Generational collection is a Java memory management technology that divides heap memory into different areas (generations) to optimize memory management of different object life cycles. The process includes: marking unreachable objects; clearing marked objects and releasing memory; moving surviving objects and optimizing memory layout.
Generational collection in Java memory management
In the Java Virtual Machine (JVM), generational collection is a A memory management technology that divides heap memory into different regions (called generations), each optimized for a different object life cycle.
The purpose of generational collection is to optimize memory management and reduce application pause time and garbage collection overhead. It does this by classifying objects by life cycle:
Young generation:
Old generation:
Persistent generation:
The process of generational collection:
Practical case:
The following Java code demonstrates how generational collection affects the life cycle of an object:
public class GenerationSample { public static void main(String[] args) { // 创建一个短期存活的对象 Object shortLivedObject = new Object(); // 创建一个长期存活的对象 Object longLivedObject = new Object(); // 保留对长期存活对象的引用,防止它被垃圾回收 longLivedObject = null; // 触发垃圾回收 System.gc(); // 检查短期存活对象是否已被清除 if (!isReachable(shortLivedObject)) { System.out.println("短期存活对象已清除"); } // 检查长期存活对象是否仍然存活 if (isReachable(longLivedObject)) { System.out.println("长期存活对象仍然存活"); } } private static boolean isReachable(Object object) { try { return new java.lang.ref.WeakReference<>(object).get() != null; } catch (Exception e) { return false; } } }
In this example , shortLivedObject
will be allocated to the young generation, and longLivedObject
will be allocated to the old generation. Since longLivedObject
is retained as a reference, it will survive until garbage collection. And shortLivedObject
will most likely be cleared since it is unreachable in the young generation.
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