无法使用Java实现堆栈

Question

我无法理解为什么我的值没有存储在堆栈中。

UseStack.java

package test;
import java.util.Scanner;

class UseStack{
    private static Scanner obj;
    public static void main(String[] args) {
        obj = new Scanner(System.in);
        System.out.println("Enter the size of Stack....");
        int n = obj.nextInt();
        Stack stack = new Stack(n);
        while(true){
            System.out.println("1: Push");
            System.out.println("2: Pop");
            System.out.println("3: Show");
            int choice = obj.nextInt();;
            switch(choice){
                case 1:
                Push push = new Push(n);
                push.push();
                break;
                case 2:
                Pop pop = new Pop(n);
                pop.pop();
                break;
                case 3:
                Push push1 = new Push(n);
                push1.show();
                break;
                default:
                System.out.println("Invalid Option");
                break;
            }
        }
    }
}

Stack.java

package test;

    class Stack {
        public int arr[];
        public  int top;
        public  int capacity;
    
        public Stack(int size){
            this.arr = new int[size];
            capacity = size;
            top = -1;
        }
    }

Push.java

    package test;
    import java.util.Scanner;
    
    class Push extends Stack {
        public Push(int size) {
            super(size);
        }
    
        private static Scanner obj;
        public void push(){
obj = new Scanner(System.in);
            System.out.println("Enter Value to push...");
            int value = obj.nextInt();
            if(top==capacity-1){
                System.out.println("StackOverflow");
                return;
            }
            else{
                top++;
                arr[top]=value;
                System.out.println("Pushed...");
            }
        }



    public void show(){
        if(top==-1){
            System.out.println("StackUnderFlow");
            return;
        }
        else{
            System.out.println("Stack Elements : ");
            for(int i=top;i>=0;i--){
                System.out.println(arr[i]+" ");
            }
        }       
    }
}

Pop.java

package test;

class Pop extends Push{
    public Pop(int size) {
        super(size);
    }

    public void pop(){
        if(top==-1){
            System.out.println("StackUnderflow");
            return;
        }
        else{
            System.out.println("Poped.. "+arr[top]);
            top--;
        }
    }
}

请原谅我对发布整个代码的无知，在这个主题上已经问了几个问题，但是我应该做些什么来克服这个错误……

误差

当我在数组中推送两个值，然后试图显示元素时，我得到了堆栈流.

Answer 1

在Push.java中，您需要初始化obj扫描程序，例如

public void push(){
    obj = new Scanner(System.in);
    ...