3. 行为型模式 (11) 解释器模式

3. 行为型模式 (11) 解释器模式

解释器模式（Interpreter Pattern）实现了一个表达式接口，该接口解释一个特定的上下文。这种模式被用在 SQL 解析、符号处理引擎等。

优点：
1. 可扩展性比较好，灵活。
2. 增加了新的解释表达式的方式。
3. 易于实现简单文法。

缺点：
1. 可利用场景比较少。
2. 对于复杂的文法比较难维护。
3. 解释器模式会引起类膨胀。
4. 解释器模式采用递归调用方法。

1. 解释器模式

package com.andrew.pattern0311.interpreter.model01;
public interface Expression {
    public boolean interpret(String context);
}

package com.andrew.pattern0311.interpreter.model01;
public class TerminalExpression implements Expression {
    private String data;
    public TerminalExpression(String data) {
        this.data = data;
    }
    @Override
    public boolean interpret(String context) {
        if (context.contains(data)) {
            return true;
        }
        return false;
    }
}

package com.andrew.pattern0311.interpreter.model01;
public class OrExpression implements Expression {
    private Expression expr1 = null;
    private Expression expr2 = null;
    public OrExpression(Expression expr1, Expression expr2) {
        this.expr1 = expr1;
        this.expr2 = expr2;
    }
    @Override
    public boolean interpret(String context) {
        return expr1.interpret(context) || expr2.interpret(context);
    }
}

package com.andrew.pattern0311.interpreter.model01;
public class AndExpression implements Expression {
    private Expression expr1 = null;
    private Expression expr2 = null;
    public AndExpression(Expression expr1, Expression expr2) {
        this.expr1 = expr1;
        this.expr2 = expr2;
    }
    @Override
    public boolean interpret(String context) {
        return expr1.interpret(context) && expr2.interpret(context);
    }
}

package com.andrew.pattern0311.interpreter.model01;
/**
 * 1. 解释器模式
 * 
 * @author andrew
 * @date 2018/11/08
 */
public class Client {
    public static Expression getMaleExpression() {
        Expression robert = new TerminalExpression("Robert");
        Expression john = new TerminalExpression("John");
        return new OrExpression(robert, john);
    }
    public static Expression getMarriedWomanExpression() {
        Expression julie = new TerminalExpression("Julie");
        Expression married = new TerminalExpression("Married");
        return new AndExpression(julie, married);
    }
    public static void main(String[] args) {
        Expression isMale = getMaleExpression();
        Expression isMarriedWoman = getMarriedWomanExpression();
        System.out.println("John is male? " + isMale.interpret("John"));
        System.out.println("Julie is a married women? " + isMarriedWoman.interpret("Married Julie"));
    }
}
运行结果：
John is male? true
Julie is a married women? true