Java中的字符串串联

清疚 2023-02-28 06:14 19阅读 0赞

String Concatenation in java is very common. Being a Java developer, you are aware that every once in a while we write code for **String concatenation**.

Java中的字符串连接非常常见。 作为Java开发人员，您会意识到我们偶尔会为**String串联**编写代码。

## Java中的字符串串联 **(****String Concatenation in Java****)** ##

[![String concatenation in java, java string concat, java string append][String concatenation in java_ java string concat_ java string append]][String concatenation in java_ java string concat_ java string append_String concatenation in java_ java string concat_ java string append]

I am sure that you might have heard that we should not use String “+” operator for string concatenation in java. Also we should use [StringBuffer][] or [StringBuilder][] for this purpose. It’s a very common [java interview questions][] and you should be prepared for it.

我确信您可能已经听说过，我们不应该在Java中使用字符串“ +”运算符进行字符串连接。 同样，我们应该为此使用[StringBuffer][]或[StringBuilder][] 。 这是一个非常常见的[Java面试问题][java interview questions] ，您应该为此做好准备。

If you have dug deeper, you might know that String internally uses StringBuffer (till Java 1.4) or [StringBuilder][] (Java 1.5 onwards) for String “+” operator calls.

如果您更深入地研究，您可能会知道String内部使用StringBuffer（直到Java 1.4）或[StringBuilder][] （从Java 1.5开始）进行String“ +”运算符调用。

Let’s write a very simple String concatenation java program to prove this.

让我们编写一个非常简单的String串联java程序来证明这一点。

package com.journaldev.string.concatenation;
    
    public class StringConcatenationExample {
    
    	public static void main(String args[]){
    		String str = new String ("Journal  ");
    		str += "Dev!!";
    	}
    
    }

Now we will edit the same program to use StringBuffer.

现在，我们将编辑同一程序以使用StringBuffer。

package com.journaldev.string.concatenation;
    
    public class StringConcatenationExample {
    
    	public static void main(String args[]){
    	     StringBuffer str = new StringBuffer ("Journalbytecode");
    	     str.append("Dev!!");
    	}
    
    }

I have kept aside the byte code for both these programs, as you can see the only difference between both these programs are in line no 6 and 7. Let’s check out the byte code now.

我将这两个程序的字节码放在一边，因为您可以看到这两个程序之间的唯一区别是第6行和第7行。现在让我们检查一下字节码。

**String Concatenation Byte Code**

**字符串串联字节码**

˛∫æ2.com/journaldev/string/concatenation/StringConcatenationExamplejava/lang/Object<init>()VCode
    	LineNumberTableLocalVariableTablethisLcom/journaldev/string/concatenation/StringConcatenationExample;main([Ljava/lang/String;)Vjava/lang/String	Journal
    (Ljava/lang/String;)Vjava/lang/StringBuilder
    valueOf&(Ljava/lang/Object;)Ljava/lang/String;
    Dev!!
    !"#append-(Ljava/lang/String;)Ljava/lang/StringBuilder;
    %&'toString()Ljava/lang/String;args[Ljava/lang/String;strLjava/lang/String;
    SourceFileTTT.java!/*∑±
    
    	[ªY∑LªY+∏∑∂ ∂$L±
    
    ()
    *+,-

**StringBuffer append byte code**

**StringBuffer追加字节码**

˛∫æ2#com/journaldev/string/concatenation/StringConcatenationExamplejava/lang/Object<init>()VCode
    	LineNumberTableLocalVariableTablethisLcom/journaldev/string/concatenation/StringConcatenationExample;main([Ljava/lang/String;)Vjava/lang/StringBufferJournal
    (Ljava/lang/String;)VDev!!
    append,(Ljava/lang/String;)Ljava/lang/StringBuffer;args[Ljava/lang/String;strLjava/lang/StringBuffer;
    SourceFileTTT.java!/*∑±
    
    	NªY∑L+∂W±
    
    
     !"

From the byte code, it’s very clear that internally String + is using StringBuilder append method for string concatenation in Java.

从字节码中可以很清楚地看出，内部String +在Java中使用StringBuilder append方法进行字符串连接。

### Java中使用+运算符的字符串连接说明 **(****String Concatenation in java using + operator explained****)** ###

Here are the steps involved in String concatenation using + operator:

以下是使用+运算符进行字符串连接的步骤：

1.  A new StringBuilder object is created
    
    创建一个新的StringBuilder对象
2.  String “Journal” is copied to the newly created StringBuilder object
    
    将字符串“ Journal”复制到新创建的StringBuilder对象
3.  StringBuilder append() method is called to append “Dev !!” to the object
    
    调用StringBuilder append（）方法来追加“ Dev !!” 到对象
4.  StringBuilder toString() method is called to get the String object
    
    调用StringBuilder toString（）方法获取String对象
5.  The new String object reference is assigned to str and older string “Journal” is now available for garbage collection.
    
    新的String对象引用已分配给str，而旧的字符串“ Journal”现在可用于垃圾回收。

### 使用附加的字符串连接说明 **(****String concatenation using append explained****)** ###

If we are using StringBuffer or StringBuilder object, it’s done in following steps:

如果我们使用StringBuffer或StringBuilder对象，请按照以下步骤操作：

1.  A new StringBuffer object is created with value “Journal “
    
    创建一个新的StringBuffer对象，其值为“ Journal”
2.  append() method is called to to append “Dev !!” to the object
    
    调用append（）方法以追加“ Dev !!” 到对象
3.  StringBuffer toString() method is called to get the String object
    
    调用StringBuffer toString（）方法以获取String对象

Clearly second way is less time consuming and use less resources and produces less garbage collection.

显然，第二种方式可以节省时间，减少资源消耗并减少垃圾收集。

If you are interested in learning more about these, read [String vs StringBuffer vs StringBuilder][].

如果您想了解更多有关这些的知识，请阅读[String vs StringBuffer vs StringBuilder][] 。

Read this post to see how much [StringBuilder is faster than StringBuffer][] in java.

阅读这篇文章，看看在Java中[StringBuilder比StringBuffer快][StringBuilder is faster than StringBuffer]多少。

[GitHub Repository][]. [GitHub存储库中][GitHub Repository]检出更多String程序。

Reference: [String API Doc][]

参考： [字符串API文档][String API Doc]

> 翻译自: [https://www.journaldev.com/542/string-concatenation-in-java][https_www.journaldev.com_542_string-concatenation-in-java]

[String concatenation in java_ java string concat_ java string append]: http://imgconvert.csdnimg.cn/aHR0cHM6Ly9jZG4uam91cm5hbGRldi5jb20vd3AtY29udGVudC91cGxvYWRzLzIwMTIvMTAvc3RyaW5nLWNvbmNhdGVuYXRpb24taW4tamF2YS5wbmc?x-oss-process=image/format,png
[String concatenation in java_ java string concat_ java string append_String concatenation in java_ java string concat_ java string append]: https://cdn.journaldev.com/wp-content/uploads/2012/10/string-concatenation-in-java.png
[StringBuffer]: https://www.journaldev.com/16827/stringbuffer-in-java
[StringBuilder]: https://www.journaldev.com/16833/java-stringbuilder
[java interview questions]: https://www.journaldev.com/java-interview-questions
[String vs StringBuffer vs StringBuilder]: https://www.journaldev.com/538/string-vs-stringbuffer-vs-stringbuilder
[StringBuilder is faster than StringBuffer]: https://www.journaldev.com/137/stringbuffer-vs-stringbuilder
[GitHub Repository]: https://github.com/journaldev/journaldev/tree/master/CoreJavaProjects/String-Programs
[String API Doc]: https://docs.oracle.com/javase/7/docs/api/java/lang/String.html
[https_www.journaldev.com_542_string-concatenation-in-java]: https://www.journaldev.com/542/string-concatenation-in-java