递归向下解析算术表达式(三)

本例代码下载:https://files.cnblogs.com/files/heyang78/MathAnalyzer2-20200524-1.zip

较原有版本,是多了Node类和TreeBuilder类,二者用于构建表达式树:

Node类:

package com.heyang;

public class Node {
    private String text;
    private Node leftChild;
    private Node rightChild;
    
    public Node() {
        this("");
    }
    
    public Node(String text) {
        this.text=text;
    }
    
    public String getText() {
        return text;
    }
    public void setText(String text) {
        this.text = text;
    }
    public Node getLeftChild() {
        return leftChild;
    }
    public void setLeftChild(Node leftChild) {
        this.leftChild = leftChild;
    }
    public Node getRightChild() {
        return rightChild;
    }
    public void setRightChild(Node rightChild) {
        this.rightChild = rightChild;
    }
}

TreeBuilder类:

package com.heyang;

import java.util.List;

public class TreeBuilder {
    private List<Token> tokens;
    private int tokenIdx;
    private Node root;
    
    public TreeBuilder(List<Token> tokens)  throws AnalyzerExp{
        this.tokens=tokens;
        this.tokenIdx=0;
        
        root=parse_expression();
    }
    
    public Node getRoot() {
        return root;
    }
    
    private Token fetchToken() {
        if(tokenIdx>=tokens.size()) {
            return null;
        }else {
            Token t=tokens.get(tokenIdx);
            tokenIdx++;
            return t;
        }        
    }
    
    private void returnToken() {
        if(tokenIdx>0) {
            tokenIdx--;
        }
    }
    
    private Node parse_expression() throws AnalyzerExp{
        Node left,right;
        Token currentToken;
        
        left=parse_term();
        for(;;) {
            currentToken=fetchToken();
            if(currentToken==null) {
                return left;
            }
            
            if(currentToken.getType()!=Token.TYPE_PLUS && currentToken.getType()!=Token.TYPE_MINUS) {
                returnToken();
                break;
            }
            
            right=parse_term();
            
            Node plusMinusNode=new Node(currentToken.getText());
            plusMinusNode.setLeftChild(left);
            plusMinusNode.setRightChild(right);
            left=plusMinusNode;
        }
        
        return left;
    }
    
    private Node parse_term() throws AnalyzerExp{
        Node left,right;
        Token currentToken;
        
        left=parse_primary_exp();
        for(;;) {
            currentToken=fetchToken();
            if(currentToken==null) {
                return left;
            }
            
            if(currentToken.getType()!=Token.TYPE_MULTI && currentToken.getType()!=Token.TYPE_DIVIDE) {
                returnToken();
                break;
            }
            
            right=parse_primary_exp();
            
            Node multiDivideNode=new Node(currentToken.getText());
            multiDivideNode.setLeftChild(left);
            multiDivideNode.setRightChild(right);
            left= multiDivideNode;
        }
        
        return left;
    }
    
    private Node parse_primary_exp() throws AnalyzerExp{
        Token currToken;
        
        currToken=fetchToken();
        if(currToken==null) {
            return null;
        }
        
        if(currToken.getType()==Token.TYPE_DIGITAL) {
            return new Node(currToken.getText());
        }else if(currToken.getType()==Token.TYPE_LEFT_PAREN){
            Node retval=parse_expression();
            
            currToken=fetchToken();
            if(currToken==null) {
                return retval;
            }
            
            if(currToken.getType()!=Token.TYPE_RIGHT_PAREN) {
                throw new AnalyzerExp("missing )");
            }
            
            return retval;
        }else {
            throw new AnalyzerExp(currToken+" should be a digital.");
        }
    }
}

解析效果:

1+2+3=6.0
      +      
    /       
  +       3  
 /          
1   2        
1+2+3+4=10.0
            +            
         /              
      +           4      
    /                   
  +       3              
 /                      
1   2                    
1+2+3+4+5=15.0
                        +                        
                    /                           
                +               5                
             /                                  
          +           4                          
        /                                       
      +       3                                  
     /                                          
    1   2                                        
1+(2+3)*4=21.0
            +            
         /              
      1           *      
                /       
              +       4  
             /          
            2   3        
1+(2+3)*4+5=26.0
                        +                        
                    /                           
                +               5                
             /                                  
          1           *                          
                    /                           
                  +       4                      
                 /                              
                2   3                            

--2020年5月24日--