How does Java object allocate memory?

Java object memory allocation uses the garbage collection mechanism to manage memory. The steps are as follows: The object header stores object status information. Instance data is stored in the object header. Memory alignment for efficiency.

Memory Allocation of Java Objects

The Java Virtual Machine (JVM) uses an automatic mechanism called garbage collection (GC) to Manage memory. The goal of GC is to avoid memory leaks by releasing memory occupied by objects that are no longer needed.

Object memory allocation

1. Object header

Every Java object has an object header, which stores the object Status information, for example:

• Hash code
• Identification hash
• GC information

2. Example Data

The object header stores the instance data of the object, including field and array references.

3. Alignment

In order to improve memory efficiency, the Java virtual machine allocates memory to objects according to specific alignment requirements. This depends on the type of object and the JVM implementation.

Practical case

The following code example shows allocating memory for an object in Java:

class Person {
    private String name;
    private int age;
}

Person person = new Person();

// 获取 person 对象的内存地址
long address = System.identityHashCode(person);

// 输出对象的内存地址
System.out.println("Object memory address: " + address);

This code creates a Person object and print its memory address. By getting the hash code of an object, we can determine the memory location of the object.

Other notes

• Allocating memory for primitive types: Primitive types (such as int, double) are stored directly on the stack.
• Static variables allocate memory: Static variables are stored in the static area, which is allocated memory when the class is loaded.
• Method call: Method call creates a new stack frame that allocates local variables and parameter space specific to the method.

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