在 Java 中使用數組創建 Stack 類

Question

我正在嘗試在 Java 中創建一個使用數組進行實現的堆棧。 下面是我自定義的堆棧類中的pop()方法

public E pop()
    {
        if(data.length == 0)
        {
            throw new EmptyStackException();
        }
        E poppedObject = data[0];
        for(int i = 0; i < data.length-1; i++) //Moving all the elements one closer to top
        {
            data[i] = data[i+1];
        }
        return poppedObject;
    }

當所有數據都已從堆棧中彈出並嘗試從中彈出某些內容時，應拋出 EmptyStackException。 然而，data.length 不會隨着對象的彈出而改變。 如果無法通過 data.length 判斷，pop 方法如何判斷堆棧是否為空？

Answer 1

設置一個計數器來告訴您數組中元素的數量。 Array.length 單獨會告訴您堆棧的容量，而不是堆棧中元素的數量。 在這個例子中， count是我的計數器

public E pop() throws EmptyStackException {
    if(count <= 0) {
        throw new EmptyStackException();
    }
    E poppedObject = data[0];
    for(int i = 0; i < count; i++) { //Moving all the elements one closer to top
        data[i] = data[i+1];
    }
    count--;
    return poppedObject;
}

另請注意，如果您正確實現堆棧，堆棧將自下而上增長，因此不需要將所有元素移近頂部。 所以如果你這樣做的話， pop方法應該是：

public E pop() throws EmptyStackException {
    if(count == 0) {
        throw new EmptyStackException();
    } 
    return data[--count];
}

Answer 2

我建議你看看 Stack 類是如何實現的。 它也使用一個數組，但有一個大小字段，用於保存大小的堆棧。

僅當大小增長大於數組長度時，才需要更改數組。

從 Stack.pop();

public synchronized E pop() {
    E       obj;
    int     len = size();

    obj = peek();
    removeElementAt(len - 1);

    return obj;
}

順便說一句，在堆棧中，您永遠不需要重新排列元素。 您應該從最后添加/刪除。

在你的情況下，你可以寫。

public int size() { return size; }

public void push(E e) {
    if (size == data.length) growArray();
    data[size++] = e;
}

public E pop() {
    if (size == 0) throw new EmptyStackException();
    return data[--size];
}

Answer 3

下面是用戶定義的堆棧代碼如何在內部實現。

class UserDefinedStack< E> {

    private static int defaultCapacity = 5;
    private E[] stack = null;
    int top = -1;

    /**
     * The default constructor will create stack of type with default size 5
     *
     */
    UserDefinedStack() {
        stack = (E[]) new Object[defaultCapacity];

    }

    /**
     * constructs a stack with initial size
     *
     * @param defaultSize is the size of the stack
     */
    UserDefinedStack(int defaultCapacity) {
        this.defaultCapacity = defaultCapacity;
        stack = (E[]) new Object[defaultCapacity];
    }

    public void push(E element) {
        top = top + 1;
        if (defaultCapacity == top) {
            //System.err.println("Stack is Full!...");
            // System.out.println("re-creating new resizable Array!..");
            stack = constructsResizableArray(stack, defaultCapacity);
            //throw new RuntimeException("Statck Full!...");
        }
        stack[top] = element;

    }

    /**
     * This method will remove the top of the element and return
     *
     * @return <tt>E</tt> returns top of the element
     *
     */
    public E pop() {

        if (top == -1) {
            System.out.println("Stack is Empty!...");
            throw new RuntimeException("Statck Empty!...");
        }
        E e = stack[top];
        stack[top] = null;
        top--;
        return e;
    }

    /**
     * This method will return top of the element and without remove
     *
     * @param <E> the type of element to insert
     * @return <tt>E</tt> returns top of the element
     *
     */
    public E peek() {

        if (top == -1) {
            System.out.println("Stack is Empty!...");
            throw new RuntimeException("Statck Empty!...");
        }
        E e = stack[top];
        return e;
    }

    public E[] constructsResizableArray(E[] stack, int defaultCapacity) {
        UserDefinedStack.defaultCapacity = defaultCapacity * 2;
        E[] newstack = (E[]) new Object[UserDefinedStack.defaultCapacity];
        int i = 0;
        for (E e : stack) {
            newstack[i] = e;
            i++;
        }
        stack = null;
        //System.out.println("New Array returned back");
        return newstack;
    }

    /**
     * Iterate the stack over the elements
     *
     */
    public void iterateStack() {
        for (E e : stack) {
            System.out.print("::" + e);
        }
    }

    public long size() {
        return top + 1;
    }

    public long capacity() {
        return this.stack.length;
    }
}

堆棧信息測試

import java.util.ArrayList;
import java.util.Date;
import java.util.Stack;

/**
 *
 * @author rajasekhar.burepalli
 */
public class StackIntTest {

    public static void main(String[] args) {
        System.out.println("Using Customized Stack!...............");
        Date startDate = new Date();
        System.out.println("StartTime:::" + startDate);
        UserDefinedStack< Integer> is = new UserDefinedStack<>();
        for (int i = 1; i < 1212121; i++) {
            is.push(i);
        }
        System.out.println("Size::::::" + is.size() + "---Capacity:::" + is.capacity());
        System.out.println("end Time::" + new Date());

        System.out.println("Using java.util.Stack!...............");

        System.out.println("StartTime:::" + startDate);
        Stack< Integer> is1 = new Stack<>();
        for (int i = 1; i < 1212121; i++) {
            is1.push(i);
        }
        System.out.println("end Time::" + new Date());
        System.out.println("Size::::::" + is1.size() + "---Capacity:::" + is1.capacity());

        System.out.println("Using java.util.ArrayList!...............");
        System.out.println("StartTime:::" + startDate);
        ArrayList< Integer> al = new ArrayList<>();
        for (int i = 1; i < 1212121; i++) {
            al.add(i);
        }
        System.out.println("end Time::" + new Date());
        System.out.println("Size::::::" + al.size());

    }
}

Answer 4

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    //CREATING A STACK USING ARRAYS
    
    //EXAMPLE
    //CREATE AN ARRAY
    int[] numbers = new int[5];
    
    //Create a variable to find out the current elements position
    int pointer = 0 ; 
    
    //Add elements to the array
    for (int i = 0 ; i < numbers.length ; i++){
        numbers[pointer++] = input.nextInt();
    }
    
    //Last In first Out
    //Create a variable to store the removed element
    int temp;
    for (int i = 0; i < numbers.length; i++) {
        pointer -= 1;
        temp = numbers[pointer];
        numbers[pointer] = 0 ;
        
        System.out.println(temp);
    }
}