stack method in Java

* create
```
import java.util.*;
  
class Main {   
    public static void main (String[] args) {
        Stack<Integer> s = new Stack<>();
    }
}
```
* iterator: Java stack has iterator, but it is a bad design. A stack that can be iterated is no different from a plain vector.
* add
```
import java.util.*;
  
class Main {   
    public static void main (String[] args) {
        Stack<Integer> s = new Stack<>();
        s.push(1);
        System.out.println(s);
    }
}
```
* change (N/A)
* query
```
import java.util.*;
  
class Main {   
    public static void main (String[] args) {
        Stack<Integer> s = new Stack<>();
        s.push(1);
        System.out.println(s.peek());
        System.out.println(s.empty());
        System.out.println(s.size());
    }
}
```
* delete 
```
import java.util.*;
  
class Main {   
    public static void main (String[] args) {
        Stack<Integer> s = new Stack<>();
        s.push(1);
        System.out.println(s.peek());
        s.pop();
        System.out.println(s.empty());
        System.out.println(s.size());
    }
}
```
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