【Java 设计模式-源码】Bytecode 模式：使用自定义虚拟机解释指令

--- title: "Bytecode Pattern in Java: Interpreting Instructions with Custom Virtual Machines" shortTitle: Bytecode description: "Explore the Bytecode design pattern in Java, including its implementation, real-world examples, and use cases for efficient virtual machine instruction handling." category: Behavioral language: en tag: - Abstraction - Code simplification - Encapsulation - Game programming - Performance - Runtime --- ## Intent of Bytecode Design Pattern The Bytecode design pattern in Java allows encoding behavior as instructions for a virtual machine, making it a powerful tool in game development and other applications. ## Detailed Explanation of Bytecode Pattern with Real-World Examples Real-world example > An analogous real-world example of the Bytecode design pattern can be seen in the process of translating a book into multiple languages. Instead of directly translating the book from the original language into every other language, the book is first translated into a common intermediate language, like Esperanto. This intermediate version is easier to translate because it is simpler and more structured. Translators for each target language then translate from Esperanto into their specific languages. This approach ensures consistency, reduces errors, and simplifies the translation process, similar to how bytecode serves as an intermediate representation to optimize and facilitate the execution of high-level programming languages across different platforms. In plain words > Bytecode pattern enables behavior driven by data instead of code. [gameprogrammingpatterns.com](https://gameprogrammingpatterns.com/bytecode.html) documentation states: > An instruction set defines the low-level operations that can be performed. A series of instructions is encoded as a sequence of bytes. A virtual machine executes these instructions one at a time, using a stack for intermediate values. By combining instructions, complex high-level behavior can be defined. ## Programmatic Example of Bytecode Pattern in Java In this programmatic example, we show how the Bytecode pattern in Java can simplify the execution of complex virtual machine instructions through a well-defined set of operations. This real-world example demonstrates how the Bytecode design pattern in Java can streamline game programming by allowing wizards' behavior to be easily adjusted through bytecode instructions. A team is working on a new game where wizards battle against each other. The wizard behavior needs to be carefully adjusted and iterated hundreds of times through playtesting. It's not optimal to ask the programmer to make changes each time the game designer wants to vary the behavior, so the wizard behavior is implemented as a data-driven virtual machine. One of the most important game objects is the `Wizard` class. ```java @AllArgsConstructor @Setter @Getter @Slf4j public class Wizard { private int health; private int agility; private int wisdom; private int numberOfPlayedSounds; private int numberOfSpawnedParticles; public void playSound() { LOGGER.info("Playing sound"); numberOfPlayedSounds++; } public void spawnParticles() { LOGGER.info("Spawning particles"); numberOfSpawnedParticles++; } } ``` Next, we show the available instructions for our virtual machine. Each of the instructions has its own semantics on how it operates with the stack data. For example, the ADD instruction takes the top two items from the stack, adds them together and pushes the result to the stack. ```java @AllArgsConstructor @Getter public enum Instruction { LITERAL(1), // e.g. "LITERAL 0", push 0 to stack SET_HEALTH(2), // e.g. "SET_HEALTH", pop health and wizard number, call set health SET_WISDOM(3), // e.g. "SET_WISDOM", pop wisdom and wizard number, call set wisdom SET_AGILITY(4), // e.g. "SET_AGILITY", pop agility and wizard number, call set agility PLAY_SOUND(5), // e.g. "PLAY_SOUND", pop value as wizard number, call play sound SPAWN_PARTICLES(6), // e.g. "SPAWN_PARTICLES", pop value as wizard number, call spawn particles GET_HEALTH(7), // e.g. "GET_HEALTH", pop value as wizard number, push wizard's health GET_AGILITY(8), // e.g. "GET_AGILITY", pop value as wizard number, push wizard's agility GET_WISDOM(9), // e.g. "GET_WISDOM", pop value as wizard number, push wizard's wisdom ADD(10), // e.g. "ADD", pop 2 values, push their sum DIVIDE(11); // e.g. "DIVIDE", pop 2 values, push their division // Other properties and methods... } ``` At the heart of our example is the `VirtualMachine` class. It takes instructions as input and executes them to provide the game object behavior. ```java @Getter @Slf4j public class VirtualMachine { private final Stack<Integer> stack = new Stack<>(); private final Wizard[] wizards = new Wizard[2]; public VirtualMachine() { wizards[0] = new Wizard(randomInt(3, 32), randomInt(3, 32), randomInt(3, 32), 0, 0); wizards[1] = new Wizard(randomInt(3, 32), randomInt(3, 32), randomInt(3, 32), 0, 0); } public VirtualMachine(Wizard wizard1, Wizard wizard2) { wizards[0] = wizard1; wizards[1] = wizard2; } public void execute(int[] bytecode) { for (var i = 0; i < bytecode.length; i++) { Instruction instruction = Instruction.getInstruction(bytecode[i]); switch (instruction) { case LITERAL: // Read the next byte from the bytecode. int value = bytecode[++i]; // Push the next value to stack stack.push(value); break; case SET_AGILITY: var amount = stack.pop(); var wizard = stack.pop(); setAgility(wizard, amount); break; case SET_WISDOM: amount = stack.pop(); wizard = stack.pop(); setWisdom(wizard, amount); break; case SET_HEALTH: amount = stack.pop(); wizard = stack.pop(); setHealth(wizard, amount); break; case GET_HEALTH: wizard = stack.pop(); stack.push(getHealth(wizard)); break; case GET_AGILITY: wizard = stack.pop(); stack.push(getAgility(wizard)); break; case GET_WISDOM: wizard = stack.pop(); stack.push(getWisdom(wizard)); break; case ADD: var a = stack.pop(); var b = stack.pop(); stack.push(a + b); break; case DIVIDE: a = stack.pop(); b = stack.pop(); stack.push(b / a); break; case PLAY_SOUND: wizard = stack.pop(); getWizards()[wizard].playSound(); break; case SPAWN_PARTICLES: wizard = stack.pop(); getWizards()[wizard].spawnParticles(); break; default: throw new IllegalArgumentException("Invalid instruction value"); } LOGGER.info("Executed " + instruction.name() + ", Stack contains " + getStack()); } } public void setHealth(int wizard, int amo