Stack Based Virtual Machine. It uses RPN syntax.

RPN.java

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.List;
import java.util.Scanner;
import java.util.Stack;

/**
 *
 */
public class RPN {
	private Stack<Integer> stack = new Stack<Integer>();

	private class StackFrame {
		public int ip;
		public HashMap<String, Integer> variables;

		public StackFrame(int ip, HashMap<String, Integer> variables) {
			this.ip = ip;
			this.variables = variables;
		}
	}

	private Stack<StackFrame> calls = new Stack<StackFrame>(); // call stack

	private HashMap<String, Integer> labels = new HashMap<String, Integer>();
	private HashMap<String, Integer> variables = new HashMap<String, Integer>();

	private String program;

	public RPN(String file) throws IOException {
		List<String> lines = Files.readAllLines(Paths.get(file), StandardCharsets.UTF_8); // http://stackoverflow.com/a/14169729/4004293
		StringBuilder sb = new StringBuilder();
		for (String line : lines) {
			line = line.replaceAll("^\\s*#.*$", "");
			if (line.length() > 0 && line.charAt(line.length() - 1) != ' ') {
				sb.append(line.trim()).append(' ');
			} else if (line.length() > 0){
				sb.append(line.trim()).append(' ');
			}
		}
		program = sb.toString();
		System.out.println(program);
	}

	public void eval() {
		String[] tokens = program.split("\\s(\\s)*");
		int ip = 0, f, s;
		String token;

		while (ip < tokens.length) {
			token = tokens[ip];
			if (token.matches("^label\\((.+)\\)$")) {
				String label = token.subSequence(
						token.indexOf('(') + 1,
						token.indexOf(')')
				).toString();
				labels.put(label, ip);
			}
			ip++;
		}

		ip = 0;
		while (ip < tokens.length) {
			token = tokens[ip++].trim();
			if (token.matches("[0-9]([0-9])*")) {
				stack.push(Integer.valueOf(token));
			} else {
				if (token.equalsIgnoreCase("+")) { /* ALU OP */
					s = stack.pop();
					f = stack.pop();
					stack.push(f + s);
				} else if (token.equalsIgnoreCase("-")) {
					s = stack.pop();
					f = stack.pop();
					stack.push(f - s);
				} else if (token.equalsIgnoreCase("*")) {
					s = stack.pop();
					f = stack.pop();
					stack.push(f * s);
				} else if (token.equalsIgnoreCase("/")) {
					s = stack.pop();
					f = stack.pop();
					stack.push(f / s);
				} else if (token.equalsIgnoreCase("%")) {
					s = stack.pop();
					f = stack.pop();
					stack.push(f % s);
				} else if (token.matches("^jmp\\((.+)\\)$")) { /* JUMP OP */
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					ip = labels.get(label);
				} else if (token.matches("^jz\\((.+)\\)$")) {
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					if (stack.pop() == 0) {
						ip = labels.get(label);
					}
				} else if (token.matches("^jnz\\((.+)\\)$")) {
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					if (stack.pop() != 0) {
						ip = labels.get(label);
					}
				} else if (token.matches("^jgz\\((.+)\\)$")) {
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					if (stack.pop() > 0) {
						ip = labels.get(label);
					}
				} else if (token.matches("^jgez\\((.+)\\)$")) {
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					if (stack.pop() >= 0) {
						ip = labels.get(label);
					}
				} else if (token.matches("^jlz\\((.+)\\)$")) {
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					if (stack.pop() < 0) {
						ip = labels.get(label);
					}
				} else if (token.matches("^jlez\\((.+)\\)$")) {
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					if (stack.pop() <= 0) {
						ip = labels.get(label);
					}
				} else if (token.matches("^call\\((.+)\\)$")) {
					String label = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					calls.push(new StackFrame(ip, new HashMap<String, Integer>(variables)));
					ip = labels.get(label);
				} else if (token.equalsIgnoreCase("ret")) {
					StackFrame frame = calls.pop();
					ip = frame.ip;
					variables = frame.variables;
				} else if (token.matches("^!var\\((.+)\\)$")) { /* VARS OP */
					String name = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					variables.put(name, stack.pop());
				} else if (token.matches("^var\\((.+)\\)$")) { /* VARS OP */
					String name = token.subSequence(
							token.indexOf('(') + 1,
							token.indexOf(')')
					).toString();
					stack.push(variables.get(name));
				} else if (token.equalsIgnoreCase(".")) { /* IO OP */
					// print the ASCII
					System.out.print((char) stack.pop().byteValue());
				} else if (token.equalsIgnoreCase(".num")) {
					// print int
					System.out.print(stack.pop());
				} else if (token.equalsIgnoreCase(",")) {
					// read number
					System.out.print("(int)>: ");
					stack.push(new Scanner(System.in).nextInt());
					System.out.println();
				} else if (token.equalsIgnoreCase("dup")) { /* STACK OP */
					stack.push(stack.peek());
				} else if (token.equalsIgnoreCase("drop")) {
					stack.pop();
				} else if (token.matches("^label\\((.+)\\)$")) { /* NO OP */
					// pseudo instruction
				} else {
					throw new UnsupportedOperationException(token);
				}
			}
		}
	}

	public static void main(String[] args) throws IOException {
		if (args.length == 1) {
			RPN rpn = new RPN(args[0]);
			rpn.eval();
		} else {
			System.out.println("USAGE: java RPN program");
		}
	}
}