设计模式 - 解释器
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2023-12-01
解释器(Interpreter)
Intent
为语言创建解释器,通常由语言的语法和语法分析来定义。
Class Diagram
- TerminalExpression:终结符表达式,每个终结符都需要一个 TerminalExpression。
Context:上下文,包含解释器之外的一些全局信息。
Implementation
以下是一个规则检验器实现,具有 and 和 or 规则,通过规则可以构建一颗解析树,用来检验一个文本是否满足解析树定义的规则。
例如一颗解析树为 D And (A Or (B C)),文本 "D A" 满足该解析树定义的规则。
这里的 Context 指的是 String。
// java public abstract class Expression { public abstract boolean interpret(String str); }
// java public class TerminalExpression extends Expression { private String literal = null; public TerminalExpression(String str) { literal = str; } public boolean interpret(String str) { StringTokenizer st = new StringTokenizer(str); while (st.hasMoreTokens()) { String test = st.nextToken(); if (test.equals(literal)) { return true; } } return false; } }
// java public class AndExpression extends Expression { private Expression expression1 = null; private Expression expression2 = null; public AndExpression(Expression expression1, Expression expression2) { this.expression1 = expression1; this.expression2 = expression2; } public boolean interpret(String str) { return expression1.interpret(str) && expression2.interpret(str); } }
// java public class OrExpression extends Expression { private Expression expression1 = null; private Expression expression2 = null; public OrExpression(Expression expression1, Expression expression2) { this.expression1 = expression1; this.expression2 = expression2; } public boolean interpret(String str) { return expression1.interpret(str) || expression2.interpret(str); } }
// java public class Client { /** * 构建解析树 */ public static Expression buildInterpreterTree() { // Literal Expression terminal1 = new TerminalExpression("A"); Expression terminal2 = new TerminalExpression("B"); Expression terminal3 = new TerminalExpression("C"); Expression terminal4 = new TerminalExpression("D"); // B C Expression alternation1 = new OrExpression(terminal2, terminal3); // A Or (B C) Expression alternation2 = new OrExpression(terminal1, alternation1); // D And (A Or (B C)) return new AndExpression(terminal4, alternation2); } public static void main(String[] args) { Expression define = buildInterpreterTree(); String context1 = "D A"; String context2 = "A B"; System.out.println(define.interpret(context1)); System.out.println(define.interpret(context2)); } }
// html true false
JDK
- java.util.Pattern
- java.text.Normalizer
- All subclasses of java.text.Format
- javax.el.ELResolver