标题：Java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。 这种类型的模式属于行为模式。 这种模式涉及实现一个表达式接口，它告诉解释一个指定的上下文。 此模式用于SQL解析，符号处理引擎等。

实现示例

我们将创建一个接口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。

InterpreterPatternDemo这是一个演示类，将使用Expression类来创建规则并演示表达式的解析。

实现解释器模式的结构如下图所示 -

第1步

创建表达式接口 -
Expression.java

复制纯文本复制

public interface Expression {
   public boolean interpret(String context);
}
Java

public interface Expression {
   public boolean interpret(String context);
}
Java

第2步

创建实现上述接口的具体类。
TerminalExpression.java

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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;
   }
}
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;
   }
}
Java

OrExpression.java

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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);
   }
}
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);
   }
}
Java

AndExpression.java

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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);
   }
}
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);
   }
}
Java

第3步

reterPatternDemo使用Expression类来创建规则，然后解析它们。

InterpreterPatternDemo.java

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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"));
   }
}
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"));
   }
}
Java

第4步

验证输出 -

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

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