Design Pattern 简明教程
Design Patterns - Interpreter Pattern
解释器模式提供了一种评估语言语法或表达式的途径。这类模式属于行为型模式。本模式需要实现一个表达式接口，描述一个特定上下文的解析方式。本模式常用于 SQL 解析、符号处理引擎等场景。
Implementation
我们将创建一个表达式接口和实现该表达接口的具体类。类 TerminalExpression 被定义为问题的上下文的主解释器。其他类 OrExpression、AndExpression 用于创建组合表达式。
我们的演示类 InterpreterPatternDemo 将使用 Expression 类创建规则，并演示如何解析表达式。
Step 1
创建一个表达式接口。
Expression.java
public interface Expression {
public boolean interpret(String context);
}Step 2
创建实现上述接口的具体类。
TerminalExpression.java
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;
}
}OrExpression.java
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);
}
}AndExpression.java
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);
}
}Step 3
InterpreterPatternDemo 使用 Expression 类来创建规则并解释它们。
InterpreterPatternDemo.java
public class InterpreterPatternDemo {
//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);
}
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"));
}
}