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Java设计模式:解释器模式

05 Oct 2014

注:本文为译文,原文出处java-design-patterns-in-stories

在某些场景需要被解释的情况下, 我们通常使用解释器模式. 接下来的例子是一个很简单的解释器的实现. 它所做的就是将字母”a”与”b”解析为”1”和”2”.

类图

interpreter pattern class diagram

注: 图中也展示了依赖从而是结构更易于理解.

Java代码

class Context {

    private String input;
    private String output;

    public Context(String input) {
        this.input = input;
        this.output = "";
    }

    public String getInput() {
        return input;
    }
    public void setInput(String input) {
        this.input = input;
    }
    public String getOutput() {
        return output;
    }
    public void setOutput(String output) {
        this.output = output;
    }
}

abstract class Expression {
    public abstract void interpret(Context context);
}

class AExpression extends Expression {
    public void interpret(Context context) {
        System.out.println("a expression");
        String input = context.getInput();

        context.setInput(input.substring(1));
        context.setOutput(context.getOutput()+ "1");
    }

}

class BExpression extends Expression {
    public void interpret(Context context) {
        System.out.println("b expression");
        String input = context.getInput();

        context.setInput(input.substring(1));
        context.setOutput(context.getOutput()+ "2");
    }
}

public class TestInterpreter {
    public static void main(String[] args) {
           String str = "ab";
           Context context = new Context(str);

           List<Expression> list = new ArrayList<Expression>();
           list.add(new AExpression());
           list.add(new BExpression());

           for(Expression ex : list) {
               ex.interpret(context);

           }

           System.out.println(context.getOutput());
       }
}

解释器模式在JDK中的应用

java.util.Pattern

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