Java8新特性之Collectors.joining()实例详解

目录

• 方法定义
• 无参方法
• 单个参数
• 多个参数
• 如果流中的数据是字符串
• 如果流中的数据是对象
• 总结

方法定义

Java 8 流 ( stream ) 收集器 ( Collectors ) 中的 joining() 方法会返回一个 Collectors 实例，方便在流收集器上的链式操作。

Collectors.joining() 方法以遭遇元素的顺序拼接元素。我们可以传递可选的拼接字符串、前缀和后缀。

假设我们的流中有四个元素 ["A","B","C","D"]，那么我们就可以按照以下方式来收集它们。

无参方法

joinning() 无参数方法会返回一个 Collectors 实例，并且以空字符串 ( "" ) 来拼接收集到的所有元素

package com.sjh.test.java8;
 
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class JoiningTest1 {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("1","2","3","4");
        String result= list.stream().collect(Collectors.joining());
        System.out.println(result);
    }
}

运行结果：

/Library/Java/JavaVirtualMAChines/jdk1.8.0_171.jdk/...com.sjh.test.java8.JoiningTest1

1234

 

Process finished with exit code 0

单个参数

joining(CharSequence delimiter) 接受一个参数字符串序列作为拼接符，并返回一个 Collectors 实例。假如我们传递的拼接符为 "-" 。那么输出结果为 1-2-3-4

package com.sjh.test.java8;
 
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class JoiningTest2 {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("1","2","3","4");
        String result= list.stream().collect(Collectors.joining("-"));
        System.out.println(result);
    }
}

运行结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/...com.sjh.test.java8.JoiningTest2

1-2-3-4

 

Process finished with exit code 0

多个参数

joining(CharSequence delimiter, CharSequence prefix, CharSpythonequence suffix) 方法接受一个字符串序列作为拼接符，并在拼接完成后添加传递的前缀和后缀。假如我们传递的分隔符为 "-"，前缀为 "[" ， 后缀为 "]" 。那么输出结果为 [1-2-3-4]

package com.sjh.test.java8;
 
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class JoiningTest3 {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("1","2","3","4");
        String result= list.stream().collect(Collectors.joining("-", "[", "]"));
        System.out.println(result);
    }
}

运行结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/...com.sjh.开发者_JAVA教程test.java8.JoiningTest3

[1-2-3-4]

 

Process finished with exit code 0

如果流中的数据是字符串

使用 joinning() 的三种重载方法来拼接字符串

package com.sjh.test.java8;
 
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
 
public class JoniningDemo1 {
 
    public static void main(String[] args) {
        List<String> lisiFcCPCMCt = Arrays.asList("JayLa","LayMan","KangKang","XinYI");
        String resultStr = list.stream().collect(Collectors.joining());
        System.out.println(resultStr);
        resultStr= list.stream().collect(Collectors.joining(","));
        System.out.println(resultStr);
        resultStr= list.stream().collect(Collectors.joining("-","[","]"));
        System.out.println(resultStr);
    }
}

运行结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/...com.sjh.test.java8.JoniningDemo1

JayLaLayManKangKangXinYI

JayLa,LayMan,KangKang,XinYI

[JayLa-LayMan-KangKang-XinYI]

 

Process finished with exit code 0

如果流中的数据是对象

首先，我们创建一个 Person 类

package com.sjh.test.javjsa8.bean;
 
import java.util.ArrayList;
imporhttp://www.devze.comt java.util.List;
 
public class Person {
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name =iFcCPCMC name;
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public int getAge() {
        return age;
    }
    public static List<Person> getList() {
        List<Person> list = new ArrayList<>();
        list.add(new Person("JayLa", 23));
        list.add(new Person("LayMan", 20));
        list.add(new Person("KangKang", 25));
        list.add(new Person("XinYi", 18));
        return list;
    }
}

然后创建一个 Person 对象流

package com.sjh.test.java8;
 
import com.sjh.test.java8.bean.Person;
 
import java.util.List;
import java.util.stream.Collectors;
 
public class JoiningDemo2 {
    public static void main(String[] args) {
        List<Person> list = Person.getList();
 
        System.out.println("--Join person name--");
        String result= list.stream().map(p -> p.getName()).collect(Collectors.joining());
        System.out.println(result);
        result= list.stream().map(p -> p.getName()).collect(Collectors.joining("|"));
        System.out.println(result);
        result= list.stream().map(p -> p.getName()).collect(Collectors.joining("-","[","]"));
        System.out.println(result);
 
        System.out.println("--Join person age--");
        result= list.stream().map(p -> String.valueOf(p.getAge())).collect(Collectors.joining());
        System.out.println(result);
        result= list.stream().map(p -> String.valueOf(p.getAge())).collect(Collectors.joining("|"));
        System.out.println(result);
        result= list.stream().map(p -> String.valueOf(p.getAge())).collect(Collectors.joining("-","[","]"));
        System.out.println(result);
 
        System.out.println("--Join person name-age--");
        result= list.stream().map(p -> p.getName()+"-" + p.getAge()).collect(Collectors.joining("|"));
        System.out.println(result);
        result= list.stream().map(p -> p.getName()+"-" + p.getAge()).collect(Collectors.joining("|","[","]"));
        System.out.println(result);
    }
}

运行结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/...com.sjh.test.java8.JoiningDemo2

 

--Join person name--

JayLaLayManKangKangXinYi

JayLa|LayMan|KangKang|XinYi

[JayLa-LayMan-KangKang-XinYi]

 

 --Join person age--

23202518

23|20|25|18

[23-20-25-18]

 

 --Join person name-age--

JayLa-23|LayMan-20|KangKang-25|XinYi-18

[JayLa-23|LayMan-20|KangKang-25|XinYi-18]

 

Process finished with exit code 0

总结

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