设计模式-解释器模式示例（二）

public class Context {
    private Map<String, Integer> variables = new HashMap<>();

    public void assign(String variable, int value) {
        variables.put(variable, value);
    }

    public int getValue(String variable) {
        return variables.get(variable);
    }
}

public class Client {
    public static void main(String[] args) {
        Context context = new Context();

        Expression expr1 = new NumberExpression(10);
        Expression expr2 = new NumberExpression(20);

        context.assign("a", 10);
        context.assign("b", 20);

        Expression expr3 = new MultiplyExpression(new NumberExpression(2), new NumberExpression(3));
        Expression expr4 = new AddExpression(new NumberExpression(5), new NumberExpression(10));
        Expression expr5 = new SubtractExpression(expr2, expr1);
        Expression expr6 = new DivideExpression(expr2, expr1);

        System.out.println("a = " + context.getValue("a"));
        System.out.println("b = " + context.getValue("b"));
        System.out.println("2 * 3 = " + expr3.interpret(context));
        System.out.println("5 + 10 = " + expr4.interpret(context));
        System.out.println("20 - 10 = " + expr5.interpret(context));
        System.out.println("20 / 10 = " + expr6.interpret(context));
    }
}

a = 10
b = 20
2 * 3 = 6
5 + 10 = 15
20 - 10 = 10
20 / 10 = 2