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Java8新特性之Collectors.joining()實例詳解

更新時間：2023年01月12日 10:31:31 作者：Java小技巧

在項目中我們常常要對list集合的數(shù)據(jù)做一些字符串拼接/處理等相關(guān)操作,下面這篇文章主要給大家介紹了關(guān)于Java8新特性之Collectors.joining()的相關(guān)資料,需要的朋友可以參考下

方法定義

Java 8 流 ( stream ) 收集器 ( Collectors ) 中的 joining() 方法會返回一個 Collectors 實例，方便在流收集器上的鏈式操作。

Collectors.joining() 方法以遭遇元素的順序拼接元素。我們可以傳遞可選的拼接字符串、前綴和后綴。

假設(shè)我們的流中有四個元素 ["A","B","C","D"]，那么我們就可以按照以下方式來收集它們。

無參方法

joinning() 無參數(shù)方法會返回一個 Collectors 實例，并且以空字符串 ( "" ) 來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);
    }
}

運行結(jié)果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/...com.sjh.test.java8.JoiningTest1
1234

Process finished with exit code 0

單個參數(shù)

joining(CharSequence delimiter) 接受一個參數(shù)字符串序列作為拼接符，并返回一個 Collectors 實例。假如我們傳遞的拼接符為 "-" 。那么輸出結(jié)果為 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);
    }
}

運行結(jié)果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/...com.sjh.test.java8.JoiningTest2
1-2-3-4

Process finished with exit code 0

多個參數(shù)

joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix) 方法接受一個字符串序列作為拼接符，并在拼接完成后添加傳遞的前綴和后綴。假如我們傳遞的分隔符為 "-"，前綴為 "[" ，后綴為 "]" 。那么輸出結(jié)果為 [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);
    }
}

運行結(jié)果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_171.jdk/...com.sjh.test.java8.JoiningTest3
[1-2-3-4]

Process finished with exit code 0

如果流中的數(shù)據(jù)是字符串

使用 joinning() 的三種重載方法來拼接字符串

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> list = 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);
    }
}

運行結(jié)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

如果流中的數(shù)據(jù)是對象

首先，我們創(chuàng)建一個 Person 類

package com.sjh.test.java8.bean;
 
import java.util.ArrayList;
import java.util.List;
 
public class Person {
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name = 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;
    }
}

然后創(chuàng)建一個 Person 對象流

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);
    }
}

運行結(jié)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