使用toString（）形成Java中的Object类

Question

导入java.util。*;

公共类MyStack {     私有ArrayList列表= new ArrayList <>（）;

public boolean isEmpty(){
    return list.isEmpty();
}
public int getSize(){
    return list.size();
}

public Object peek(){
    return list.get(getSize()-1);

}
public Object pop(){
    Object o = list.get(getSize() -1 );

    list.remove(getSize() -1);
    return o;
}

public void push(Object o ){
    list.add(o);
}

@Override
public String toString() {
    return "stack: " + list.toString();
}

public static void main(String[] args){
 MyStack mystack = new MyStack();
   mystack.push(mystack);
  System.out.println(mystack.isEmpty());
 System.out.println( mystack.getSize());
  System.out.println( mystack.peek());
  System.out.println(mystack.pop());

 System.out.println(mystack.toString());
}

}

问题是，当我运行这段代码时，由于toString（）方法，我得到了很多异常，而我不知道您能解决什么问题？

this is the stack trcae