Answered: The ADT stack lets you peek at its top…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

The ADT stack lets you peek at its top entry without removing it. For some applications of stacks, you
also need to peek at the entry beneath the top entry without removing it. We will call such an operation
peekNxt. If the stack has more than one entry, peekNxt returns the second entry from the top without altering the stack. If the stack has fewer than two entries, peekNxt throws an exception. Write a linked
implementation of a stack class call LinkedStack.java that includes a method peekNxt.

Implement p
import java.util.EmptyStackException;
import java.util.NoSuchElementException;
public final class LinkedStack<T> implements StackInterface<T>
{
private Node topNode;
public YourFirst_YourLast_LinkedStack()
{
topNode = null;
}
public void push(T newEntry)
{
Node newNode = new Node(newEntry, topNode);
topNode = newNode;
} // end push
public T peek()
{
if (isEmpty())
throw new EmptyStackException();
else
return topNode.getData();
} // end peek
public T peekNxt() // Code here
{

}
public T pop()
{
T top = peek();
topNode = topNode.getNextNode();
return top;
}
public boolean isEmpty()
{
return topNode == null;
}
public void clear()
{
topNode = null;
}
private class Node
{
private T data;
private Node next;
private Node(T dataPortion)

{
this(dataPortion, null);
}
private Node(T dataPortion, Node linkPortion)
{
data = dataPortion;
next = linkPortion;
}
private T getData()
{
return data;
} // end getData
private void setData(T newData)
{
data = newData;
}
private Node getNextNode()
{
return next;
}
private void setNextNode(Node nextNode)
{
next = nextNode;
}
}
}
--------------------------------------
public interface StackInterface<T>
{
/** Adds a new entry to the top of this stack.
@param newEntry An object to be added to the stack. */
public void push(T newEntry);

/** Removes and returns this stack's top entry.
@return The object at the top of the stack.
@throws EmptyStackException if the stack is empty before the operation. */
public T pop();

/** Retrieves this stack's top entry.
@return The object at the top of the stack.
@throws EmptyStackException if the stack is empty. */
public T peek();
/** Retrieves the entry just below this stack's top entry.
@return The object just below the top of the stack.
@throws EmptyStackException if the stack is empty.
@throws NoSuchElementException if the stack contains only one entry.
*/
public T peekNxt();
/** Detects whether this stack is empty.
@return True if the stack is empty. */
public boolean isEmpty();
/** Removes all entries from this stack. */
public void clear();
}

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