Java8新特性Stream之Collectors类型转换

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：

参考文档：https://blog.csdn.net/qq_39629277/article/details/83108585