堆栈添加机未添加，但挂起等待更多的参数

您的代码对我有用；我确实将其更改为使用ArrayList，并添加了一个

peek

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 FCStackprivate int capacity; // size of the FCStack+1public 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;  }}

像这样测试

( 12.0 * 3.0 ) .36.0