示例代码

抽象解释器

public interface Interpreter {
    int interpret();
}

具体解释器

• 都是对操作数或操作符的解释；

public class MultiInterpreter implements Interpreter {

    private Interpreter firstExpression, secondExpression;

    public MultiInterpreter(Interpreter firstExpression,
                            Interpreter secondExpression){
        this.firstExpression=firstExpression;
        this.secondExpression=secondExpression;
    }

    @Override
    public int interpret(){
        return this.firstExpression.interpret()
                *
                this.secondExpression.interpret();
    }

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

}

public class AddInterpreter implements Interpreter {

    private Interpreter firstExpression,secondExpression;

    public AddInterpreter(Interpreter firstExpression,
                          Interpreter secondExpression){
        this.firstExpression=firstExpression;
        this.secondExpression=secondExpression;
    }

    @Override
    public int interpret(){
        return this.firstExpression.interpret()
                +
                this.secondExpression.interpret();
    }

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

}

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 interpret(){
        return this.number;
    }

}

语法节解析器

• 对运算规则的解析，会用到具体解释器，具体解释器都是对操作数或操作符的解释；

public class GeelyExpressionParser {

    private Stack<Interpreter> stack = new Stack<Interpreter>();

    public int parse(String str) {
        String[] strItemArray = str.split(" ");
        for (String symbol : strItemArray) {
            if (!OperatorUtil.isOperator(symbol)) {
                Interpreter numberExpression = new NumberInterpreter(symbol);
                stack.push(numberExpression);
                System.out.println(String.format("入栈: %d", numberExpression.interpret()));
            } else {
                //是运算符号，可以计算
                Interpreter firstExpression = stack.pop();
                Interpreter secondExpression = stack.pop();
                System.out.println(String.format("出栈: %d 和 %d",
                        firstExpression.interpret(), secondExpression.interpret()));
                Interpreter operator = OperatorUtil.getExpressionObject(firstExpression, secondExpression, symbol);
                System.out.println(String.format("应用运算符: %s", operator));
                int result = operator.interpret();
                NumberInterpreter resultExpression = new NumberInterpreter(result);
                stack.push(resultExpression);
                System.out.println(String.format("阶段结果入栈: %d", resultExpression.interpret()));
            }
        }
        int result = stack.pop().interpret();
        return result;
    }
    
}

public class OperatorUtil {

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

    }

    public static Interpreter getExpressionObject(Interpreter firstExpression, Interpreter secondExpression, String symbol) {
        if (symbol.equals("+")) {
            return new AddInterpreter(firstExpression, secondExpression);
        } else if (symbol.equals("*")) {
            return new MultiInterpreter(firstExpression, secondExpression);
        }
        return null;
    }

}

客户端

public class Test {
    public static void main(String[] args) {
        String geelyInputStr="6 100 11 + *";
        GeelyExpressionParser expressionParser=new GeelyExpressionParser();
        int result = expressionParser.parse(geelyInputStr);
        System.out.println("解释器计算结果: "+result);
    }
}

输出：

入栈: 6
入栈: 100
入栈: 11
出栈: 11 和 100
应用运算符: +
阶段结果入栈: 111
出栈: 111 和 6
应用运算符: *
阶段结果入栈: 666
解释器计算结果: 666