解释器模式

这是设计模式最后一篇，迟迟没有写。听到这个名字可能会想到解释型语言，学习编译倒也可以参考一下这个。这个在实际工作中用的很少，直接上实现加减乘除的代码吧

public class Interpreter {    interface Expression {        int interpret(Context context);    }    //终结符表达式(Terminal Expression)    static class Constant implements Expression {        private int i;        public Constant(int i) {            this.i = i;        }        @Override        public int interpret(Context context) {            return i;        }    }    static class Variable implements Expression {        @Override        public int interpret(Context context) {            return context.LookupValue(this);        }    }    //非终结符表达式(Nonterminal Expression)    static class Add implements Expression {        private Expression left, right;        public Add(Expression left, Expression right) {            this.left = left;            this.right = right;        }        @Override        public int interpret(Context context) {            return left.interpret(context) + right.interpret(context);        }    }    static class Sub implements Expression {        private Expression left, right;        public Sub(Expression left, Expression right) {            this.left = left;            this.right = right;        }        @Override        public int interpret(Context context) {            return left.interpret(context) - right.interpret(context);        }    }    static class Mul implements Expression {        private Expression left, right;        public Mul(Expression left, Expression right) {            this.left = left;            this.right = right;        }        @Override        public int interpret(Context context) {            return left.interpret(context) * right.interpret(context);        }    }    static class Div implements Expression {        private Expression left, right;        public Div(Expression left, Expression right) {            this.left = left;            this.right = right;        }        @Override        public int interpret(Context context) {            return left.interpret(context) / right.interpret(context);        }    }    //环境(Context)角色，保存一些值    static class Context {        private Map valueMap = new HashMap<>();        public void addValue(Variable x, int y) {            valueMap.put(x, y);        }        public int LookupValue(Variable x) {            return (int) valueMap.get(x);        }    }    public static void main(String[] args) {        Context context = new Context();        Variable a = new Variable();        Variable b = new Variable();        Constant c = new Constant(15000);        context.addValue(a, 14);        context.addValue(b, 10000);        Expression expression =  new Add(new Sub(c, b), a);        System.out.println("Result = " + expression.interpret(context));    }}输出：Result = 5014

核心就两个：环境对象、表达式。写完了，很多地方思考的应该都不是太清楚。以后可能要持续更新，好的东西都是打磨出来的。等自己再上一个台阶也会想想当时的思维，写下来也有个记录还是挺好的。

觉得容易理解的话面向对象的23种设计模式点这里