使用链表堆栈，使用后缀表达式读取输入文件答案

【问题标题】：Stack using linked list, reading input file with postfix expression使用链表堆栈，使用后缀表达式读取输入文件
【发布时间】：2018-04-27 01:45:32
【问题描述】：

我需要使用链表填充堆栈。我有一个名为 GenericStack 的通用类，带有常规方法。我有一个 Evaluator 类，它有我的主要方法，我必须读取后缀表达式的输入文件。我有一个 Node 类来构建链表。要使用 6 5 2 3 + 8 * + 3 + * 之类的后缀表达式读取文件，我不知道如何用文件填充链表或如何读取它。

 public class GenericStack {
        private Node top;
        public GenericStack(){
            top = null;
        }

        public boolean isEmpty(){
            return (top == null);
        }

        public void push (Object newItem){
            top = new Node(newItem,top);
        }

        public Objectpop(){
            if(isEmpty()){
                System.out.println("Trying to pop when stack is empty.");
                return null;
            }
            else{
                Node temp = top;
                top = top.next;
                return temp.info;
            }
        }

        void popAll(){
            top = null;
        }

        public Object peek(){
            if(isEmpty()){
                System.out.println("Trying to peek when stack is empty.");
                return null;
            }
            else{
                return top.info;
            }
        }
    }

    public class Evaluator {
        public static void main(String[] args){
            GenericStack myStack = new GenericStack();
        }
    }


public class Node {
    Object info;
    Node next;

    Node(Object info, Node next){
        this.info = info;
        this.next = next;
    }

}

【问题讨论】：

标签： java linked-list stack

【解决方案1】：

使用java.util.Scanner 逐行读取文件。然后自己实现evaluation()方法

import java.io.File;
import java.io.IOException;
import java.util.*;

public class Evaluator {

// Method that evaluates postfix expressions
private static int evaluate(String expression) {

    Stack<Character> stack = new Stack<>();

    // Implement evaluation algorithm here

    return 0;
}

public static void main(String[] args) throws IOException {

    // Path to file
    String path = "file.txt";

    // Reference to file
    File file = new File(path);

    // Scanner that scans the file
    Scanner scanner = new Scanner(file);

    // List that will contain lines from file
    List<String> list = new ArrayList<>();

    // Read file in memory, line by line
    while (scanner.hasNextLine()) {

        // Add each line to list
        list.add(scanner.nextLine());
    }

    int result;

    // Loop through each line in list
    for (String line : list) {

        // Evaluate postfix expression
        result = evaluate(line);

        // Display expression = result
        System.out.println(line + " " + result);
    }

}

}

【讨论】：