解释器模式实例与解析---实例：数学运算解释器

现需要构造一个语言解释器，使得系统可以执行整数间的乘、除和求模运算。如用户输入表达式“3 * 4 / 2 % 4”，输出结果为2。使用解释器模式实现该功能

import java.util.*;

public class Calculator
{
	private String statement;
	private Node node;
    
    public void build(String statement)
    {
    	Node left=null,right=null;
    	Stack stack=new Stack();
    	
    	String[] statementArr=statement.split(" ");
    	
    	for(int i=0;i<statementArr.length;i++)
    	{	
    		if(statementArr[i].equalsIgnoreCase("*"))
    		{
    			left=(Node)stack.pop();
    		    int val=Integer.parseInt(statementArr[++i]);
    		    right=new ValueNode(val); 
    			stack.push(new MulNode(left,right));
    		}
    		else if(statementArr[i].equalsIgnoreCase("/"))
    		{
    			left=(Node)stack.pop();
    		    int val=Integer.parseInt(statementArr[++i]);
    		    right=new ValueNode(val); 
    			stack.push(new DivNode(left,right));    			
    		}
    		else if(statementArr[i].equalsIgnoreCase("%"))
    		{
    			left=(Node)stack.pop();
    		    int val=Integer.parseInt(statementArr[++i]);
    		    right=new ValueNode(val); 
    			stack.push(new ModNode(left,right));   			
    		}
    		else
    		{
    			stack.push(new ValueNode(Integer.parseInt(statementArr[i])));
    		}
    	}
    	this.node=(Node)stack.pop();
    }
	
	public int compute()
	{
		return node.interpret();
	}
}

public class Client
{
	public static void main(String args[])
	{
		String statement = "3 * 2 * 4 / 6 % 5";
		
		Calculator calculator = new Calculator();
		
		calculator.build(statement);
		
		int result = calculator.compute();
		
		System.out.println(statement + " = " + result);	
	}
}

public class DivNode extends SymbolNode
{
	public DivNode(Node left,Node right)
	{
		super(left,right);
	}
	
	public int interpret()
	{
		return super.left.interpret() / super.right.interpret();
	}
}

public class ModNode extends SymbolNode
{
	public ModNode(Node left,Node right)
	{
		super(left,right);
	}
	
	public int interpret()
	{
		return super.left.interpret() % super.right.interpret();
	}
}

public class MulNode extends SymbolNode
{
	public MulNode(Node left,Node right)
	{
		super(left,right);
	}
	
	public int interpret()
	{
		return super.left.interpret() * super.right.interpret();
	}
}

public interface Node
{
	public int interpret();
}

public abstract class SymbolNode implements Node
{
	protected Node left;
	protected Node right;
	
	public SymbolNode(Node left,Node right)
	{
		this.left=left;
		this.right=right;
	}
}

public class ValueNode implements Node
{
	private int value;
	
	public ValueNode(int value)
	{
		this.value=value;
	}
		
	public int interpret()
	{
		return this.value;
	}
}