# Run 1

Creating a simple virtual machine (VM) with an operand stack and a context stack for frames in Java involves multiple components that simulate the internals of how a stack-based VM operates.

Below is a basic example of such a VM:

```java
import java.util.Stack;

// Class to represent a Frame in the context stack
class Frame {
    private int[] localVariables; // Local variable array for the Frame
    private int returnAddress;    // Return address for the Frame

    public Frame(int localVariableSize) {
        localVariables = new int[localVariableSize];
    }

    public int getLocalVariable(int index) {
        return localVariables[index];
    }

    public void setLocalVariable(int index, int value) {
        localVariables[index] = value;
    }

    public int getReturnAddress() {
        return returnAddress;
    }

    public void setReturnAddress(int returnAddress) {
        this.returnAddress = returnAddress;
    }
}

// Simple OperandStack implementation
class OperandStack {
    private Stack<Integer> operandStack;

    public OperandStack() {
        operandStack = new Stack<>();
    }

    public void push(int value) {
        operandStack.push(value);
    }

    public int pop() {
        return operandStack.pop();
    }

    public int peek() {
        return operandStack.peek();
    }

    public boolean isEmpty() {
        return operandStack.isEmpty();
    }
}

// Simple Virtual Machine
class VirtualMachine {
    private Stack<Frame> contextStack;  // Context stack for function call frames
    private OperandStack operandStack;  // Operand stack for general operations

    public VirtualMachine() {
        contextStack = new Stack<>();
        operandStack = new OperandStack();
    }

    // Method to simulate 'push' instruction
    public void push(int value) {
        operandStack.push(value);
    }

    // Method to simulate 'pop' instruction
    public int pop() {
        return operandStack.pop();
    }

    // Method to simulate 'add' instruction
    public void add() {
        int value1 = operandStack.pop();
        int value2 = operandStack.pop();
        int sum = value1 + value2;
        operandStack.push(sum);
    }

    // Method to simulate a method call
    public void call(int address, int localVarSize) {
        Frame frame = new Frame(localVarSize);
        frame.setReturnAddress(address);
        contextStack.push(frame);
    }

    // Method to simulate a method return
    public void ret() {
        Frame currentFrame = contextStack.pop();
        int returnAddress = currentFrame.getReturnAddress();
        // Jump to return address (assuming that aspect of VM is implemented)
    }

    // Other VM instruction implementations can be added here...

    // Execute a simple predefined set of instructions
    public void execute() {
        // Simulated instruction sequence: push, push, add
        push(10);
        push(20);
        add();
        int result = pop();
        System.out.println("Execution Result: " + result); // Should print 30
    }
}

public class Main {
    public static void main(String[] args) {
        VirtualMachine vm = new VirtualMachine();
        vm.execute();
    }
}
```

### Explanation:

1. **Frame Class**: Represents a single frame in the context stack. It holds local variables and a return address.

2. **OperandStack Class**: A simple wrapper around a stack to represent the operand stack. This stack is where most of the computations happen (e.g., arithmetic operations).

3. **VirtualMachine Class**: Manages both the operand stack and the context stack. It includes basic instructions such as `push`, `pop`, and `add`, as well as a simple `call` and `ret` to simulate function calls.

4. **Main Class**: Just a basic entry point to test the VM by executing a small instruction sequence that adds two numbers.

### How it Works:
- In this VM, the stack-based operations occur on the operand stack.
- Context switching (like function calls and returns) involves manipulating frames on the context stack.
- The `execute` method in this example simulates pushing two integers onto the operand stack, adds them together, and then prints the result.

This is a simplified example and doesn't include features like instruction sets, loop control, or error handling, but it forms a basic foundation on which you can build a more complex virtual machine.