java设计模式适配器模式_Java解释器设计模式

java设计模式适配器模式

Interpreter design pattern is one of the behavioral design pattern. Interpreter pattern is used to defines a grammatical representation for a language and provides an interpreter to deal with this grammar.

口译设计模式是行为设计模式之一 。解释器模式用于定义一种语言的语法表示形式，并提供解释器来处理这种语法。

口译员设计模式 (Interpreter Design Pattern)

The best example of interpreter design pattern is java compiler that interprets the java source code into byte code that is understandable by JVM. Google Translator is also an example of interpreter pattern where the input can be in any language and we can get the output interpreted in another language.

解释器设计模式的最佳示例是Java编译器，它将Java源代码解释为JVM可以理解的字节代码。 Google Translator也是解释器模式的一个示例，其中输入可以使用任何语言，而我们可以使用另一种语言来解释输出。

解释器模式示例 (Interpreter Pattern Example)

To implement interpreter pattern, we need to create Interpreter context engine that will do the interpretation work.

为了实现解释器模式，我们需要创建解释器上下文引擎来完成解释工作。

Then we need to create different Expression implementations that will consume the functionalities provided by the interpreter context.

然后，我们需要创建不同的Expression实现，这些实现将使用解释器上下文提供的功能。

Finally we need to create the client that will take the input from user and decide which Expression to use and then generate output for the user.

最后，我们需要创建一个客户端，它将从用户那里获取输入，并确定要使用哪个Expression，然后为用户生成输出。

Let’s understand this with an example where the user input will be of two forms – “<Number> in Binary” or “<Number> in Hexadecimal.” Our interpreter client should return it in format “<Number> in Binary= <Number_Binary_String>” and “<Number> in Hexadecimal= <Number_Binary_String>” respectively.

让我们以一个示例来了解这一点，其中用户输入将采用两种形式–“ <Number> in Binary ”或“ <Number> in Hexadecimal 。” 我们的解释器客户端应分别以“ <Number> in Binary= <Number_Binary_String> <Number> in Hexadecimal= <Number_Binary_String> ”格式返回它。

Our first step will be to write the Interpreter context class that will do the actual interpretation.

我们的第一步将是编写解释器上下文类，该类将进行实际的解释。

package com.journaldev.design.interpreter;public class InterpreterContext {public String getBinaryFormat(int i){return Integer.toBinaryString(i);}public String getHexadecimalFormat(int i){return Integer.toHexString(i);}
}

Now we need to create different types of Expressions that will consume the interpreter context class.

现在，我们需要创建不同类型的表达式，这些表达式将使用解释器上下文类。

package com.journaldev.design.interpreter;public interface Expression {String interpret(InterpreterContext ic);
}

We will have two expression implementations, one to convert int to binary and other to convert int to hexadecimal format.

我们将有两种表达式实现，一种将int转换为二进制，另一种将int转换为十六进制格式。

package com.journaldev.design.interpreter;public class IntToBinaryExpression implements Expression {private int i;public IntToBinaryExpression(int c){this.i=c;}@Overridepublic String interpret(InterpreterContext ic) {return ic.getBinaryFormat(this.i);}}

package com.journaldev.design.interpreter;public class IntToHexExpression implements Expression {private int i;public IntToHexExpression(int c){this.i=c;}@Overridepublic String interpret(InterpreterContext ic) {return ic.getHexadecimalFormat(i);}}

Now we can create our client application that will have the logic to parse the user input and pass it to correct expression and then use the output to generate the user response.

现在，我们可以创建客户端应用程序，该应用程序将具有逻辑来解析用户输入并将其传递给正确的表达式，然后使用输出生成用户响应。

package com.journaldev.design.interpreter;public class InterpreterClient {public InterpreterContext ic;public InterpreterClient(InterpreterContext i){this.ic=i;}public String interpret(String str){Expression exp = null;//create rules for expressionsif(str.contains("Hexadecimal")){exp=new IntToHexExpression(Integer.parseInt(str.substring(0,str.indexOf(" "))));}else if(str.contains("Binary")){exp=new IntToBinaryExpression(Integer.parseInt(str.substring(0,str.indexOf(" "))));}else return str;return exp.interpret(ic);}public static void main(String args[]){String str1 = "28 in Binary";String str2 = "28 in Hexadecimal";InterpreterClient ec = new InterpreterClient(new InterpreterContext());System.out.println(str1+"= "+ec.interpret(str1));System.out.println(str2+"= "+ec.interpret(str2));}
}

The client also has a main method for testing purpose, when we run above we get following output:

客户端还有一个主要的测试方法，当我们在上面运行时，得到以下输出：

28 in Binary= 11100
28 in Hexadecimal= 1c

口译员设计模式示例类图 (Interpreter Design Pattern Example Class Diagram)

关于解释器模式的要点 (Important Points about Interpreter pattern)

Interpreter pattern can be used when we can create a syntax tree for the grammar we have.当我们可以为已有的语法创建语法树时，可以使用解释器模式。
Interpreter design pattern requires a lot of error checking and a lot of expressions and code to evaluate them. It gets complicated when the grammar becomes more complicated and hence hard to maintain and provide efficiency.解释器设计模式需要进行大量的错误检查，并需要大量的表达式和代码来对其进行评估。当语法变得更加复杂，因此难以维护和提供效率时，它将变得复杂。
java.util.Pattern and subclasses of java.text.Format are some of the examples of interpreter pattern used in JDK.java.util.Pattern和java.text.Format子类是JDK中使用的解释器模式的一些示例。

翻译自: https://www.journaldev.com/1635/interpreter-design-pattern-java

java设计模式适配器模式