java设计模式18_解释器模式

解释器模式

解释器模式提供了一种评估计算语言语法或表达式的方法，此模式用于SQL解析，符号处理引擎等

实现

创建一个接口Expression并且在具体的类实现这个Expression接口。 定义了一个TerminalExpression类，用作所讨论的上下文的主解释器。 其他的类 - OrExpression和AndExpression用于创建组合表达式

代码

package com.test;

//第1步,创建表达式接口
interface Expression {
public boolean interpret(String context);
}

// 第2步， 创建实现上述接口的具体类
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;
}
}

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);
}
}

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);
}
}

// 第3步，使用Expression类来创建规则，然后解析它们
public class Test {

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 Julise"));
}

// Rule: Robert and John are male
public static Expression getMaleExpression() {
Expression robert = new TerminalExpression("Robert");
Expression john = new TerminalExpression("John");
return new OrExpression(robert, john);
}

// Rule: Julie is a married women
public static Expression getMarriedWomanExpression() {
Expression julie = new TerminalExpression("Julie");
Expression married = new TerminalExpression("Married");
return new AndExpression(julie, married);
}
}

运行结果：

John is male? true
Julie is a married women? false