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notes/设计模式 - 解释器.md

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+## 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。
+
+<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/2b125bcd-1b36-43be-9b78-d90b076be549.png"/> </div><br>
+
+### 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](http://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html)
+- [java.text.Normalizer](http://docs.oracle.com/javase/8/docs/api/java/text/Normalizer.html)
+- All subclasses of [java.text.Format](http://docs.oracle.com/javase/8/docs/api/java/text/Format.html)
+- [javax.el.ELResolver](http://docs.oracle.com/javaee/7/api/javax/el/ELResolver.html)
+
+
+
+
+
+
+<div align="center"><img width="320px" src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/githubio/公众号二维码-2.png"></img></div>