When a person starts to learn Java or other programming languages, he will come into contact with the heap and the stack. Since there is no clear and clear explanation at the beginning, many people will have a lot of questions. What is the heap, what is the stack, and what is the heap and stack? the difference? What's worse is that there is a stack in Java, a last-in-first-out (Last In First Out) sequential data structure, which is java.util.Stack. In this case, it will inevitably make many people more confused about the previous question. In fact, the heap and stack are both parts of memory and have different functions, and a program needs to allocate memory in this area. As we all know, all Java programs run inside the JVM virtual machine. What we are introducing here is naturally the heap and stack in the JVM (virtual) memory.
the difference
The difference between heap and stack in Java is naturally a common question in interviews. The following points are the specific differences.
Everyone performs their duties
The main difference is that stack memory is used to store local variables and method calls.
The heap memory is used to store objects in Java. Whether it is member variables, local variables, or class variables, the objects they point to are stored in heap memory.
Exclusive or shared
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.
Objects in heap memory are visible to all threads. Objects in heap memory can be accessed by all threads.
Exception error
If there is no space available in the stack memory to store method calls and local variables, the JVM will throw java.lang.StackOverFlowError.
And if there is no available space in the heap memory to store the generated object, the JVM will throw java.lang.OutOfMemoryError.
Space size
The stack memory is much smaller than the heap memory. If you use recursion, your stack will fill up quickly. If the recursion does not break out in time, a StackOverFlowError problem is likely to occur.
You can set the stack memory size with the -Xss option. The -Xms option sets the starting size of the heap, and the -Xmx option sets the maximum heap size.
This is the difference between heap and stack in Java. If you understand this problem well, it can help you solve development problems, analyze heap memory and stack memory usage, and even perform performance tuning.
View default value(Updated)
To view the default value of the heap, use the following code, where InitialHeapSize is the size of the initial heap and MaxHeapSize is the maximum value of the heap.
Copy the code code as follows:
13:17 $ java -XX:+PrintFlagsFinal -version | grep HeapSize
uintx ErgoHeapSizeLimit = 0 {product}
uintx HeapSizePerGCThread = 87241520 {product}
uintx InitialHeapSize := 134217728 {product}
uintx LargePageHeapSizeThreshold = 134217728 {product}
uintx MaxHeapSize := 2147483648 {product}
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)
Check the default value of the stack, where ThreadStackSize is the size of the stack memory.
Copy the code code as follows:
13:21 $ java -XX:+PrintFlagsFinal -version | grep ThreadStackSize
intx CompilerThreadStackSize = 0 {pd product}
intx ThreadStackSize = 1024 {pd product}
intx VMThreadStackSize = 1024 {pd product}
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)
Translation information
Original English text: http://javarevisited.blogspot.com.au/2013/01/difference-between-stack-and-heap-java.html.
The translation has been modified, organized and deleted based on the original text. If you are interested, you can visit the original text. PS address has been blocked.