Question

我想要解析一个算术表达式，在解析后我应该有一个带有值和运算符的bynari树，之后我想用访问者模式进行遍历并得到结果。

我已经解析并构建了树，但每个Node都有足够多的变量：

public class Nod {

public float value = 0;
public String operator =" ";
public int priorityOrder = 0;

public Nod left = null;
public Nod right = null;


public Nod(String operator,int priorityOrder){
    this.priorityOrder = priorityOrder;
    this.operator = operator;
}

public Nod(float value){
    this.value = value;
}

public void setNodLR(Nod left, Nod right){
    this.left  = left;
    this.right = right;
}
}

public class ExpParser {


   Stack<Nod> stackRezults = new Stack<Nod>();
   Stack<Nod> stackOperators = new Stack<Nod>();
   ....
   // after all instructions .. stackRezults.peek()  will give me the root of tree 

//without visitor pattern..
public float Evaluate(Nod node){
       if( node.right == null && node.left == null)
          return node.value;

       float leftValue = Evaluate(node.left);
       float rightValue = Evaluate(node.right);

       switch(node.operator){

         case "+" :  
                    return leftValue + rightValue;
                    break;
          // same for others..
       }

}

}

//我有一种感觉我无法使用访客模式与我当前的树

我希望每个节点都有变量值或运算符不是两者兼而有之，我已经尝试过泛型......

 public class Nod<T>  {

T data ;

Nod<T> left  = null;
Nod<T> right = null;

public Nod(T data){
    this.data = data;
}

public <T> void setNodLR(Nod<T> left , Nod<T> right){
    this.left =  left;
    this.right = right;
}

}
从这里我已经死了..我甚至不能在这个Nod做最后的评估功能..，

//我在这里试了一下

     public class Expval {

public <T> float  evalExp(String expression){

    // i was trying to check if it works.. for expression : 3 + 2
    String Vexp[] = expression.split(" ");


    Nod<String> root = new Nod<>(Vexp[1]); // here is  +
    Nod<Float> left =  new Nod<>( Float.parseFloat(Vexp[0]) ); // here is 3
    Nod<Float> right  = new Nod<>(Float.parseFloat(Vexp[2]) ); // here is 2
    Radi.setNodRL(left, right); 



    return 0f;
}

  public <T> float Evaluate (Nod<T> Rad){
    if(Rad.left == null && Rad.right == null)
        return (float)Rad.data; // here i got a error
                                            // Can not cast from T to float

    float leftValue = Evaluate(Rad.left);
            float rightValue = Evaluate(Rad.right); 
        // and here 2 wornings Uncheked invocation Evaluate(Nod) of the generic method 
          Evaluate(Nod<T>)   of type ExpParser                              
         // The expression of type Nod needs unchecked conversion to conform to Nod<Object>


    switch((String)Rad.data){

    case "+" :
                return leftValue + rightValue;// if i change float to T i    will get here error
                break;
    }
}

  public <T> float Evaluate(Nod<T> node ){
        // how can  i do this ?
        // I mean  how do i  know if my node contains a string or value
  }

如果我走错路告诉我......如果我想和访客一起做，那么树应该是不同的？他们应该如何访问方法，让EvalVisitor类实现Visitor？

解析算术表达式并构建树，并使用访问者模式进行遍历

0 个答案: