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This article mainly introduces "what is the difference between String, StringBuffer and StringBuilder in java". In daily operation, I believe many people have doubts about the difference between String, StringBuffer and StringBuilder in java. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the question of "what is the difference between String, StringBuffer and StringBuilder in java?" Next, please follow the editor to study!

String

The String class is immutable, that is, once a String object is created, the sequence of characters contained in the object is immutable until the object is destroyed.

This is the explanation of the String class. Xiao Xianer saw this situation before and could not understand the above explanation, as follows

String a = "123"; a =" 456 "; / / the printed an is 456System.out.println (a)

Seeing here, Xiao Xianer doesn't understand. Isn't it clear that he has been modified? Why is it said that he is an immutable class?

After the study of Xiao Xianer and his friends, I understand where the String class is immutable. Next, let's take a look at a memory storage space diagram of the above an object.

As you can see, when assigning a value again, instead of reassigning the instance object in the original heap, a generates a new instance object and points to the string "456", while a points to the newly generated instance object. the previous instance object still exists and will be garbage collected if it is not referenced again.

StringBuffer

The StringBuffer object represents a string with variable character sequence. When a StringBuffer is created, the character sequence of the string object can be changed through the methods provided by StringBuffer, such as append (), insert (), reverse (), setCharAt (), setLength (), and so on. Once the final desired string is generated through StringBuffer, you can call its toString () method to convert it to a String object.

StringBuffer b = new StringBuffer ("123"); b.append (" 456 "); / / b the printed result is: 123456System.out.println (b)

Take a look at the memory space diagram of the b object:

So the StringBuffer object is a string with a variable sequence of characters, it does not regenerate an object, and new strings can be concatenated in the original object.

StringBuilder

The StringBuilder class also represents a mutable string object. In fact, StringBuilder and StringBuffer are basically similar, and the constructors and methods of the two classes are basically the same. The difference is that StringBuffer is thread-safe, while StringBuilder does not implement thread-safety features, so the performance is slightly higher.

How does StringBuffer achieve thread safety?

The methods implemented in the StringBuffer class:

The methods implemented in the StringBuilder class:

Thus, the methods in the StringBuffer class all add the synchronized keyword, that is, a lock is added to the method to ensure thread safety.

Improvement of Java9

Java9 improves the implementation of strings (including String, StringBuffer, StringBuilder). Before Java9, the string used a char [] array to hold characters, so each character of the string was 2 bytes, while the string of Java9 used the byte [] array plus an encoding-flag field to hold characters, so each character of the string was only 1 byte. So Java9 strings save more space, and the functional methods of strings are not affected.

At this point, the study on "what is the difference between String, StringBuffer and StringBuilder in java" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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