15.Java Basics - Heap & Stack
- 黄舟Original
- 2017-02-27 10:55:591253browse
Basic Concept
#In Java, there are six different places where data can be stored.
1. Register
is register. This is the fastest storage area because it is located inside the processor. The access speed is very fast and the program cannot control.
2. Stack
is stack, which is located in general-purpose RAM. It is second only to registers in storage speed. Needle.
It has the following characteristics:
Control memory through the stack pointer. If you move down, new memory is allocated; if you move up, that memory is released. So when creating a program, the Java compiler must know the exact size and lifetime of all data stored on the stack, because it must generate the appropriate code to move the stack pointer up and down
Stack memory belongs to a single thread. Each thread will have a stack memory, and the variables it stores can only be visible in the thread to which it belongs. That is, the stack memory can be understood as the private memory of the thread.
In-stack data sharing.
#Stores references to basic types of variable data, objects or arrays. But the object itself is not stored on the stack, but is stored on the heap (objects created by new) or in the constant pool (string constant objects are stored in the constant pool).
Have FILO first in last out rule.
3. Heap
is heap. Heap is a general memory pool (also exists in RAM). Used to store all Java objects. In layman's terms, it means to store all new objects.
The difference between the heap and the stack is that it has great flexibility in allocating storage, but it also takes longer. Because:
The compiler does not need to know how much storage area to allocate from the heap.
The compiler also does not have to know how long the stored data lives in the heap.
When you need to create an object, you only need to write a simple line of code; when this line of code is executed, storage will be automatically allocated in the heap.
4. Method area
is used to store loaded class information, constants, static variables, and code compiled by the just-in-time compiler.
5. Constant pool
The constant pool is part of the method area.
Store string constants and basic type variables, such as String str="www". In fact, "www" is in the constant pool.
Java’s 8 basic types (Byte, Short, Integer, Long, Character, Boolean, Float, Double). Except for Float and Double, the other six types all implement constant pools, but they only exist in (- 128 <= value<=127) uses the constant pool. Beyond this range, the constant pool will not be used and objects will be created directly in heap memory.
Basic Concept
In Java, there are six different places where data can be stored.
1. Register
is register. This is the fastest storage area because it is located inside the processor. The access speed is very fast and the program cannot control.
2. Stack
is stack, which is located in general-purpose RAM. It is second only to registers in storage speed. Needle.
It has the following characteristics:
Control memory through the stack pointer. If you move down, new memory is allocated; if you move up, that memory is released. So when creating a program, the Java compiler must know the exact size and lifetime of all data stored on the stack, because it must generate the appropriate code to move the stack pointer up and down
Stack memory belongs to a single thread. Each thread will have a stack memory, and the variables it stores can only be visible in the thread to which it belongs. That is, the stack memory can be understood as the private memory of the thread.
In-stack data sharing.
#Stores references to basic types of variable data, objects or arrays. But the object itself is not stored on the stack, but is stored on the heap (objects created by new) or in the constant pool (string constant objects are stored in the constant pool).
Have FILO first in last out rule.
3. Heap
is heap. Heap is a general memory pool (also exists in RAM). Used to store all Java objects. In layman's terms, it means to store all new objects.
The difference between the heap and the stack is that it has great flexibility in allocating storage, but it also takes longer. Because:
The compiler does not need to know how much storage area to allocate from the heap.
The compiler also does not have to know how long the stored data lives in the heap.
When you need to create an object, you only need to write a simple line of code; when this line of code is executed, storage will be automatically allocated in the heap.
4. Method area
is used to store loaded class information, constants, static variables, and code compiled by the just-in-time compiler.
5. Constant pool
The constant pool is part of the method area.
Store string constants and basic type variables, such as String str="www". In fact, "www" is in the constant pool.
Java’s 8 basic types (Byte, Short, Integer, Long, Character, Boolean, Float, Double). Except for Float and Double, the other six types all implement constant pools, but they only exist in (- 128 <= value<=127) uses the constant pool. Beyond this range, the constant pool will not be used and objects will be created directly in heap memory.
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