Java8新特性Stream之Collectors类型转换

系统管理员 2023-01-10 14:43 182阅读 0赞

# Java8新特性Stream之Collectors(toList()、toSet()、toCollection()、joining()、partitioningBy()、collectingAndT) #

将流中的数据转成集合类型：  
一、将数据收集进一个列表(Stream 转换为 List，允许重复值，有顺序)

package com.demo.stream.collectors;
    import java.util.List;
    import java.util.stream.Collectors;
    import java.util.stream.Stream;
    public class Demo1 {
        public static void main(String[] args) {
            //1.将数据收集进一个列表(Stream 转换为 List，允许重复值，有顺序)
            //创建流
            Stream<String> language = Stream.of("java", "python", "C++","php","java");
            List<String> listResult = language.collect(Collectors.toList());
            //forEach遍历输出
            listResult.forEach(System.out::println);
        }
    }
    package com.demo.stream.collectors;
    import java.util.Arrays;
    import java.util.List;
    import java.util.stream.Collectors;
    public class Demo2 {
        public static void main(String[] args) {
            //2.stream()代替流
            List<String> list = Arrays.asList("java", "python", "C++","php","java");
            List<String> listResult = list.stream().collect(Collectors.toList());
            //forEach遍历输出
            listResult.forEach(System.out::println);
        }
    }
    两个类都是如下结果输出：
    java
    python
    C++
    php
    java

二、将数据收集进一个集合(Stream 转换为 Set，不允许重复值，没有顺序)

package com.demo.stream.collectors;
    import java.util.Set;
    import java.util.stream.Collectors;
    import java.util.stream.Stream;
    public class StreamSet {
        public static void main(String[] args) {
            //1.将数据收集进一个集合(Stream 转换为 Set，不允许重复值，没有顺序)
            Stream<String> language = Stream.of("java", "python", "C++","php","java");
            Set<String> setResult = language.collect(Collectors.toSet());
            setResult.forEach(System.out::println);
        }
    }
    输出结果：
    python
    C++
    java
    php

三、用自定义的实现Collection的数据结构收集

package com.demo.stream.collectors;
    import java.util.Arrays;
    import java.util.LinkedList;
    import java.util.List;
    import java.util.TreeSet;
    import java.util.concurrent.CopyOnWriteArrayList;
    import java.util.stream.Collectors;
    public class StreamCollect {
        public static void main(String[] args) {
            List<String> list = Arrays.asList("java", "python", "C++","php","java");
            //用LinkedList收集
            List<String> linkedListResult = list.stream().collect(Collectors.toCollection(LinkedList::new));
            linkedListResult.forEach(System.out::println);
            System.out.println("--------------");
    
            //用CopyOnWriteArrayList收集
            List<String> copyOnWriteArrayListResult = list.stream().collect(Collectors.toCollection(CopyOnWriteArrayList::new));
            copyOnWriteArrayListResult.forEach(System.out::println);
            System.out.println("--------------");
    
            //用TreeSet收集
            TreeSet<String> treeSetResult = list.stream().collect(Collectors.toCollection(TreeSet::new));
            treeSetResult.forEach(System.out::println);
        }
    }
    输出结果：
    java
    python
    C++
    php
    java
    --------------
    java
    python
    C++
    php
    java
    --------------
    C++
    java
    php
    python

四、对Stream的字符串拼接

package com.demo.stream.collectors;
    import java.util.Arrays;
    import java.util.List;
    import java.util.stream.Collectors;
    public class StreamPinJie {
        public static void main(String[] args) {
            List<String> list = Arrays.asList("java", "python", "C++","php","java");
            //直接将输出结果拼接
            System.out.println(list.stream().collect(Collectors.joining()));
            //每个输出结果之间加拼接符号“|”
            System.out.println(list.stream().collect(Collectors.joining(" | ")));
            //输出结果开始头为Start--，结尾为--End，中间用拼接符号“||”
            System.out.println(list.stream().collect(Collectors.joining(" || ", "Start--", "--End")));
        }
    }
    输出结果：
    javapythonC++phpjava
    java | python | C++ | php | java
    Start--java || python || C++ || php || java--End

总结：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMwNzY0OTkx_size_16_color_FFFFFF_t_70][]

参考文档：[https://blog.csdn.net/qq\_39629277/article/details/83108585][https_blog.csdn.net_qq_39629277_article_details_83108585]

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[https_blog.csdn.net_qq_39629277_article_details_83108585]: https://blog.csdn.net/qq_39629277/article/details/83108585