堆棧添加機器不添加，但掛起等待更多的參數

Question

所以我有一個我建立的堆棧，我有一臺機器評估表達式，如（9 + 0），他們可以更復雜。我運行它有趣的命令行，然後當我鍵入示例（9 + 5）該程序就坐在那裏。我可以得到一個新行，但表達式不評估。所以我的問題是我錯過了什麼。我確信有些東西我沒有正確理解，並且我一直在想我缺少一些關於Scanner或Java中的數組的知識。

也許我昨天晚上在想，我應該用ArrayList替換數組。這有意義嗎？

這裏是固定容量堆疊

public class FCStack<Item> { 

private Item[] a; 
private int top; // pointer to top of Stack 
private int capacity; // size of the Stack+1 

public FCStack(int cap){ 
    capacity = cap; 
    a = (Item[]) new Object[capacity]; 
    top = 0; 
} 

public void push(Item i){ //will only push an Item to the Stack if there is room. 
    if (!isFull()) { 
     a[top++] = i; 
    } 
} 

public Item pop(){ //will only pop an Item from the stack if there is something to pop. 
    if (!isEmpty()) { 
     --top; 
    } 
    return a[top]; 
} 

public boolean isFull(){ //returns true if is full 
    return top == capacity; 
} 

public boolean isEmpty(){ //returns true if is empty 
    return top == 0; 
} 

public int size(){ //returns the current size of the stack+1 or the array index 
    return top; 
} 

}

下面是兩個堆棧評價

import java.io.*; 
import java.util.Scanner; 

public class TwoStackMaths { 

public static void main (String[] args) { 
    FCStack<String> ops = new FCStack<String>(10); 
    FCStack<Double> vals = new FCStack<Double>(10); 
    Scanner console = new Scanner(System.in); 
    while(console.hasNext()) { 
     String str = console.next(); 
     if (str.equals("(")) 
      ; 
     else if (str.equals("+")) { 
      ops.push(str); 
     } 
     else if (str.equals("-")) { 
      ops.push(str); 
     } 
     else if (str.equals("*")) { 
      ops.push(str); 
     } 
     else if (str.equals("/")) { 
      ops.push(str); 
     } 
     else if (str.equals("^")) { 
      ops.push(str); 
     } 
     else if (str.equals(")")) { 
      String op = ops.pop(); 
      double v = vals.pop(); 
      if (op.equals("+")) { 
       v = vals.pop() + v; 
      } 
      else if (op.equals("-")) { 
       v = vals.pop() - v; 
      } 
      else if (op.equals("*")) { 
       v = vals.pop() * v; 
      } 
      else if (op.equals("/")) { 
       v = vals.pop()/v; 
      } 
      else if (op.equals("^")) { 
       v = Math.pow(v, vals.pop()); 
      } 
      vals.push(v); 
     } 
     else { 
     vals.push(Double.parseDouble(str)); 
     } 
    } 
    //console.close(); 
    System.out.println(vals.pop()); 
} 

}

Answer 1

您的代碼爲我工作;我沒有改變它使用ArrayList，和我加了一個peek這樣

import java.util.ArrayList; 
import java.util.List; 
import java.util.Scanner; 

public class FCStack<T> { 

    public static void main(String[] args) { 
    FCStack<String> ops = new FCStack<String>(10); 
    FCStack<Double> vals = new FCStack<Double>(10); 
    Scanner console = new Scanner(System.in); 
    try { 
     while (console.hasNext()) { 
     String str = console.next().trim(); 
     if (str.equals(".")) { 
      System.out.println(vals.peek()); 
     } else if (str.equals("(")) { 
      ; 
     } else if (str.equals("+")) { 
      ops.push(str); 
     } else if (str.equals("-")) { 
      ops.push(str); 
     } else if (str.equals("*")) { 
      ops.push(str); 
     } else if (str.equals("/")) { 
      ops.push(str); 
     } else if (str.equals("^")) { 
      ops.push(str); 
     } else if (str.equals(")")) { 
      String op = ops.pop(); 
      double v = vals.pop(); 
      if (op.equals("+")) { 
      v = vals.pop() + v; 
      } else if (op.equals("-")) { 
      v = vals.pop() - v; 
      } else if (op.equals("*")) { 
      v = vals.pop() * v; 
      } else if (op.equals("/")) { 
      v = vals.pop()/v; 
      } else if (op.equals("^")) { 
      v = Math.pow(v, vals.pop()); 
      } 
      vals.push(v); 
     } else { 
      vals.push(Double.parseDouble(str)); 
     } 
    } 
    } finally { 
    console.close(); 
    } 
} 

private List<T> a; 
private int top; // pointer to top of FCStack 
private int capacity; // size of the FCStack+1 

public FCStack(int cap) { 
    capacity = cap; 

    a = new ArrayList<T>(); 
    top = 0; 
} 

public void push(T i) { // will only push an Item to 
         // the FCStack if there is room. 
    if (!isFull()) { 
    a.add(i); 
    ++top; 
    } 
} 

public T pop() { // will only pop an Item from the 
       // stack if there is something to pop. 
    if (!isEmpty()) { 
    return a.remove(--top); 
    } 
    return null; 
} 

public T peek() { 
    if (!isEmpty()) { 
    return a.get(top - 1); 
    } 
    return null; 
} 

public boolean isFull() { // returns true if is full 
    return top > capacity; 
} 

public boolean isEmpty() { // returns true if is empty 
    return top == 0; 
} 

    public int size() { // returns the current size of the 
         // stack+1 or the array index 
    return top; 
    } 
} 

測試，像這樣

(12.0 * 3.0) . 
36.0