Java中的堆内存和栈内存
本文主要讨论作者对于Java内存中堆栈的理解.
Oralce官方对于栈(stack)的解释：
Each Java Virtual Machine thread has a private Java Virtual Machine stack, created at the same time as the thread. A Java Virtual Machine stack stores frames (§2.6). A Java Virtual Machine stack is analogous to the stack of a conventional language such as C: it holds local variables and partial results, and plays a part in method invocation and return. Because the Java Virtual Machine stack is never manipulated directly except to push and pop frames, frames may be heap allocated. The memory for a Java Virtual Machine stack does not need to be contiguous.
- 栈中存放的是基本变量和对象的引用（或者叫引用变量）
- 栈在方法对象和返回结果的时候起作用
对于堆（heap）的解释:
Java Virtual Machine has a heap that is shared among all Java Virtual Machine threads. The heap is the run-time data area from which memory for all class instances and arrays is allocated.The heap is created on virtual machine start-up. Heap storage for objects is reclaimed by an automatic storage management system (known as a garbage collector); objects are never explicitly deallocated. The Java Virtual Machine assumes no particular type of automatic storage management system, and the storage management technique may be chosen according to the implementor's system requirements. The heap may be of a fixed size or may be expanded as required by the computation and may be contracted if a larger heap becomes unnecessary. The memory for the heap does not need to be contiguous.
- 堆中存放的是对象
- 当没有栈中的引用指向堆中的对象时，堆中的对象由自动垃圾回收器（garbage collector）负责回收,回收时间不确定
JVM是基于堆栈的虚拟机.JVM为每个新创建的线程都分配一个堆栈.也就是说,对于一个Java程序来说，它的运行就是通过对堆栈的操作来完成的。堆栈以帧为单位保存线程的状态。JVM对堆栈只进行两种操作:以帧为单位的压栈和出栈操作。
当前方法使用的帧称为当前帧。当线程激活一个Java方法,JVM就会在线程的 Java堆栈里新压入一个帧。这个帧自然成为了当前帧.在此方法执行期间,这个帧将用来保存参数,局部变量,中间计算过程和其他数据.