stack.java

进行四则运算"+-*/^ ",并可以处理简单变量"AB",并且具备可扩展性.

public class Stack<T> {   
    public StackNode<T> stackTop;   
    public int count;   
    public void push(T info) {   
        StackNode<T> node = new StackNode<T>();   
        node.info = info;   
        node.link = stackTop;   
        stackTop = node;   
        count++;   
    }    
       
    public void pop() {   
        if(stackTop == null) {   
            System.out.println("null stack");   
        } else {   
            stackTop = stackTop.link;   
            count--;   
        }   
  
    }   
       
    public boolean isEmpty() {   
        return count == 0;   
    }   
       
    public T top() {   
        if(stackTop == null) {   
            return null;   
        }   
        return stackTop.info;   
    }   
       
    public String toString(){   
        Stack<T> other = new Stack<T>();   
        while(count != 0){   
            T top = top();   
            pop();   
            other.push(top);   
        }   
        StringBuffer buf = new StringBuffer();   
        while(other.count !=0){   
            buf.append(other.top());   
            other.pop();   
        }   
        return buf.toString();   
    }   
  
}