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1. What is JVM (Java Virtual Machine)? What does it do?
2. What is the architecture of JVM? Can you explain the core components inside JVM?
3. How do Java programs run on JVM?
4. What is Java Bytecode? Why does it play an important role in Java?
5. How does JVM garbage collection work? What are the common garbage collection algorithms?
6. What is the class loading mechanism of JVM? Can you explain the class loading process?
7. What is a JIT (Just-In-Time) compiler? How does it relate to the JVM?
8. What aspects should be paid attention to when tuning the JVM performance?
9. What is the JVM's thread model? Can you explain the relationship between Java threads and operating system threads?
10. What are the common optimization techniques and tools for JVM?
11. What are JVM stack overflows and heap overflows? How to prevent them?
12. What is the memory model of JVM? Can you explain the concept and characteristics of Java Memory Model (JMM)?
13. What are the debugging tools for the JVM? How do you use them to debug Java programs?
14. What is the Java Security Manager? Can you explain its role and usage scenarios?
15. What is the JVM Native Interface (JNI)? How does it relate to the interaction between Java and other programming languages?
16. What tools and techniques are there for JVM performance monitoring?
17. What is inlining optimization? How is it implemented in the JVM?
18. Can a JVM use multiple class loaders? Why?
19. How does the JVM's bytecode execution engine work? Can you explain the difference between an interpreter and a just-in-time compiler?
20. How is JVM security guaranteed? What are the security mechanisms and strategies?

1. JVM (Java Virtual Machine) is one of the core components of the Java platform. It is responsible for translating Java programs into machine code and executing them. Its role is to provide an environment that allows Java programs to run on different operating systems and hardware, realizing the Java feature of "write once, run anywhere".

2. The JVM architecture is basically divided into three main parts: Class Loader, Runtime Data Area and Execution Engine. The Class Loader is responsible for loading class files into memory and generating corresponding class objects. The Runtime Data Area is divided into the method area, heap, program counter and virtual machine stack, which are used to store class metadata, object instances, thread program counters and method call stacks. The Execution Engine is responsible for interpreting and executing or compiling bytecodes.

3. The process of running a Java program on the JVM is roughly divided into three steps: compilation, loading, and execution. First, the Java source code is compiled into a bytecode file (.class file) by the Java compiler (javac). Then, the JVM's class loader loads the bytecode file into memory and generates the corresponding class object. Finally, the JVM's execution engine interprets and executes or compiles and executes the bytecode to run the Java program.

4. Java bytecode is an intermediate code, which is a binary file generated after Java source code is compiled. Java bytecode has the characteristics of being independent of a specific platform and can be interpreted or compiled on the JVM. One of the important functions of Java bytecode is to realize the "write once, run anywhere" feature of Java, so that Java programs can run on different platforms.

5. JVM's garbage collection is an important function of automatic memory management. It reclaims memory space by detecting and releasing objects that are no longer in use, thereby avoiding problems such as memory leaks and memory overflows. Common garbage collection algorithms include mark-sweep algorithm, copy algorithm, mark-compact algorithm, etc.

6. The class loading mechanism of JVM refers to the process of loading class files into memory and generating corresponding class objects. The class loading mechanism is mainly divided into three stages: loading, linking, and initialization. The loading stage is responsible for finding and loading class files, the linking stage is responsible for verifying, preparing, and parsing class files, and the initialization stage is responsible for initializing the static variables and static code blocks of the class.

7. The JIT (Just-In-Time) compiler is a compilation method of the JVM, which compiles bytecode into native machine code in real time to improve the execution speed of the program. The relationship between the JIT compiler and the JVM is that the JIT compiler is an important component of the JVM, which is responsible for compiling hot code (frequently executed code) into native machine code to optimize the execution efficiency of the program.

8. JVM performance tuning requires attention to multiple aspects, including memory management, garbage collection, thread concurrency, code optimization, etc. During the tuning process, you can improve program performance by adjusting the heap size, adjusting garbage collection parameters, using thread pools, etc.

9. The JVM thread model is implemented through the mapping relationship between Java threads and operating system threads. Java threads are composed of data structures such as the JVM virtual machine stack, native method stack, and program counter, and will eventually be mapped to operating system threads for execution. The mapping relationship between Java threads and operating system threads is a one-to-one or many-to-one relationship.

10. Common JVM optimization techniques and tools include code optimization, garbage collection tuning, concurrent programming, memory analysis tools, etc. Compiler optimization, JIT compiler, thread pool, etc. can be used to optimize the execution efficiency of the program.

11. JVM stack overflow and heap overflow are both cases of memory overflow. Stack overflow means that the JVM stack space is insufficient and new stack frames cannot be allocated, resulting in stack overflow. Heap overflow means that the JVM heap space is insufficient and new objects cannot be allocated, resulting in heap overflow. Stack overflow and heap overflow can be prevented by increasing the size of the stack or heap, optimizing recursive calls, etc.

12. The JVM's memory model refers to the memory access rules in Java programs. The Java Memory Model (JMM) specifies the rules for Java threads to access and modify shared memory, ensuring the visibility, orderliness, and atomicity of multi-threaded programs.

13. JVM debugging tools include jdb (Java debugger), jstack (thread stack information), jmap (memory mapping information), jstat (garbage collection statistics), etc. You can use these tools to locate and solve problems in Java programs.

14. The Java Security Manager is a security mechanism of the JVM that controls the secure access of Java programs by providing security policy files and permission management. The Java Security Manager can limit the program's access rights to files, networks, system resources, etc., thereby improving the security of the program.

15. The JVM's native interface (JNI) is a bridge between Java and other programming languages. It provides a set of standard interfaces that allow Java programs to call function libraries written in native languages. JNI enables interaction between Java and other programming languages ​​by defining Java native methods.

16. JVM performance monitoring tools and technologies include JMX (Java Management Extensions), VisualVM, Java Mission Control, etc. These tools can monitor the performance indicators, memory usage, garbage collection, etc. of the program in real time to help optimize the performance of the program.

17. Inline optimization refers to an optimization technique that directly replaces method calls with method bodies during compilation. The JVM decides whether to perform inline optimization by analyzing information such as the frequency and context of method calls. Inline optimization can improve program execution efficiency and reduce method call overhead.

18. JVM can use multiple class loaders to load class files, each class loader is responsible for loading a specific class file. Multiple class loaders are designed to provide a more flexible class loading mechanism and better support class loading and isolation in complex application scenarios.

19. The bytecode execution engine of JVM mainly uses interpreters and just-in-time compilers. The interpreter interprets and executes the bytecodes one by one, and the just-in-time compiler compiles the hot code into local machine code for execution. The execution speed of the interpreter is slower but has better portability, while the execution speed of the just-in-time compiler is faster but has a greater compilation overhead.

20. The security of JVM is ensured by mechanisms such as security manager, class loader, and access control. The security manager controls the Java program's access rights to system resources, the class loader implements class isolation and secure access, and the access control mechanism restricts the program's read and write operations on sensitive information, thereby improving the security of JVM.