Add a string to the string constant pool using java's String.intern() function

Use Java's String.intern() function to add a string to the string constant pool

In Java's string processing, you often encounter problems with string comparison and string splicing, especially This is when dealing with a large number of strings. In order to improve program performance and save memory space, Java provides a method to add strings to the string constant pool, that is, using the String.intern() function.

The string constant pool in Java is a special memory area used to store frequently used string objects for reuse. In Java, we usually use double quotes to directly create a string object, for example: "Hello". String objects created in this way are automatically added to the string constant pool. You can use the String.intern() function to manually add a string object to the string constant pool.

The following code example illustrates how to use the String.intern() function to add a string to the string constant pool.

public class StringInternExample {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = new String("Hello");
        String str3 = new String("Hello").intern();
        String str4 = new StringBuilder("Hel").append("lo").toString();
        String str5 = new StringBuilder("Ja").append("va").toString().intern();

        System.out.println("str1 == str2: " + (str1 == str2)); // false
        System.out.println("str1 == str3: " + (str1 == str3)); // true
        System.out.println("str1 == str4: " + (str1 == str4)); // false
        System.out.println("str1 == str5: " + (str1 == str5)); // true
    }
}

In the above example, we created 5 string objects. The string created by str1 using double quotes will be automatically added to the string constant pool, while the character created by str2 using the new keyword will be automatically added to the string constant pool. String creates a new object in the heap. We use the String.intern() function to manually add str3 to the string constant pool so that it references the same object as str1. str4 is a string spliced ​​by StringBuilder. A new object is created in the heap, which is different from the object referenced by str1. Finally, use the String.intern() function to add str5 to the string constant pool, referencing the same object as str1.

Running the program, we can find the following output results:

str1 == str2: false
str1 == str3: true
str1 == str4: false
str1 == str5: true

As can be seen from the output results, after using the String.intern() function to add the string to the string constant pool, through Comparing the reference values ​​of strings can determine whether two strings are equal. Because the string objects in the string constant pool are unique, reference judgment can avoid one-by-one comparison of character contents, thereby improving program performance.

It should be noted that after using the String.intern() function to add a string to the string constant pool, it will first search whether there is a string with the same content in the constant pool, and if so, it will return to the constant pool. Object in the constant pool, if not, create a new object in the constant pool. Therefore, you need to pay attention to memory usage when using the String.intern() function and avoid frequently adding a large number of string objects to the string constant pool.

In short, you can use Java's String.intern() function to add strings to the string constant pool to reuse string objects, thereby improving program performance and saving memory space. In actual development, the String.intern() function can be flexibly used according to specific scenarios to achieve the effect of optimizing the program.

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