java8 流操作

1  合并多个流

    //合并多个流 
    private void merge() {
        List<String> list = new ArrayList<String>();
        list.add("I am a boy");
        list.add("I love the girl");
        list.add("But the girl loves another girl");
        
        List<String> result = list.stream() //得到流
        .map(line->line.split(" "))  //将每个元素转成String[]
        .flatMap(Arrays::stream)    //将每个String[] 转成流 ，并合并为一个大流
        .distinct()    //对元素去重
        .collect(Collectors.toList());   //终止流得到集合
         result.forEach(System.out::println);   //打印
    }

2  是否匹配任一元素

    //是否匹配任一元素
    private void anyMatch() {
    
        List<Person> persons = Arrays.asList(new Person("zhangsan", 18),new Person("lisi", 19));
        boolean isHas = persons.stream().anyMatch(e -> e.getAge() == 18);
        System.out.println("isHas : "+isHas);
    }

3  是否所有元素都匹配

    //是否所有元素都匹配
    private void allMatch() {
    
        List<Person> persons = Arrays.asList(new Person("zhangsan", 18),new Person("lisi", 19));
        boolean bool = persons.stream().allMatch(e -> e.getAge() == 18);
        System.out.println("isHas : "+bool);
    }

4  是否所有元素都不匹配

    //是否所有元素都不匹配
    private void  noneMatch() {
    
        List<Person> persons = Arrays.asList(new Person("zhangsan", 18),new Person("lisi", 19));
        boolean bool = persons.stream().noneMatch(e -> e.getAge() == 20);
        System.out.println("isHas : "+bool);
    }

 5 新增容器optional  (存储一个对象或者不存，可以避免空指针异常)

    private void  findFirst() {
    
        List<Person> persons = Arrays.asList(new Person("zhangsan", 18),new Person("lisi", 19));
        Optional<Person>  optional = persons.stream().findFirst();
        System.out.println(optional.get().getName());
        
    }

6  归并  reduce

    //归并
    private void  testReduce() {
        List<Person> persons = Arrays.asList(new Person("zhangsan", 18),new Person("lisi", 19));
        //reduce 不设置初始值
        Optional<Integer> optional = persons.stream().map(e -> e.getAge()).reduce((a,b) -> a + b);
        System.out.println(optional.get());
        //reduce 设置初始值
        Integer ageTotal = persons.stream().map(e -> e.getAge()).reduce(0,(a,b) -> a + b);
        System.out.println(ageTotal);
    }