How to use the Java runtime constant pool?

The Java runtime constant pool is a part of the class file that stores literals and symbol references generated by the compiler. At runtime, the Java Virtual Machine loads these constants into memory and references them when needed.

The method of using the Java Runtime constant pool is as follows:

1. Direct literal usage: you can directly use literals from the constant pool, for example, string constants can directly use string objects from the constant pool.

String str1 = "Hello"; // 直接使用常量池中的字符串对象
String str2 = new String("Hello"); // 创建新的字符串对象

1. Symbolic references are used: In Java virtual machine, classes, methods, fields, etc. are stored as symbolic references in the constant pool, which can be accessed to access corresponding class, method, field information.

Class<?> clazz = Class.forName("java.lang.String"); // 使用符号引用获取类对象
Method method = clazz.getMethod("length"); // 使用符号引用获取方法对象
Field field = clazz.getField("CASE_INSENSITIVE_ORDER"); // 使用符号引用获取字段对象

1. Optimization of constant pool: The Java runtime constant pool has the function of constant pool caching, which can prevent the creation of duplicate literal objects.

String str1 = "Hello"; // 创建新的字符串对象
String str2 = "Hello"; // 直接使用常量池中的字符串对象
System.out.println(str1 == str2); // 输出true

It should be noted that the specific implementation of the Java runtime constant pool may vary depending on the Java virtual machine. The above usage method is applicable to most Java virtual machines. In some special cases, it may be necessary to optimize and adjust according to the specific Java virtual machine.