Detailed introduction to String StringBuilder and StringBuffer in Java and usage examples

This article mainly introduces the detailed explanation and usage examples of String StringBuilder and StringBuffer in Java. Friends in need can refer to it

In Android/Java development, used to process strings There are three commonly used classes: String, StringBuilder, and StringBuffer.

Their similarities and differences:

1) They are all final classes, and they are not allowed to be inherited;
2) The length of String is immutable , the lengths of StringBuffer and StringBuilder are variable;
3) StringBuffer is thread-safe, but StringBuilder is not thread-safe.

String VS StringBuffer

The main performance difference between the String type and StringBuffer: String is an immutable object, so every time the String type is changed Every time, a new String object will be generated, and then the pointer will point to the new String object. Therefore, it is best not to use String for strings that frequently change content, because each time an object is generated, it will have an impact on system performance, especially when there are no references in the memory. When there are too many objects, the JVM's GC will start to work and performance will decrease.

When using the StringBuffer class, the StringBuffer object itself will be operated every time instead of generating a new object and changing the object reference. Therefore, it is recommended to use StringBuffer in most cases, especially when string objects change frequently.

In some special cases, the string concatenation of String objects is actually compiled into the concatenation of StringBuffer objects by Java Compiler, so in these cases the speed of String objects will not be slower than that of StringBuffer objects, for example:

String s1 = “This is only a” + “ simple” + “ test”;
StringBuffer Sb = new StringBuilder(“This is only a”).append(“ simple”).append(“ test”);

The speed of generating String s1 objects is not slower than StringBuffer. In fact, in Java Compiler, the following conversion is automatically done:

Java Compiler directly compiles the first statement above into:

String s2 = “This is only a”; 
String s3 = “ simple”; 
String s4 = “ test”; 
String s1 = s2 + s3 + s4;

This At this time, Java Compiler will do it in the original way. The concatenation (i.e. +) operation of String is implemented by the append method of StringBuilder (or StringBuffer). At this time, for the above situation, if s2, s3, s4 adopt String definition, when splicing, you need to create an additional StringBuffer (or StringBuilder), and then convert the StringBuffer to String; if you use StringBuffer (or StringBuilder), you do not need to create an additional StringBuffer.

StringBuilder

StringBuilder is new in 5.0. This class provides a StringBuffer-compatible API but does not guarantee synchronization. This class is designed as a drop-in replacement for StringBuffer when the string buffer is used by a single thread (which is a common situation). It is recommended to prefer this class if possible, as it is faster than StringBuffer in most implementations. The methods for both are basically the same.

Usage strategy

1) Basic principles: If you want to operate a small amount of data, use String; if you want to operate a large amount of data with a single thread, use StringBuilder; if you want to operate a large amount of data with a multi-thread, Use StringBuffer.

2) Do not use the "+" of the String class for frequent splicing, because the performance is extremely poor. You should use the StringBuffer or StringBuilder class. This is an important point in Java optimization. the rules. For example:

String result = ""; 
for (String s : hugeArray) { 
 result = result + s; 
} 

// 使用StringBuilder 
StringBuilder sb = new StringBuilder(); 
for (String s : hugeArray) { 
 sb.append(s); 
} 
String result = sb.toString();

When the above situation occurs, obviously we have to use the second method, because with the first method, every loop will Create a String result to save the result, except that the two are basically the same.

3) StringBuilder is generally used inside methods to complete functions similar to "+", because it is thread-unsafe, so it is used up It can be discarded later. StringBuffer is mainly used in global variables.

4) Under the same circumstances, using StirngBuilder can only achieve a performance improvement of about 10%~15% compared to using StringBuffer, but it will run the risk of multi-threading insecurity. In actual modular programming, the programmer responsible for a certain module may not necessarily be able to clearly judge whether the module will be run in a multi-threaded environment. Therefore: unless it is determined that the bottleneck of the system is on StringBuffer, and you are sure that StringBuilder can be used only if the module does not run in multi-threaded mode; otherwise, StringBuffer is still used.

The above is a detailed introduction to the detailed explanation and usage examples of String StringBuilder and StringBuffer in Java. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!