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So let's go ahead and look at the contents of a stack frame.

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Here's an illustration of the stack frame of a method.

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It contains three things.

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A local with Eberts array and Upperton stack and also a reference to that runtime constant of the class

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of the current method.

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Look already was array as you may guess is an array that stores all the local variables and method since

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Midhat parameters are also local variables.

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They also get stored here.

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In fact method barometers are stored before local variables.

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And the idea if this method is an instance method then the element in the zero next will be a reference

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.

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That is a reference to the current object on the heap.

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And this is needed for accessing any instance do from within them either.

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But if the method is a static method then the zero element would be the first method parameter as a

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method to some sort before local variables that are declared in the body.

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I pop from local variables data that I read will also include the return address which is nothing but

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the memory address of the next instruction and the calling method.

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So if this method completes its execution successfully without any errors then the program counter is

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updated with this return address.

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Then GBM execution engine will exit give the instruction at that memory address.

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Now it's coming to open in-stock.

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It is similar to general purpose registers.

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In native you.

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It is a central focus of JVM instruction set as values are generally pushed onto it before they are

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used.

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Note is that we are using the word push here.

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And that's because our patent stack is a stack most byte code instructions involved moving values to

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and fro between the local variables array and the output in stack are put in stack is also used to receive

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any values that are written by methods invoked from the current method.

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Here's an example to illustrate how operant stack is used on the left we have a simple code fragment

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which initializes variables Y and Z and then assigns some to the variable x on the right.

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We have the corresponding bytecode instructions.

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Let's not have you want this bytecode instructions mean the first two instructions are generated due

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to the first statement and y equals to 1.

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The first instruction I Konst underscore one simply pushes the constant value one on the top of the

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open in-stock.

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So the suffix one indicates a constant value.

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One second instruction I store underscore one BOP's the value on the top of the operand stuck here.

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I and I start indicates the value to be part of any data type.

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The bottom line is it's stored in the local variables array at the end it's position 1.

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So suffixed one indicates the next position and the local variables are in.

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Next the third and fourth instructions are similar to forestall instructions and the corresponding The

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second statement in is equal to three.

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So the third instruction I cost underscore three pushes constant three on the opera in-stock.

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When the fourth instruction I start underscore to boost the value on the top of the operand stack and

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store it in the local variables array at index position 2.

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At this point the all put in stack is empty.

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When the local variables array has values 1 and 3 No the third statement is X equals Y policy in order

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to perform this operation.

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Venia to transfer the values from the local variables are you on to the operand stack.

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So the next two instructions I Laura underscore one.

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And I Lord underskirt boo boo.

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Exactly that I should underscore one takes the value add and mix position 1 in the local variables array

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and pushes it onto the top of the operand stock.

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Similarly I Lorena's go too big to evaluate inexpertly shouldn't do in the local variables array and

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pushes it onto the top of the operand stack.

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Next the instruction I add Boster and values on top of the operand stack and adds them on pushes the

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result back onto the upper end stack.

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Once again I and I add refers to integrate R-Type that is a boo or loose on the operand stack or off

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and did type since the sum is assigned to the variable x.

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We have the instruction eyes toward underskirt 3 which we know pops up and right now on the top of the

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operand stack which basically is the sum unstarted at the end ex-politician 3 in the local variables

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.

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So store instruction is basically moving the value from the open and stack to the local variables array

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.

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Well the load instruction is doing the exact opposite.

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So with that the local variables are the highest of value corresponding to Y and position 1 the value

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of Z at index 2.

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And finally the value of x at index 3 no index zero in this guess is reserved for the method parameter

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.

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And that's because this particular code fragment was part of the main method which we know has only

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a single parameter which is a String Theory.

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So if the code was inside some other static method that did not have any method parameters then our

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variable values y z on X would have been stored in expositions 0 1 and 2 respectively.

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So as you can see GBM uses are put in stack just like the way a CPO uses registers.

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So everything is done via the open stack.

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That's about stack frame.

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And we could also review these few simple bytecode instructions next to a very simple example.

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We will also explore a few other important bytecode instructions