的Java：堆栈 - > ArrayList的

Question

这是我到目前为止有：

System.out.println("\fStack - ArrayList Demo\n"); 

     ArrayList<String> al = new ArrayList<String>(); 
     Stack<String> st = new Stack<String>(); 

     // Start with a few elements to the ArrayList 
     al.add("A"); 
     al.add("B"); 
     al.add("C"); 

     st.addAll(al); // Retrieve ArrayList elements for the stack and add them there 
     al.clear(); // Clear arraylist for storage later 


     // Pop out the last element in the stack. 
     System.out.println("\nPop out the last element: "+al.add(st.pop())); 
     System.out.println("What's left of the stack: "+st+"\n"); 
     System.out.println("ArrayList, now: "+al); 

     // Keep popping.. 
     int count = st.search("A"); 
     while (count != -1 && count >= 1) { 
      System.out.println("Popping next.."+al.add(st.pop())); 
      count--; 
     } 

     // Is the Stack empty? 
     System.out.println("\nStack Empty? "+st.empty()); 
     System.out.println("ArrayList now: "+al); 

使用al.add(st.pop()));返回 “真”，当我运行程序。有没有办法让它产生被弹出的实际元素（A，B，C）？

Answer 1

的javadoc用于补充指出：

Returns: 
true (as specified by Collection.add(E)) 

这听起来像你想打印您要添加的元素。所以：

String elem = st.pop(); 
    System.out.println("adding " +elem); 
    al.add(elem) 

如果您打算成为一名软件开发人员，阅读和理解文档是一种宝贵的实践技能。