You also don't want to put objects from the stack on the heap because it's less efficient if a method finishes all these local variables need to be found in this big collection. You don't want to put objects from the heap in the stack, because that means that they are lost whenever the method finishes. Now, why these two are not merged into one. The heap on the other hand is just a big collection of objects, each with a potentially different size. The stack is a somewhat linear piece of memory, and since each local variable has a fixed size** it is easy to maintain this memory. You call a method, its local variables are pushed on the stack, and once the finishes these methods get popped out of the stack again. This is just the way the stack is built, in just about any programming language. It's not a language that is assigned a stack/heap space, but a process. I think each time you start a new JVM, it will get it's own memory (although I'm less sure of this). In fact, it's possible that the OS manages all memory with a stack/heap method, so you can have stacks and heaps (for the JVM) inside of stacks and heaps (the OS). The OS would give java the memory from addresses 1000000 to 2000000 (which the JVM then divides into it's own stack/heap space) and C++ memory from 4500000 to 5500000, for example. A Java and C++ program might both have stack and a heap, but won't share one. many also use a stack/heap for their own internal memory management. Most modern programming languages give you a data structure called a stack - or you could write one. the reference will be in the program stack, but the object itself lives in the heap. The reason I wanted to back up is this.you can have a stack in your method. There are various algorithms for where exactly you pick it from, how you recover it, how you clean it up, etc. use the 'new' operator), you need memory that you can hang onto for a while. each time you need a chunk of memory (i.e. each time you return from a method, you 'pop' it off. Each time you call a new method, a new 'block' is pushed onto the stack, with the local variables. The stack is often used for function calls and storing local variables. They are generally though of as coming from opposite ends of a large contiguous block. Java then uses this memory in two ways - a stack, and a heap. when the jvm starts, your OS will say "Ok, the java process can have 2 gig of memory" or whatever. Most operating systems will give memory to processes (such as java) - i.e. There is a data structure called a stack, and a data structure called a heap. Let's back up for a second.'stack' and 'heap' are overloaded terms. We just know the data is stored somewhere. But we as programmers really don't need to care, most of the time. Sometimes the JVM may perform special tricks that violate this rule. Generally, local variables and parameters are stored on the stack, and instance and class variables (fields) are stored on the heap. In java program, how can i say a particular code is going to stack and a particular code is going to Heap? And there can easily be more than one stack or heap per language, as I discussed above. Each language may have a different way of organizing a stack or heap. I read, Heap is inside the JVM and it has three major parts or generations, so can i say each language or compiler will have different Heap altogether?Well, a compiler probably doesn't use a stack or heap at all. In fact, if you have a single Java program (one JVM) that using multiple threads, each thread has a separate stack - but they all share the same heap. In fact, even two Java programs (two separate JVMs) running on the same machine don't share the same stack or heap. Most programming languages use a stack and heap, but they don't share stack and heap. Is stack is common to all the program language? Say i have Java and C++ in my machine, so both share the same Stack? Pretty much any computer running a Java program has a stack and heap. Where is stack and Heap are located in the PC or in a server?īoth.
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