Frames are allocated from the JVM stack of the thread creating the frame.A frame is destroyed when its method invocation completes. A new frame is created each time a method is invoked.A frame is used to store data and partial results, as well as to perform dynamic linking, return values for methods, and dispatch exceptions.Here’s are a few bullet point definitions of a Java Frame: Java Frames are a particularly important concept. The Sun documentation describes other memory concepts, such as these: If you’re digging into the Java heap and stack for some reason, it’s very important to know that there’s more to this story. It’s not specific to Java, but it provides a good definition: In a related note, I found this “stack vs heap” definition in a book named Algorithms. Another way to think about this is that if you end up having “memory leaks” in your code, the memory leaks will be in the heap, and a Java profiling tool can help you debug this problem. The memory for the heap does not need to be contiguous.Ī Java virtual machine implementation may provide the programmer or the user control over the initial size of the heap, as well as, if the heap can be dynamically expanded or contracted, control over the maximum and minimum heap size.Īgain, in lay terms, things like objects, class variables, and instance variables go on the heap. 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. Heap storage for objects is reclaimed by an automatic storage management system (known as a garbage collector) objects are never explicitly deallocated. The heap is created on virtual machine start-up. The heap is the runtime data area from which memory for all class instances and arrays is allocated. The Java virtual machine has a heap that is shared among all Java virtual machine threads. Here’s the definition of a Java heap, again with a few pieces removed for clarity: In layman’s terms, a simplification is to say that local variables and methods are on the Java stack. Because the Java virtual machine stack is never manipulated directly except to push and pop frames, frames may be heap allocated. A Java virtual machine stack stores frames.Ī 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. Here’s the definition of a Java stack, with a few pieces removed for clarity:Įach Java virtual machine thread has a private Java virtual machine stack, created at the same time as the thread. ![]() ![]() ![]() There’s no better source than the source, so directly from Sun’s Java website, here are definitions for the Java stack and Java heap. I just read a couple of emails about the concepts of a Java stack and heap, and thinking that their descriptions weren’t exactly right, I decided to do a little research. Summary: This article provides definitions and descriptions of the Java stack and heap.
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