在 Java 中创建带有数组的 Stack 类

Question

我正在尝试在 Java 中创建一个堆栈，该堆栈使用数组来实现。下面是我自定义的栈类中的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;
    }

当所有数据都从堆栈中弹出并且您尝试从中弹出一些内容时，应该抛出 EmptyStackException。但是， data.length 不会随着对象的弹出而改变。如果不能用 data.length 判断，pop 方法应该如何判断堆栈是否为空？

Answer 1

设置一个计数器来告诉您数组中的元素数量。 Array.length 单独会告诉您堆栈的容量，而不是堆栈中的元素数量。对于这个例子，count 是我的计数器

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;
}

还请注意，如果您正确实现堆栈，堆栈将自下而上增长，因此无需将所有元素移动到更靠近顶部的位置。所以如果你这样做，pop 方法应该是：

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

Answer 2

我建议你看看 Stack 类是如何实现的。它也使用一个数组，但是有一个 size 字段来保存堆栈的大小。

仅当大小增长大于数组长度时，数组才需要更改。

来自 Stack.pop();

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

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

    return obj;
}

顺便说一句，在堆栈中，您永远不需要重新排列元素。你应该从最后添加/删除。

在你的情况下，你可以写。

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

以下是用户定义的 Stack 代码如何在内部实现。

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;
    }
}

StackIntTest

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);
    }
}