Java中String、StringBuffer和StringBuilder的區別——附示例

已發表: 2022-01-30
Java中String、StringBuffer和StringBuilder的區別-附比較和示例

在本 Java 教程中，我們將討論 Java String、StringBuffer 和 StringBuilder 之間的區別。

讓我們開始吧：

細繩：

String 類表示字符串。 Java 程序中的所有字符串文字，例如“crunchify”，都是作為此類的實例實現的。 字符串是常量； 它們的值在創建後無法更改。

字符串緩衝區：

一個線程安全的、可變的字符序列。 字符串緩衝區類似於字符串，但可以修改。

在任何時候它都包含一些特定的字符序列，但是序列的長度和內容可以通過某些方法調用來改變。

字符串緩衝區可以安全地被多個線程使用。

字符串生成器：

可變的字符序列。 此類提供與 StringBuffer 兼容的 API，但不保證同步。

此類設計用於在單個線程正在使用字符串緩衝區的地方（通常情況下）用作 StringBuffer 的替代品。

在可能的情況下，建議優先使用此類而不是 StringBuffer，因為它在大多數實現下會更快。

讓我們比較一下 String、StringBuffer 和 StringBuilder 的以下所有特性。

細繩字符串緩衝區字符串生成器
線程安全嗎？ 是的是的不
同步？ 是的是的不
可修改？ 否（不可變） 是（可變） 是（可變）
貯存字符串池堆堆
表現慢快速地快點

Java代碼：

  • 創建類：CrunchifyStringVsStringBufferVsStringBuilder.java
  • 將以下代碼放入其中
  • 保存存檔

在本教程中，我們添加、追加字符串總計 199999 次。

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package crunchify . com . tutorial ;
 
/**
* @author Crunchify.com
* Program: Difference between String, StringBuffer and StringBuilder in Java - Example attached
*/
 
public class CrunchifyStringVsStringBufferVsStringBuilder {
 
     public static void main ( String [ ] args ) {
 
         // String: The String class represents character strings. All string literals
         // in Java programs, such as "abc", are implemented as instances of this class.
         // Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings.
         // Because String objects are immutable they can be shared.
         String crunchifyString = "" ;
         long crunchifyBefore = System . currentTimeMillis ( ) ;
         for ( int i = 0 ; i < 199999 ; i ++ ) {
             crunchifyString = crunchifyString + "crunchify.com" ;
         }
 
         long crunchifyAfter = ( System . currentTimeMillis ( ) ) ;
         crunchifyPrint ( "Task Completion Time for String: " + ( crunchifyAfter - crunchifyBefore ) ) ;
 
         // StringBuffer: A thread-safe, mutable sequence of characters. A string buffer is like a String,
         // but can be modified. At any point in time it contains some particular sequence of characters, but the length
         // and content of the sequence can be changed through certain method calls.
         //
         // String buffers are safe for use by multiple threads. The methods are synchronized where necessary so that all
         // the operations on any particular instance behave as if they occur in some serial order that is consistent with the order
         // of the method calls made by each of the individual threads involved.
         //
         // The principal operations on a StringBuffer are the append and insert methods,
         // which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends
         // or inserts the characters of that string to the string buffer.
         // The append method always adds these characters at the end of the buffer;
         // the insert method adds the characters at a specified point.
 
         crunchifyBefore = System . currentTimeMillis ( ) ;
         StringBuffer crunchifyStringBuffer = new StringBuffer ( ) ;
         for ( int i = 0 ; i < 199999 ; i ++ ) {
             crunchifyStringBuffer . append ( "crunchify.com" ) ;
         }
 
         crunchifyAfter = ( System . currentTimeMillis ( ) ) ;
         crunchifyPrint ( "Task Completion Time for StringBuffer: " + ( crunchifyAfter - crunchifyBefore ) ) ;
 
         // StringBuilder: A mutable sequence of characters.
         // This class provides an API compatible with StringBuffer, but with no guarantee of synchronization.
         // This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread
         // (as is generally the case). Where possible,
         // it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.
         //
         // The principal operations on a StringBuilder are the append and insert methods,
         // which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends
         // or inserts the characters of that string to the string builder.
         // The append method always adds these characters at the end of the builder; the insert method adds the characters at a specified point.
 
         crunchifyBefore = System . currentTimeMillis ( ) ;
         StringBuilder crunchifyStringBuilder ;
         crunchifyStringBuilder = new StringBuilder ( ) ;
 
         for ( int i = 0 ; i < 199999 ; i ++ ) {
             crunchifyStringBuilder . append ( "crunchify.com" ) ;
         }
         // OR using repeat().
         // crunchifyStringBuilder.append("crunchify.com".repeat(199999));
         // repeat(): Returns a string whose value is the concatenation of this string repeated count times.
 
         crunchifyAfter = ( System . currentTimeMillis ( ) ) ;
         crunchifyPrint ( "Task Completion Time for StringBuilder: " + ( crunchifyAfter - crunchifyBefore ) ) ;
 
     }
 
     private static void crunchifyPrint ( String s ) {
         System . out . println ( s ) ;
     }
}
 

IntelliJ IDEA 控制台結果：

在 IntelliJ IDEA 或 Eclipse 控制台中將上述程序作為 Java 應用程序運行，您將得到如下結果。

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/ Users / app / app / Installation / jdk - 17.0.2.jdk / Contents / Home / bin / java - javaagent : / Applications / IntelliJ IDEA . app / Contents / lib / idea_rt . jar = 50109 : / Applications / IntelliJ IDEA . app / Contents / bin - Dfile . encoding = UTF - 8 - classpath : / Users / app / . m2 / repository / org / slf4j / log4j - over - slf4j / 1.7.32 / log4j - over - slf4j - 1.7.32.jar crunchify . com . tutorial . CrunchifyStringVsStringBuffer
 
Task Completion Time for String : 19648
Task Completion Time for StringBuffer : 7
Task Completion Time for StringBuilder : 3
 
Process finished with exit code 0
 

如果您在上面程序運行時遇到任何問題，或者在 String、StringBuffer 和 StringBuilder 之間有任何問題，請告訴我。