初识stream流-526互联

下面是stream的 filter 和 forEach 的使用

filter 来过滤出满足条件的元素

forEach 逐一处理流中的元素

import java.util.ArrayList;
import java.util.List;
 
public class Demo2Steam {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("张无忌");
        list.add("周芷若");
        list.add("赵敏");
        list.add("小昭");
        list.add("殷离");
        list.add("张三");
        list.add("张三丰");
        list.stream()
                .filter(name -> name.startsWith("张"))
                .filter(name -> name.length() == 3)
                .forEach(name -> System.out.println(name));
    }
}

anyMatch : 遍历流,判断集合里面元素是否有符合条件的数据,有就返回true

 boolean anyMatch = list.stream().anyMatch(x -> x > 6);
        
 System.out.println("是否存在大于6的值：" + anyMatch);

allMatch : 遍历流,判断集合里面元素是否都符合条件的数据,全部符合就返回true

boolean flag = folderFileList.stream().allMatch(folderFile -> StringUtils.isNotEmpty(folderFile.getFileUrl()));

map(Person::getName) : 获取符合的字段

collect:把流数据收集到集合当中

public class StreamTest {
    public static void main(String[] args) {
        List<Person> personList = new ArrayList<Person>();
        personList.add(new Person("Tom", 8900, 23, "male", "New York"));
        personList.add(new Person("Jack", 7000, 25, "male", "Washington"));
        personList.add(new Person("Lily", 7800, 21, "female", "Washington"));
        personList.add(new Person("Anni", 8200, 24, "female", "New York"));
        personList.add(new Person("Owen", 9500, 25, "male", "New York"));
        personList.add(new Person("Alisa", 7900, 26, "female", "New York"));

        List<String> fiterList = personList.stream().filter(x -> x.getSalary() > 8000).map(Person::getName)
                .collect(Collectors.toList());
        System.out.print("高于8000的员工姓名：" + fiterList);
    }
}

聚合（max、min、count）

public class StreamTest {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("adnm", "admmt", "pot", "xbangd", "weoujgsd");

        Optional<String> max = list.stream().max(Comparator.comparing(String::length));
        System.out.println("最长的字符串：" + max.get());
    }
}

public class StreamTest {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(7, 6, 9, 4, 11, 6);

        // 自然排序
        Optional<Integer> max = list.stream().max(Integer::compareTo);
        System.out.println("自然排序的最大值：" + max.get());
    
    }
}

public class StreamTest {
    public static void main(String[] args) {
        List<Person> personList = new ArrayList<Person>();
        personList.add(new Person("Tom", 8900, 23, "male", "New York"));
        personList.add(new Person("Jack", 7000, 25, "male", "Washington"));
        personList.add(new Person("Lily", 7800, 21, "female", "Washington"));
        personList.add(new Person("Anni", 8200, 24, "female", "New York"));
        personList.add(new Person("Owen", 9500, 25, "male", "New York"));
        personList.add(new Person("Alisa", 7900, 26, "female", "New York"));

        Optional<Person> max = personList.stream().max(Comparator.comparingInt(Person::getSalary));
        System.out.println("员工工资最大值：" + max.get().getSalary());
    }
}

英文字符串数组的元素全部改为大写。整数数组每个元素+3。

public class StreamTest {
    public static void main(String[] args) {
        String[] strArr = { "abcd", "bcdd", "defde", "fTr" };
        List<String> strList = Arrays.stream(strArr).map(String::toUpperCase).collect(Collectors.toList());

        List<Integer> intList = Arrays.asList(1, 3, 5, 7, 9, 11);
        List<Integer> intListNew = intList.stream().map(x -> x + 3).collect(Collectors.toList());

        System.out.println("每个元素大写：" + strList);
        System.out.println("每个元素+3：" + intListNew);
    }
}