package gep.num;import gep.Expression;import java.util.ArrayList;import java.util.List;/** * 自然對(duì)數(shù)函數(shù)表達(dá)式 */public class Log implements NExpression{	public static final char code = 'L';	public static final int arity = 1;		private NExpression left;		public char getCode()	{		return code;	}	public int getArity()	{		return arity;	}	public void addChild(Expression child)	{		if (left==null)		{			left = (NExpression) child;			return; 		}				throw new IllegalStateException("ADD_CHILD_ERROR");	}	public double evaluate()	{		double answer = Math.log(left.evaluate());		if (Double.isNaN(answer)) throw new RuntimeException("error on log");		return answer;	}		public String toString()	{		return "Log[" + left + "]";	}	public List getChildren()	{		List children = new ArrayList();		children.add(left);				return children;	}}