Important Notice:

Practice-It will be discontinued as of November 1st, 2024. After this date, the website will remain online for a transitional period, but login will be restricted to University of Washington NetID authentication. This marks the next phase towards the platform's full retirement. Thank you for your use and support of the application over the years.

If you are looking for an alternative, a similar tool, CodeStepByStep, was developed independently by the original author of Practice-It, and is available at codestepbystep.com**

logo Practice-It logo

Main Page → Problems → Solve a Problem

BJP4 Exercise 14.9: switchPairs

Language/Type: Java Collections Stacks and Queues
Author: Marty Stepp (on 2016/09/08)

Write a method switchPairs that takes a stack of integers as a parameter and that switches successive pairs of numbers starting at the bottom of the stack. For example, if the stack initially stores these values: 

bottom [3, 8, 17, 9, 99, 9, 17, 8, 3, 1, 2, 3, 4, 14] top

Your method should switch the first pair (3, 8), the second pair (17, 9), the third pair (99, 9), and so on, yielding this sequence: 

bottom [8, 3, 9, 17, 9, 99, 8, 17, 1, 3, 3, 2, 14, 4] top

If there are an odd number of values in the stack, the value at the top of the stack is not moved. For example, if the original stack had stored: 

bottom [3, 8, 17, 9, 99, 9, 17, 8, 3, 1, 2, 3, 4, 14, 42] top

It would again switch pairs of values, but the value at the top of the stack (42) would not be moved, yielding this sequence: 

bottom [8, 3, 9, 17, 9, 99, 8, 17, 1, 3, 3, 2, 14, 4, 42] top

Do not make assumptions about how many elements are in the stack. Use one queue as auxiliary storage.

Type your solution here:


This is a method problem. Write a Java method as described. Do not write a complete program or class; just the method(s) above.

You must log in before you can solve this problem.


Log In

If you do not understand how to solve a problem or why your solution doesn't work, please contact your TA or instructor.
If something seems wrong with the site (errors, slow performance, incorrect problems/tests, etc.), please

Is there a problem? Contact a site administrator.