未打印堆栈中输入的第一个节点(toString)

Question

首先，代码很长，但我只关心toString方法。我把所有东西都粘贴了，以防与之相关。

该代码应该检查输入的元素是否小于堆栈顶部的元素。我想好了那个部分。当我调用toString方法打印保存的输入时，它不会打印添加到堆栈中的第一个节点。但是，它会打印所有剩余的输入。例如，如果用户输入以下内容：

testing
test
te
t
What its currently outputing:
t te test
What it needs to output:
t te test testing

Main：

import java.util.*;
public class Stack {
public static void main(String args[]) {
    int loopInt = 1;
    PyramidStack<String> stringStack = new PyramidStack<String>();
    PyramidStack<Integer> intStack = new PyramidStack<Integer>();
    System.out
            .println("This program will save some of the strings you enter. ");
    System.out
            .println("Can you predict which ones will be saved?  (Enter nothing to quit.)");
    Scanner sc = new Scanner(System.in); // Opens Scanner for keyboard input
    try {
        do {
            System.out.print("Enter a String: ");
            String input = sc.nextLine();
            if (input.length() > 0) {
                if (stringStack.size() == 0) {
                    intStack.push(input.length());
                    stringStack.push(input);
                    System.out.println("String Saved");
                }
                else if (input.length() < intStack.peek()) {
                    stringStack.push(input);
                    intStack.push(input.length());
                    System.out.println("String Saved");
                }
                else {
                    System.out.println("String NOT saved. Already saved "
                            + intStack.countBefore(input.length())
                            + " strings that should come before this one.");
                }
            } else {
                System.out.println();
                System.out.println(stringStack.toString());
                System.out.println(intStack.toString());
                loopInt--;
                sc.close();
            }
        } while (loopInt > 0);
    } catch (NullPointerException e) {
        System.out.println("No strings have been entered. Ending the program.");
    }
}
}

金字塔堆叠法：

import java.util.*;
import java.lang.Comparable;
public class PyramidStack<E extends Comparable<E>> extends Stack<E> {
@Override
public void push(E item) throws IllegalArgumentException {
    if (super.size == 0) {
        super.push(item);
    }
    else if(item.compareTo(super.peek()) <= 0) {
        super.push(item);
    } 
    else {
        System.out.println("String NOT saved. " + countBefore(item) +  " strings that should come before this one.");
    }
}
@Override
public String toString() {
    Node<E> node;
    node = this.top;
    String s = "";
    while(node.getNext() != null){
        s += node.getData() + " ";
        node = node.getNext();
    }    
    return s;
}

public int countBefore(E item) {
    Node<E> node;
    node = this.top;
    int i = 0;
    while(node.getNext() != null){
        if(item.compareTo(super.peek()) <= 0) {
        node = node.getNext();
        }
        else{
        i++;
        node = node.getNext();
        }
    }
    return i;
}
}

Stack方法和Node方法。

Answer 1

while(node.getNext() != null){ s += node.getData() + " "; node = node.getNext(); }

这是您缺少的打印最后一个数据的地方。。您正在检查node.getnext（）为null。。所以它跳过最后一个对象，不打印。。您的状况应该是
node != null
或
循环结束后有此
s += node.getData()——由于节点不为null，因此不会出现null指针异常。。就像它检查node.getnext（）一样

希望它能帮助