栈和队列

用数组实现栈，设置三个属性

1、maxSize 用来记录这个数组实现的栈能存放多少个数据
2、long[] stackArray 定义一个数组栈

3、top 记录栈顶

方法有

1、有参构造函数，创建一个栈，参数是栈的大小
2、push方法，压入一个数字

3、pop方法，弹出栈顶的一个数字

4、peek方法，查看栈顶的数字

5、isEmpty(),isFull()判断是不是空的栈和栈满了没有

/**
 * Description:用数组实现栈
 * @author 李弘昊2019年10月29日
 */
class StackX
{
    private int maxSize;        //size of stack array
    private long[] stackArray;
    private int top;            //top of stack

    public StackX(int s)        //constructor
    {
        maxSize = s;
        stackArray = new long[maxSize]; //create array
        top = -1;                //no items yet
    }

    public void push(long j)    //put item on top of stack
    {
        stackArray[++top] = j;    //increment top,insert item
    }

    public long pop()            //take item from top of stack
    {
        return stackArray[top--];//access items,decrement top
    }

    public long peek()            //peek at top of stack
    {
        return stackArray[top];
    }

    public boolean isEmpty()    //true if stack is empty
    {
        return(top == -1);
    }

    public boolean ifFull()        //true if stack is full
    {
        return(top == maxSize-1);
    }

}

public class StackApp
{
    public static void main(String[] args)
    {
        StackX theStack = new StackX(10);    //make new stack 

        theStack.push(20);                    //push items onto stack
        theStack.push(40);
        theStack.push(60);
        theStack.push(80);

        System.out.println("the top value:"+theStack.peek());

        while(!theStack.isEmpty())            //until it'empty
        {
            System.out.print(theStack.pop());
            System.out.print(" ");
        }
    }
}

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