In-depth analysis of the initialization of member variables and local variables

1. Member variables
Member variables can be initialized without explicit initialization, because the virtual machine assigns a default value to it.
Because the member variables are part of the instance object, and all the instance objects are allocated in the heap memory, when the storage space is allocated in the virtual machine, the member variables of the memory space of the instance object are all allocated.Default initialization, so member variables have value even if you don't explicitly initialize them (the default value for primitive data types is 0, and the default value for reference data types is Null).

2. Local variables
Local variables must be initialized, otherwise they cannot be used.
First of all, local variables are located in the method, and each method is placed in the stack of the runtime data area during the execution of the JVM, and each stack stores the local variable table, operand stack, method exit, dynamic links, etc.Because the memory space required by the local variable table is fixedly allocated during compilation, before the method is called (that is, before the method is pushed onto the stack), it is necessary to determine how much variable space the method stack needs to allocate.It will not change the size of the local variable table, so it means that local variables must be initialized when they are created to determine the size of the allocated memory.