",11,1672.22),
            new Employee("cdy4",18,1972.22)
    );

说明：Predicate 是断言型函数式接口；

1、allMatch(Predicate p) 检查流中所有元素是否都满足条件，返回boolean值

    @Test
    public void test1(){
        boolean b1 = employeeList1.stream().allMatch((e) -> {
            if (e.getAge() == 18 || e.getSalary() == 1972.22) {
                return true;
            }
            return false;
        });
        System.out.println(b1);//truw
        boolean b2 = employeeList2.stream().allMatch((e) -> {
            if (e.getAge() == 18 || e.getSalary() == 1972.22) {
                return true;
            }
            return false;
        });
        System.out.println(b2); //false

    }

2、anyMatch(Predicate p) 检查所有元素中至少有一个元素满足条件

@Test
    public void test2() {
        boolean b = employeeList1.stream().anyMatch((e) -> e.getAge() == 18);
        System.out.println(b);//true
    }

3、noneMatch(Predicate p) 所有元素都不满足条件返回true，否则false

@Test
    public void test3() {
        boolean b = employeeList1.stream().noneMatch((e) -> e.getAge() == 0);
        System.out.println(b);//true
    }

4、findFirst() 返回第一个元素

@Test
    public void test4() {
        Optional<Employee> first = employeeList1.stream()
                                        .sorted((e1, e2) -> Double.compare(e1.getSalary(), e2.getSalary()))
                                        .findFirst();

        System.out.println(first.get().getSalary());//1672.22
    }

5、findAny() 返回当前流中的任意元素

 @Test
    public void test5() {
        Optional<Employee> any = employeeList1.stream().findAny();
        System.out.println(any.get().getSalary());//1772.22
    }

6.reduce(T iden, BinaryOperator b) (规约)可以将流中元素反复结合起来，得到一个值。返回 T

@Test
    public void test8() {
        List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5);
        Integer reduce = integers.stream().reduce(3, (x, y) -> x + y);
        System.out.println(reduce);

    }

7.collect(Collector c) 将流转换为其他形式。接收一个 Collector接口的 实现，用于给Stream中元素做汇总的方法

 

@Test
    public void test9() {
        List<Integer> collect = employeeList2.stream().map(Employee::getAge).collect(Collectors.toList());
        collect.forEach(System.out::println);

        Set<String> collect1 = employeeList2.stream().map(Employee::getName).collect(Collectors.toSet());
        collect1.forEach(System.out::print);

        employeeList2.stream().collect(Collectors.toCollection(HashSet::new));

    }