在java中执行堆栈操作以推送字符串,而不使用集合api

在我的java程序中,我想执行像push和pop这样的堆栈操作。我还想在堆栈操作中推字符串,但当我尝试推字符串时。我在截图中提到了错误。我应该如何更改push方法才能成功运行程序。

代码::

public class DataStack {

private static final int capacity = 3;  
 String arr[] = new String[capacity];  
 int top = -1;  

 public void push(String pushedElement) {  
  if (top < capacity - 1) {  
   top++;  
   arr[top] = pushedElement;    
   printElements();  
  } else {  
   System.out.println("Stack Overflow !");  
  }  
 }  

 public void pop() {  
  if (top >= 0) {  
   top--;  
   System.out.println("Pop operation done !");  
  } else {  
   System.out.println("Stack Underflow !");  
  }  
 }  

 public void printElements() {  
  if (top >= 0) {  
   System.out.print("Elements in stack : ");  
   for (int i = 0; i <= top; i++) {  
    System.out.println(arr[i]);  
   }  
  }  
 }  

 public static void main(String[] args) {  
  DataStack stackDemo = new DataStack();  

  stackDemo.push("china");  
  stackDemo.push("india"); 
  stackDemo.push("usa");    
 }
}

错误::