在过去的几个小时里，我一直在试图弄清楚如何获取数组列表的值，但我似乎找不到任何真正有用的东西来回答我的问题。我正在尝试得到这个结果:
STACK TESTING
4
8
8
9
The size of the stack is: 3
The stack contains:
9
7
3
现在我可以进行堆栈测试，然后是 4、8、8、9，但是我无法获取堆栈的实际大小以打印它包含的项目数，然后打印其中的每个单独项目像上面的列表。每当我尝试在 toString 方法中使用某些内容时，它都会给我一个类似于“无法在数组类型 T[] 上调用 size() 的错误。如果我使用 stack.length 其输出 100 但这不是我需要的。我” m 主要处理 isEmpty()、size() 和 toString()
这是我的代码:
import java.util.Arrays;
public class Murray_A05Q1 {
public static void main(String[] args) {
ArrayStack<Integer> stack = new ArrayStack<Integer>();
System.out.println("STACK TESTING");
stack.push(3); // <----- bottom
stack.push(7);
stack.push(4); // <----- top
System.out.println(stack.peek()); // <--- peeking top so 4
stack.pop(); // <----- popping off top so its popping off 4
stack.push(9);
stack.push(8); // <---- new final top 8,9,7,3
System.out.println(stack.peek()); // <------ peeking at 8
System.out.println(stack.pop()); // <------ popping off 8 to leave 9,7,3
System.out.println(stack.peek()); // <------ peeking now at 9
int value = stack.size();
System.out.println("The size of the stack is: " + stack.size());
System.out.println("The stack contains:\n" + stack.toString());
} // End of main method header
public static class ArrayStack<T> implements StackADT<T>
{
private final static int DEFAULT_CAPACITY = 100;
private int top;
private T[] stack;
/**
* Creates an empty stack using the default capacity.
*/
public ArrayStack()
{
this(DEFAULT_CAPACITY);
}
/**
* Creates an empty stack using the specified capacity.
* @param initialCapacity the initial size of the array
*/
@SuppressWarnings("unchecked") //see p505.
public ArrayStack(int initialCapacity)
{
top = 0;
stack = (T[])(new Object[initialCapacity]);
}
/**
* Adds the specified element to the top of this stack, expanding
* the capacity of the array if necessary.
* @param element generic element to be pushed onto stack
*/
public void push(T element)
{
if (size() == stack.length)
expandCapacity();
stack[top] = element;
top++;
}
/**
* Creates a new array to store the contents of this stack with
* twice the capacity of the old one.
*/
private void expandCapacity()
{
stack = Arrays.copyOf(stack, stack.length * 2);
}
/**
* Removes the element at the top of this stack and returns a
* reference to it.
* @return element removed from top of stack
* @throws EmptyCollectionException if stack is empty
*/
public T pop() throws EmptyCollectionException
{
if (isEmpty())
throw new EmptyCollectionException("stack");
top--;
T result = stack[top];
stack[top] = null;
return result;
}
/**
* Returns a reference to the element at the top of this stack.
* The element is not removed from the stack.
* @return element on top of stack
* @throws EmptyCollectionException if stack is empty
*/
public T peek() throws EmptyCollectionException
{
if (isEmpty())
throw new EmptyCollectionException("stack");
return stack[top-1];
}
/**
* Returns true if this stack is empty and false otherwise.
* @return true if this stack is empty
*/
//*****************************
// First one to be implemented
//*****************************
public boolean isEmpty()
{
return (stack == null);
}
/**
* Returns the number of elements in this stack.
* @param stack2
* @return the number of elements in the stack
*/
public int size()
{
return 0; // have this set to 0 temporary since I'm getting the error
}
/**
* Returns a string representation of this stack. The string has the
* form of each element printed on its own line, with the top most
* element displayed first, and the bottom most element displayed last.
* If the list is empty, returns the word "empty".
* @return a string representation of the stack
*/
public String toString()
{
return stack.size;
}
}
}
为此，我还有三个附加文件:
文件#1
public class LinearNode<T>
{
private LinearNode<T> next;
private T element;
/**
* Creates an empty node.
*/
public LinearNode()
{
next = null;
element = null;
}
/**
* Creates a node storing the specified element.
* @param elem element to be stored
*/
public LinearNode(T elem)
{
next = null;
element = elem;
}
/**
* Returns the node that follows this one.
* @return reference to next node
*/
public LinearNode<T> getNext()
{
return next;
}
/**
* Sets the node that follows this one.
* @param node node to follow this one
*/
public void setNext(LinearNode<T> node)
{
next = node;
}
/**
* Returns the element stored in this node.
* @return element stored at the node
*/
public T getElement()
{
return element;
}
/**
* Sets the element stored in this node.
* @param elem element to be stored at this node
*/
public void setElement(T elem)
{
element = elem;
}
}
文件#2
public interface StackADT<T>
{
/**
* Adds the specified element to the top of this stack.
* @param element element to be pushed onto the stack
*/
public void push(T element);
/**
* Removes and returns the top element from this stack.
* @return the element removed from the stack
*/
public T pop();
/**
* Returns without removing the top element of this stack.
* @return the element on top of the stack
*/
public T peek();
/**
* Returns true if this stack contains no elements.
* @return true if the stack is empty
*/
public boolean isEmpty();
/**
* Returns the number of elements in this stack.
* @return the number of elements in the stack
*/
public int size();
/**
* Returns a string representation of this stack.
* @return a string representation of the stack
*/
public String toString();
}
最后，文件#3
public class EmptyCollectionException extends RuntimeException {
/**
* Sets up this exception with an appropriate message.
* @param collection the name of the collection
*/
public EmptyCollectionException(String collection)
{
super("The " + collection + " is empty.");
}
}
谁能向我解释一下，为什么我无法在 toString()、size() 和 isEmpty() 方法中执行任何操作，而不会出现指向 T[] 的错误？
非常感谢!!
最佳答案
你可能想要这样的东西
public boolean isEmpty()
{
return (top == 0);
}
/**
* Returns the number of elements in this stack.
* @param stack2
* @return the number of elements in the stack
*/
public int size()
{
return top; // have this set to 0 temporary since I'm getting the error
}
/**
* Returns a string representation of this stack. The string has the
* form of each element printed on its own line, with the top most
* element displayed first, and the bottom most element displayed last.
* If the list is empty, returns the word "empty".
* @return a string representation of the stack
*/
public String toString()
{
int top1 = top -1;
String finishedString = "";
for(int i = top1;i >= 0;i--)
{
finishedString += stack[i].toString() + "\n";
}
return finishedString;
}
关于java - 在 Java 中实现 ArrayList 并获取各个值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31735664/