String constant
Stringbuffer string variable (thread safety)
Stringbuilder string variable (non-thread-safe)
In short, the main performance difference between the string type and the stringbuffer type is that the string type is an immutable object, therefore, every time the string type is changed, it is equivalent to generating a new String object, and then pointing the pointer to the New String object, therefore, it is best not to use a string that often changes the content, because every time an object is generated, it will affect the system performance, especially when there are more referenced objects in the memory, the GC of JVM will start to work, and the speed will be quite slow.
If the stringbuffer class is used, the results will be different. Each result will operate on the stringbuffer object itself, instead of generating a new object, and then change the object reference. Therefore, we generally recommend using stringbuffer, especially when string objects change frequently. In some special cases, the String concatenation of the string object is actually interpreted by JVM as the concatenation of the stringbuffer object. Therefore, the speed of the string object in these cases is not slower than that of the stringbuffer object, in particular, in the generation of the following string objects, the string efficiency is far higher than that of stringbuffer.
Kuaidi:
String S1 = "this is only a" + "simple" + "test ";
Stringbuffer sb = new stringbuilder ("This is only a"). append ("simple"). append ("test ");
You will be surprised to find that the speed of generating the string S1 object is too fast, and the stringbuffer speed is not dominant at all. In fact, this is a JVM trick.
String S1 = "this is only a" + "simple" + "test"; actually:
String S1 = "this is only a simple test"; so of course it doesn't take much time. However, you should note that if your string is from another string object, the speed will not be so fast. For example:
String S2 = "this is only ";
String S3 = "simple ";
String S4 = "test ";
String S1 = S2 + S3 + S4;
At this time, JVM will follow the original method in a regular manner. In most cases, stringbuffer> string
Stringbuffer
Java. Lang. stringbuffer thread-safe variable character sequence. A string buffer similar to a string, but cannot be modified. Although it contains a specific character sequence at any time point, the length and content of the sequence can be changed by calling some methods.
The string buffer can be safely used for multiple threads. These methods can be synchronized as necessary, so all the operations on any specific instance are in serial order, this sequence is consistent with the method call sequence of each involved thread.
The main operations on stringbuffer are append and insert methods. You can reload these methods to accept any type of data. Each method can effectively convert the given data to a string, and then append or insert the character of the string into the string buffer. The append method always adds these characters to the end of the buffer, while the insert method adds the characters at the specified point.
For example, if z references a string buffer object whose current content is "start", this method calls Z. append ("Le") causes the string buffer to contain "startle", while Z. insert (4, "Le") will change the string buffer to include "starlet ".
In most cases, stringbuilder> stringbuffer
Java. Lang. stringbuilde
A variable character sequence of Java. Lang. stringbuilder is added to 5.0. This class provides a stringbuffer-compatible API, but does not guarantee synchronization. This class is designed as a simple replacement of stringbuffer, used when the string buffer is used by a single thread (this is common ). If possible, we recommend that you use this class first, because in most implementations, It is faster than stringbuffer. The two methods are basically the same.
Http://blog.csdn.net/rmn190/article/details/1492013
Personal Understanding (for reference only, please correct me ):
1. String is unchangeable, and stringbuffer/stringbuilder is variable.
2. the string class provides richer functions (compared with the other two ).
3. When you frequently perform string increase/decrease operations, consider using stringbuffer/stringbuilder in terms of performance optimization, because in this case, the essence of its work is to convert it into a variable sequence and then perform operations.
4. stringbuilder is a class that appeared at the beginning of jdk1.5. It has almost the same usage as stringbuffer, but it is non-thread-safe. Therefore, when a single thread does not need to consider thread security (synchronization issues), stringbuilder is preferred. because it does not have operations related to thread security, it has a slight performance advantage.
Recommended usage:
Stirng.
Stringbuffer: There are many operations to increase or decrease the number of strings. In multi-thread mode, synchronization needs to be considered (thread safety is required.
Stringbuilder: There are many operations to increase or decrease strings, so thread security is not required.
Http://snkcxy.iteye.com/blog/1807906
