What is the difference between String and StringBuffer in java? (difference comparison)

This article brings you what is the difference between String and StringBuffer in java? (Difference comparison), it has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Preface

1. String and StringBuffer are both classes for character operations in java

2. Especially String, we often see similar Such an assignment code, String str = "Hello World", looks like int and is thought to be the basic data type of Java. In fact, it is not. String is a class, a special class that can be assigned directly like the basic data type.

3. There are three classes in java that can operate on characters:

(1) Character is a class that performs single character operations.
(2) String is an immutable class that operates on a string of characters.
(3) StringBuffer also operates on a string of characters, but it is a variable class.

The difference between String and StringBuffer classes in Java

1. The content of the StringBuffer object can be modified; once the String object is generated, it cannot be modified and reassigned. In fact, there are two objects.

2. String is an object, not a primitive type; it is an immutable object, and once it is created, its value cannot be modified.

3. To modify an existing String object, you actually create a new object and then save the new value in it.

4. String is a final class and cannot be inherited.

5. StringBuffer is a mutable object. When it is modified, the object will not be re-established like String. It can only be established through the constructor. After the object is created, memory space will be allocated and a null will be initially saved. When assigning a value to StringBuffer, you can use its append method: obj.append("hello");

6. StringBuffer is more efficient than String in string connection operations.

7. If the program requires frequent modification and connection operations on strings, the performance of using StringBuffer will be higher.

8. In the String class, there is no method for changing a certain character in an existing string. Since you cannot change a single character in a java string, so in the JDK The documentation states that objects of the String class are immutable.

9. However, immutable strings have a big advantage: the compiler can make the string shared.

10. StringBuffer is thread-safe and can be easily used in multi-threaded programs, but the program execution efficiency is relatively slower.

11. The methods in the StringBuffer class focus on changes to strings, such as appending, inserting, and deleting. This is also the main difference between the StringBuffer and String classes.

String and StringBuffer connection string comparison

1. String str = new String("Hello World");str = "hello world"; The processing process of this string connection:

   (1) Create a StringBuffer;
   (2) Call the append() method;
   (3) Finally, the StringBuffer calls toString() to reassign the value of the String
   (4) It seems that the connection operation of String requires more operations than StringBuffer, and the efficiency will be compromised.
   (5) Moreover, since String is an immutable object, a new object will be created every time it is reassigned, so the original object will be useless and will be garbage collected, which will also affect performance.
   

2. #The StringBuffer class is an auxiliary class that can pre-allocate a memory block of a specified length to create a string buffer. In this way, using the append method of the StringBuffer class to append characters is much more efficient than using String's " " operator to add characters to the back of an existing string.

3. Use the " " operator. Every time you add characters to a string, the string object needs to find a new memory space to accommodate the larger string. This It is undoubtedly a very time-consuming operation. Adding multiple characters means reallocating memory for the string again and again. Using StringBuffer avoids this problem.

The above is the detailed content of What is the difference between String and StringBuffer in java? (difference comparison). For more information, please follow other related articles on the PHP Chinese website!