解释器模式

1. 定义与类型

• 定义：给定一个语言，定义它的文法的一种示意，并定义一个解释器，这个解释器应用该示意来解释语言中的句子
• 为了解释一种语言，而为语言创立的解释器
• 类型：行为型

2. 实用场景

• 某个特定类型问题产生频率足够高

3. 长处

• 语法由很多类示意, 容易扭转及扩大此语言

4. 毛病

• 当语法规定数目太多，减少了零碎复杂度

5. 相干设计模式

• 解释器模式和适配器模式

6.Coding

• 创立解释器顶级接口

public interface Interpreter {int interpreter();
}

• 解释器的相干实现类

public class AddInterpreter implements Interpreter{
    private Interpreter firstExpression,secondExpression;

    public AddInterpreter(Interpreter firstExpression,Interpreter secondExpression){
        this.firstExpression = firstExpression;
        this.secondExpression = secondExpression;
    }
    @Override
    public int interpreter() {return this.firstExpression.interpreter() + this.secondExpression.interpreter();}

    @Override
    public String toString() {return "+";}
}

public class MultiInterpreter implements Interpreter{
    private Interpreter firstExpression,secondExpression;

    public MultiInterpreter(Interpreter firstExpression,Interpreter secondExpression){
        this.firstExpression = firstExpression;
        this.secondExpression = secondExpression;
    }
    @Override
    public int interpreter() {return this.firstExpression.interpreter() * this.secondExpression.interpreter();}

    @Override
    public String toString() {return "*";}
}

• 创立数字解释器，用于解决入参

public class NumberInterpreter implements Interpreter {
    private int number;

    public NumberInterpreter(int number) {this.number = number;}

    public NumberInterpreter(String number) {this.number = Integer.parseInt(number);
    }

    @Override
    public int interpreter() {return this.number;}
}

• 简略实现一个工具类

public class OperatorUtil {public static boolean isOperator(String symbol) {return (symbol.equals("+") || symbol.equals("*"));
    }

    public static Interpreter getExpressionObjects(Interpreter firstInterpreter, Interpreter secondInterpreter, String symbol) {if ("+".equals(symbol)) {return new AddInterpreter(firstInterpreter, secondInterpreter);
        } else if ("*".equals(symbol)) {return new MultiInterpreter(firstInterpreter, secondInterpreter);
        }
        return null;
    }
}

• 自定义一个解释器语法

public class QchExpressionParser {private Stack<Interpreter> stack = new Stack<>();

    public int parse(String str) {String[] strArray = str.split(" ");
        for (String item : strArray) {if (!OperatorUtil.isOperator(item)) {NumberInterpreter numberInterpreter = new NumberInterpreter(item);
                stack.push(numberInterpreter);
                System.out.println(String.format("入栈：%d", numberInterpreter.interpreter()));
            } else {Interpreter firstInterpreter = stack.pop();
                Interpreter secondInterpreter = stack.pop();
                System.out.println(String.format("出栈:%d 和 %d", firstInterpreter.interpreter(), secondInterpreter.interpreter()));
                Interpreter expressionObjects = OperatorUtil.getExpressionObjects(firstInterpreter, secondInterpreter, item);
                System.out.println(String.format("利用运算符: %s", expressionObjects.interpreter()));
                int result = expressionObjects.interpreter();
                NumberInterpreter numberInterpreter = new NumberInterpreter(result);
                stack.push(numberInterpreter);
                System.out.println(String.format("阶段后果入栈:%d", result));
            }
        }
        int result = stack.pop().interpreter();
        return result;
    }
}

• Test 测试类

public class Test {public static void main(String[] args) {
        String geelyInputStr = "6 100 11 + *";
        QchExpressionParser expressionParser = new QchExpressionParser();
        int parse = expressionParser.parse(geelyInputStr);
        System.out.println("解释器执行后果为:"+parse);
    }
}

• 控制台打印

7. 源码

• Spring 框架中的应用

public class TestForSpring {public static void main(String[] args) {ExpressionParser parser = new SpelExpressionParser();
      
        Expression expression = parser.parseExpression("100 + 11 * 6");
      
        int result = (int)expression.getValue();
      
        System.out.println(result);
    }

}

• debug 看下源码

  • 这个办法解决咱们的表达式

  • 最初