对于一个具有层次节点关系的问题来说，如果您要剖析每一个节点，您可以使用Interpreter模式，直译器模式有些类似演算法中的个别击破方式，对每一个父节点我们剖析出其子节点组合，然而交给子节点剖析物件继续剖析，直到剖析至终端节点为止。
假设您要实作一个Interpreter，这个Interpreter可以直译您文字档中的程式，并依您自订的程式文法来执行程式，几个简单的程式如下：
PRINT dog SPACE
PRINT is SPACE
PRINT an SPACE
PRINT animai
END
您的这式程个会印出"dog is an animal"的文字，再来一个例子是：
REPEAT 2
LINEBREAK
PRINT dog
BREAK
END
END
这个程式要印出：
| ------------------------------ dog ------------------------------ dog |
您也可以任意的组合程式，例如：
PRINT begin
BREAK
REPEAT 3
REPEAT 2
PRINT dog SPACE
PRINT is SPACE
PRINT a SPACE
PRINT animal
BREAK
END
END
END
这个程式中的几个关键字是PROGRAM、PRINT、SPACE、BREAK、LINEBREAK、REPEAT、END，PROGRAM是表示程式开始，以END作结，PRINT可以印出一个无空白的字串，SPACE印出一个空白，BREAK是换行，而LINEBREAK是画一个直线并换行，REPEAT是回圈指令，可以指定回圈次数，以END作结。
观察程式，可以制定出以下的文法，如下：
<command list> ::= <command>* END
<command> ::= <repeat command> | <primitive command>
<repeat command> ::= REPEAT <number> <command list>
<primitive command> ::= PRINT <string>
| BREAK | SPACE | LINEBREAK
程式文法制定需要对程式进行语句分析与定义，在这边并不讨论这个课题，在程式中，command节点由primitive或repeat两个节点任意组合，一个command list节点则是零个以上的command节点组合而成，其中repeat还可以组合commandlist节点，这是组合模式的应用，可以在程式中组合巢状回圈。
在直译程式时，以读到PROGRAM作为开始节点，接下来我们剖析程式为command list 节点，并将它们丢给专门剖析commandlist的物件继续剖析，这个物件将之分析，看是不是有repeat command或primitivecommand节点，如果有就再往下交由专属物件进行剖析，如此层层剥开，并由专属物件负责剖析工作。
Interpreter模式的基本观念就如上所示，先来看看如何以程式实现剖析的过程，下面这个程式会剖析您的程式，并将程式加上对应的括号来将同一个区块组合起来，以表示它完成剖析之后的结果：
INode.java
public interface INode {
public void parse(Context context);
}
ProgramNode.java
// <program> ::= PROGRAM <command list>
public class ProgramNode implements INode {
private INode commandListNode;
public void parse(Context context) {
context.skipToken("PROGRAM");
commandListNode = new CommandListNode();
commandListNode.parse(context);
}
public String toString() {
return "[PROGRAM " + commandListNode + "]";
}
}
CommandListNode.java
import java.util.Vector;
// <command list> ::= <command>* END
public class CommandListNode implements INode {
private Vector list = new Vector();
public void parse(Context context) {
while (true) {
if (context.currentToken() == null) {
System.err.println("Missing 'END'");
break;
} else if (
context.currentToken().equals("END")) {
context.skipToken("END");
break;
} else {
INode commandNode = new CommandNode();
commandNode.parse(context);
list.add(commandNode);
}
}
}
public String toString() {
return "" + list;
}
}
CommandNode.java
// <command> ::= <repeat command> | <primitive command>
public class CommandNode implements INode {
private INode node;
public void parse(Context context) {
if (context.currentToken().equals("REPEAT")) {
node = new RepeatCommandNode();
node.parse(context);
} else {
node = new PrimitiveCommandNode();
node.parse(context);
}
}
public String toString() {
return node.toString();
}
}
RepeatCommandNode.java
public class RepeatCommandNode implements INode {
private int number;
private INode commandListNode;
public void parse(Context context) {
context.skipToken("REPEAT");
number = context.currentNumber();
context.nextToken();
commandListNode = new CommandListNode();
commandListNode.parse(context);
}
public String toString() {
return "[REPEAT " + number + " "
+ commandListNode + "]";
}
}
PrimitiveCommandNode.java
// <primitive command> ::= PRINT <string>
// | SPACE | BREAK | LINEBREAK
public class PrimitiveCommandNode implements INode {
private String name;
private String text;
public void parse(Context context) {
name = context.currentToken();
context.skipToken(name);
if (!name.equals("PRINT") && !name.equals("BREAK")
&& !name.equals("LINEBREAK")
&& !name.equals("SPACE")) {
System.err.println("Undefined Command");
}
if (name.equals("PRINT")) {
text = context.currentToken();
name += text;
context.nextToken();
}
}
public String toString() {
return name;
}
}
Context.java
import java.util.*;
public class Context {
private StringTokenizer tokenizer;
private String currentToken;
public Context(String text) {
tokenizer = new StringTokenizer(text);
nextToken();
}
public String nextToken() {
if (tokenizer.hasMoreTokens()) {
currentToken = tokenizer.nextToken();
} else {
currentToken = null;
}
return currentToken;
}
public String currentToken() {
return currentToken;
}
public void skipToken(String token) {
if (!token.equals(currentToken)) {
System.err.println("Warning: " + token +
" is expected, but " +
currentToken + " is found.");
}
nextToken();
}
public int currentNumber() {
int number = 0;
try {
number = Integer.parseInt(currentToken);
} catch (NumberFormatException e) {
System.err.println("Warning: " + e);
}
return number;
}
}
Main.java
import java.util.*;
import java.io.*;
public class Main {
public static void main(String[] args) {
try {
BufferedReader reader = new
BufferedReader(new FileReader(args[0]));
String text;
while ((text = reader.readLine()) != null) {
System.out.println("text = \"" +
text + "\"");
INode node = new ProgramNode();
node.parse(new Context(text));
System.out.println("node = " + node);
}
}
catch (ArrayIndexOutOfBoundsException e) {
System.err.println(
"Usage: java Main yourprogram.txt");
}
catch (Exception e) {
e.printStackTrace();
}
}
}
假设您的程式是这样写的：
program.txt
PROGRAM PRINT xxx END
PROGRAM REPEAT 4 PRINT xxx END END
PROGRAM REPEAT 4 PRINT xxx PRINT "yyy" END END
则执行Intrepreter程式之后会是：
$ java Main program.txt
text = "PROGRAM PRINT xxx END"
node = [PROGRAM [PRINTxxx]]
text = "PROGRAM REPEAT 4 PRINT xxx END END"
node = [PROGRAM [[REPEAT 4 [PRINTxxx]]]]
text = "PROGRAM REPEAT 4 PRINT xxx PRINT "yyy" END END"
node = [PROGRAM [[REPEAT 4 [PRINTxxx, PRINT"yyy"]]]]
这个范例程式基本上已经显示了直译器模式的工作原理，如何让程式直译之后能够工作，这待会再示范，先来看一下Intrepreter模式的 UML 类别结构图： 
TerminalExpression就像我们的primitive command，再剖析下去已经没有子节点了，而NonterminalExpression就像是repeat command，注意到其中也使用了组合模式，就如之前所说的，组合模式让可以递回的组合句子为更复杂的语句。
您已经会剖析句子了，接下来要如何让这个直译器真正工作，虽然程式中使用toString()来表示每一个节点的剖析结果，但事实上，这个程式也已经说明了如何让剖析的结果真正运作了，既然已经记录好剖析之后的语句顺序了，只要由上而下追踪剖析结果，就一定可以执行到 primitive command，且顺序符合自订的程式原始码的需求，这只要将toString()改为execute()，并作一些转发与重复执行的修改就可以了，直接来看程式会比较容易理解：
INode.java
public interface INode {
public void parse(Context context);
public void execute();
}
ProgramNode.java
// <program> ::= PROGRAM <command list>
public class ProgramNode implements INode {
private INode commandListNode;
public void parse(Context context) {
context.skipToken("PROGRAM");
commandListNode = new CommandListNode();
commandListNode.parse(context);
}
public void execute() {
commandListNode.execute();
}
public String toString() {
return "[PROGRAM " + commandListNode + "]";
}
}
CommandListNode.java
import java.util.*;
// <command list> ::= <command>* END
public class CommandListNode implements INode {
private Vector list = new Vector();
private INode commandNode;
public void parse(Context context) {
while (true) {
if (context.currentToken() == null) {
System.err.println("Missing 'END'");
break;
} else if(context.currentToken().equals("END")) {
context.skipToken("END");
break;
} else {
commandNode = new CommandNode();
commandNode.parse(context);
list.add(commandNode);
}
}
}
public void execute() {
Iterator it = list.iterator();
while (it.hasNext()) {
((CommandNode)it.next()).execute();
}
}
public String toString() {
return "" + list;
}
}
CommandNode.java
// <command> ::= <repeat command> | <primitive command>
public class CommandNode implements INode {
private INode node;
public void parse(Context context) {
if (context.currentToken().equals("REPEAT")) {
node = new RepeatCommandNode();
node.parse(context);
} else {
node = new PrimitiveCommandNode();
node.parse(context);
}
}
public void execute() {
node.execute();
}
public String toString() {
return node.toString();
}
}
PrimitiveCommandNode.java
// <primitive command> ::= PRINT <string>
// | SPACE | BREAK | LINEBREAK
public class PrimitiveCommandNode implements INode {
private String name;
private String text;
public void parse(Context context) {
name = context.currentToken();
context.skipToken(name);
if (!name.equals("PRINT") && !name.equals("BREAK")
&& !name.equals("LINEBREAK")
&& !name.equals("SPACE")) {
System.err.println("Undefined Command");
}
if (name.equals("PRINT")) {
text = context.currentToken();
context.nextToken();
}
}
public void execute() {
if(name.equals("PRINT"))
System.out.print(text);
else if(name.equals("SPACE"))
System.out.print(" ");
else if(name.equals("BREAK"))
System.out.println();
else if(name.equals("LINEBREAK"))
System.out.println(
"\n------------------------------");
}
public String toString() {
return name;
}
}
RepeatCommandNode.java
public class RepeatCommandNode implements INode {
private int number;
private INode commandListNode;
public void parse(Context context) {
context.skipToken("REPEAT");
number = context.currentNumber();
context.nextToken();
commandListNode = new CommandListNode();
commandListNode.parse(context);
}
public void execute() {
for(int i = 0; i < number; i++)
commandListNode.execute();
}
public String toString() {
return "[REPEAT " + number + " " +
commandListNode + "]";
}
}
Context.java
import java.util.*;
public class Context {
private StringTokenizer tokenizer;
private String currentToken;
public Context(String text) {
tokenizer = new StringTokenizer(text);
nextToken();
}
public String nextToken() {
if (tokenizer.hasMoreTokens()) {
currentToken = tokenizer.nextToken();
} else {
currentToken = null;
}
return currentToken;
}
public String currentToken() {
return currentToken;
}
public void skipToken(String token) {
if (!token.equals(currentToken)) {
System.err.println("Warning: " + token +
" is expected, but " +
currentToken + " is found.");
}
nextToken();
}
public int currentNumber() {
int number = 0;
try {
number = Integer.parseInt(currentToken);
} catch (NumberFormatException e) {
System.err.println("Warning: " + e);
}
return number;
}
}
Main.java
import java.util.*;
import java.io.*;
public class Main {
public static void main(String[] args) {
try {
BufferedReader reader = new BufferedReader(
new FileReader(args[0]));
String text;
while ((text = reader.readLine()) != null) {
System.out.println("text = \"" + text
+ "\"");
INode node = new ProgramNode();
node.parse(new Context(text));
node.execute();
}
}
catch (ArrayIndexOutOfBoundsException e) {
System.err.println(
"Useage: java Main yourprogram.txt");
}
catch (Exception e) {
e.printStackTrace();
}
}
}
假设您的直译程式稿是这么撰写的：
program.txt
PROGRAM REPEAT 4 LINEBREAK PRINT justin SPACE PRINT momor LINEBREAK END END
则程式执行的结果就是：
| $ java Main program.txt text = "PROGRAM REPEAT 4 LINEBREAK PRINT justin SPACE PRINT momor LINEBREAK END END" ------------------------------ justin momor ------------------------------ ------------------------------ ------------------------------ ------------------------------ |