The relationship between direct memory and heap memory in Java

In Java programming, memory management is an important topic. The memory of a Java program can be divided into two main types: heap memory and direct memory. This article will introduce the concept, difference and relationship between Java direct memory and heap memory.

What is heap memory?

Heap memory is a memory area provided by Java virtual machine (JVM), which is mainly used to store object instances and arrays. The size of heap memory is dynamically allocated and is managed by the garbage collector. In heap memory, the creation, management and destruction of objects are done manually or automatically by Java programmers.

What is direct memory?

Direct memory is a piece of memory space allocated outside the heap, also known as non-heap memory. Direct memory usually passesByteBufferWhen operating classes, you can bypass the Java heap and directly interact with the operating system's memory. When using direct memory, memory allocation and release need to be managed with caution to avoid memory leaks and performance issues.

The relationship between heap memory and direct memory

Heap memory and direct memory are memory resources required for Java programs to run, but they are managed in different ways.
Heap memory is mainly used to store Java objects and is automatically managed by the JVM, while direct memory needs to be managed manually.
Direct memory is usually used in scenarios where frequent interactions with the operating system or require large memory space, such as network programming, file IO, etc.
By using ByteBuffer and other classes, you can operate direct memory in Java programs to achieve efficient memory read and write operations.

import ;
public class DirectMemoryExample {
    public static void main(String[] args) {
        // Allocate direct memory, size 1MB        ByteBuffer directBuffer = (1024 * 1024);
        // Simulate writing data in direct memory        (123);
        (3.14);
        // Read data in direct memory        ();
        ("Int value from direct memory: " + ());
        ("Double value from direct memory: " + ());
        // Release direct memory        ();
        directBuffer = null;
        // Assume there are other business logic codes here...        // When the direct memory is no longer used, manually release it        (); // Manually trigger garbage collection    }
}

In the above example code, we usedByteBufferTo operate direct memory. First, byallocateDirectThe method allocates 1MB of direct memory space and then usesputIntandputDoubleMethod writes data to direct memory. Then, byflipMethod flips the buffer, usegetIntandgetDoubleMethods read data in direct memory. Finally, when direct memory is no longer needed, we manually free up memory space,directBufferSet to null and trigger garbage collection manually to free up resources. This sample code simulates a simple direct memory operation scenario, showing how to allocate, write, read, and free direct memory. In practical applications, direct memory is usually used in scenarios such as high performance, large memory space or interaction with underlying systems. Developers need to be careful to manage direct memory to avoid memory leaks and performance problems.

Detailed explanation of Java memory management

In Java programming, memory management is an important topic. Java memory is mainly divided into heap memory (Heap) and stack memory (Stack), as well as method area (Method Area) and direct memory (Direct Memory). The following will introduce various aspects of Java memory management in detail:

1. Heap memory (Heap)

Heap memory is the largest memory area managed by a Java virtual machine (JVM) and is used to store object instances and arrays.
All objects created with the new keyword will be stored in heap memory, and the size of the heap memory is dynamically allocated.
The heap memory is managed by the garbage collector. When the object is no longer referenced, the garbage collector will automatically release the memory it occupies.

2. Stack memory (Stack)

The stack memory is used to store data such as local variables, method parameters, method return value and return address of method calls.
Each thread has its own stack memory, and the life cycle of the stack memory is the same as the thread life cycle.
The data in the stack memory follows the principle of "first in and then out". When the method is called, the data will be pushed to the top of the stack, and when the method returns, the data will be popped out of the top of the stack.

3. Method Area

The method area stores the structure information of the class, static variables, constants, method bytecode and other data.
The method area is a memory area shared by each thread, used for class information stored in memory.
In the newer JVM specification, the method area is replaced with a metaspace, which is no longer a part of the heap memory, but is stored directly in local memory.

4. Direct Memory

Direct memory is a piece of memory space allocated outside the heap, also known as non-heap memory.
Direct memory can be operated through the ByteBuffer class, usually used in scenarios where frequent interactions with the operating system or require large memory space.
Direct memory needs to be managed manually, and the developer is responsible for manually freeing the allocated memory space.

Summarize

Heap memory and direct memory are both important in Java, but their uses and management methods vary. Heap memory is used to store Java objects and is automatically managed by the JVM; while direct memory is used to directly interact with the operating system and needs to be managed manually. Correct understanding and using these two memory types can help improve the performance and efficiency of Java programs.

This is the end of this article about the relationship between Java direct memory and heap memory. For more related Java direct memory and heap memory content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!