用Lambda简化枚举

(Updated: )

需求场景

解释器需要能够解释执行一些预设的指令，为了避免字符串判断+switch/case的丑陋写法，选择使用枚举类实现

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// Operation.java
public enum Operation {
  op1 ("op1") {
    public void exec () {
      //...
    }
  },
  op2 ("op2") {
    public void exec () {
      //...
    }
  };
  
  private String type;
  Operation(String type) { this.type = type; }
  
  abstract public Data exec ();
}

用Lambda改写

使用Lambda需要一个只有一个抽象函数的接口

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// Executable.java
public interface Executable {
  void exec (Parser parser);
}
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// MOperation.java
public enum MOperation implements Executable {
  op1("op1", (Parser parser) -> {
    //...
  }),
  op2("op2", (Parser parser) -> {
    //...
  });
  
  private final String type;
  private final Executable executor;
  MOperation(String type, Executable executor) {
    this.type = type;
    this.executor = executor;
  }
  
  @Override
  public Token exec (Parser parser) throws Exception {
    return executor.exec(parser);
  }
}

改写之后，不仅枚举部分的代码更简洁直观，而且可以通过executor传参，比之前更灵活

参考资料

java - Lambdas in the classical Operation enum example - Stack Overflow