1. An overview of the
1.1 Java Virtual Machine family
1.1.1 HotSpot VM
Oracle JDK and OpenJDK built-in virtual machine, the most mainstream and most widely used Java virtual machine.
1.1.2 J9 VM
1.1.3 Zing VM
1.2 Java VM Execution Process
When executing a Java program, its execution flow is as follows:
- Compile time environment
- Runtime environment
2. Java VM structure
2.1 Class file format
Class file format:
2.2 Class lifecycle
2.3 Class loading system
- Bootstrap ClassLoader
- Extensions ClassLoader
- Application ClassLoader/System ClassLoader
2.4 Runtime data area
These data areas are the program counter, Java virtual machine stack, local method stack, Java heap, and method area.
2.4.1 Program counter
2.4.2 Java Vm Stack
2.4.3 Local method stack
2.4.4 Java heap
2.4.5 method area
2.4.6 Runtime constant pool
3. Object creation
When the virtual machine receives a new command, it does the following:
4. Heap memory layout of objects
5. Oop – klass model
6. Spam algorithm
6.1 References in Java
- Strong reference
- Soft references
- A weak reference
- Phantom reference
6.2 Reference counting method
Disadvantages: Reference counting algorithms do not solve the problem of objects referring to each other circularly.
6.3 Root Search Algorithm
Advantages: Resolved that dead objects cannot be reclaimed because they reference each other.
