IntStack2.java

package chapter9;

//Another version of IntStack that has a private interface method that is used by two default methods.

public interface IntStack2 {
    void push(int item); //store an item

    int pop(); //retrieve an item

    //A default method that returns an array that contains the top n elements on the stack
    default int[] popNElements(int n) {
        //Return the requested elements.
        return getElements(n);
    }

    //A default method that returns an array that contains the next n elements on the stack after skipping elements
    default int[] skipAndPopNElements(int skip, int n) {

        //Skip the specified number of elements
        getElements(skip);

        //Return the requested elements
        return getElements(n);
    }

    //A private method that returns an array containing the top n elements on the stack
    private int[] getElements(int n) {
        int[] elements = new int[n];
        for (int i = 0; i < n; i++) elements[i] = pop();
        return elements;
    }

}