String, stringbuffer, stringbuilder comparison

1. See API;

• String is an unchangeable character sequence;
• Stringbuffer is a thread-safe, variable character sequence;
• Stringbuilder is a variable character sequence;

The difference between stringbuffer and string is that stringbuffer is variable (stringbuffer is regarded as variable string). The Character Sequence and length contained in stringbuffer can change with the method call; stringbuffer is secure in a multi-threaded environment, and all necessary methods are synchronized. Therefore, all methods on a specific instance are executed in sequence, the result is consistent with that of all methods in sequence.

The main operations of stringbuffer are insert and append, which can accept any type of data.

Stringbuffer: http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuffer.html

 

Stringbuilder provides APIs compatible with stringbuffer, but does not guarantee synchronization. Stringbuilder is designed to replace the stringbuffer class used in a single-threaded environment. If possible, stringbuilder is recommended, because stringbuilder is more efficient in most cases.

Stringbuilder is insecure in multi-threaded environments. stringbuffer is recommended in multi-threaded environments.

Stringbuilder: http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html

 

2. Reprinted;

Address: http://blog.csdn.net/rmn190/article/details/1492013

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 much faster than that of stringbuffer:

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. In the JVM's eyes, this string S1 = "this is only a" + "simple" + "test" is 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 a”;String S3 = “ simple”;String S4 = “ test”;String S1 = S2 +S3 + S4;

At this time, the 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

Stringbuilder

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.