Use java's StringBuilder.ensureCapacity() function to set the minimum capacity of the string buffer

Use java's StringBuilder.ensureCapacity() function to set the minimum capacity of the string buffer

StringBuilder is one of the common string operation classes provided in Java. It can be based on the current string buffer. Add, delete, modify and other operations on strings are performed on it, which is more efficient and flexible than the String class. However, the performance of StringBuilder will also be affected to a certain extent when performing a large number of string concatenation operations. In order to optimize the performance of StringBuilder, we can use the ensureCapacity() function to set the minimum capacity of the string buffer to reduce the number of expansions and improve operating efficiency.

ensureCapacity(int minimumCapacity) is a method in the StringBuilder class, used to ensure that the capacity of StringBuilder reaches at least the specified value minimumCapacity. If the current capacity of StringBuilder is less than minimumCapacity, it will be automatically expanded to the size of minimumCapacity. In this way, when performing a large number of string operations, we do not need to expand the capacity frequently, thus saving time and resources.

The following is a sample code that demonstrates how to use the ensureCapacity() function to set the minimum capacity of the StringBuilder string buffer:

public class StringBuilderExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();

        // 添加10000次字符串操作，测试扩容次数
        long startTime = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            sb.append("hello");
        }
        long endTime = System.currentTimeMillis();
        System.out.println("未设置最小容量，耗时：" + (endTime - startTime) + "ms");

        sb = new StringBuilder();
        sb.ensureCapacity(50000); // 设置最小容量为50000

        startTime = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            sb.append("hello");
        }
        endTime = System.currentTimeMillis();
        System.out.println("设置最小容量为50000，耗时：" + (endTime - startTime) + "ms");
    }
}

Running the above code, we can get the following output:

未设置最小容量，耗时：8ms
设置最小容量为50000，耗时：5ms

It can be seen that when performing a large number of string operations, the StringBuilder with the minimum capacity set to 50000 takes less time than the StringBuilder without the minimum capacity set. This is because after setting the minimum capacity, StringBuilder does not need to perform frequent expansion operations, thus improving operating efficiency.

It should be noted that in actual applications, we should set the minimum capacity reasonably according to the specific situation. If we know exactly the number of string operations, we can set the minimum capacity to a reasonable value slightly larger than the number of operations based on experience. However, if the number of operations cannot be determined, we can set the minimum capacity through some rules or experience to ensure that the performance of StringBuilder can be improved when a large number of string operations are performed.

Summary:
This article introduces how to use java's StringBuilder.ensureCapacity() function to set the minimum capacity of the string buffer to improve the performance of StringBuilder. By setting the minimum capacity appropriately, we can reduce the number of expansions and improve the efficiency of string operations. In practical applications, we should set the minimum capacity reasonably according to the specific situation to ensure that the advantages of StringBuilder can be used when operating a large number of strings.

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