Knowledge involved in JVM of Luban College
For Java programmers, JVM is a very important piece of many Java knowledge points, and this knowledge is often reviewed when java programmers are interviewed. Therefore, JVM must be mastered by java programmers. I specially sorted out some of the main knowledge points of JVM, hoping to help java programmers. The JVM system is generally divided into the following four parts:
1. Class loading mechanism. Focus on learning: ①. What is class loading; ②. Class life cycle; ③. Class loader; ④. Parent delegation model.
2. JVM memory structure.
①. The java heap (Heap) is the largest piece of memory managed by the java virtual machine. The java heap is a memory area shared by all threads and is created when the virtual machine starts. The sole purpose of this memory area is to store object instances, and almost all object instances allocate memory here;
②. Method area (Method Area), like the java heap, is a memory area shared by each thread, which is used to store class information, constants, static variables, and just-in-time compiler compilation that have been loaded by the virtual machine The following code and other data;
③. Program Counter Register, Program Counter Register is a small memory space, its function can be seen as the line number indicator of the bytecode executed by the current thread;
④. JVM stack (JVM Stacks), like the program counter, the java virtual machine stack (java Virtual Machine Stacks) is also thread private, and its life cycle is the same as that of the thread. The virtual machine stack describes the memory model of java method execution: when each method is executed, a stack frame is created at the same time to store information such as the local variable table, operation stack, dynamic link, and method exit. The process from when each method is called to the completion of execution corresponds to the process of a stack frame from pushing to popping in the virtual machine stack;
⑤. Native method stacks (Native Method Stacks), native method stacks (Native Method Stacks) and virtual machine stacks play very similar roles, the difference is that the virtual machine stack executes java methods for the virtual machine (that is, byte Code) service, and the native method stack serves the Native method used by the virtual machine.
3. GC algorithm, garbage collection. Key learning: ①. Judgment of object survival; ②. GC algorithm; ③. Garbage collector.
4. GC analysis, order tuning. Key learning: ①. GC log analysis; ②. Tuning commands; ③. Tuning tools.