Hierarchical data with parent & child relationships are very common, and Java collection does not have a Tree data structure, hence it is a popular interview question. Further questions include tree data structure processing using recursiion & iteration. A Tree data structure can be represented as shown below.
Step 1: A simple Node.java class that encapsulates its value,
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Q1. How would you go about designing a “farm animals” application where animals like cow, pig, horse, etc move from a barn to pasture, a stable to paddock, etc? The solution should also cater for extension into other types of animals like circus animals, wild animals, etc in the future....
Q. Complete the method “changeDateFormat(String paragraph)” which takes a string input containing dates in mm/dd/yyyy format and converts them to “dd/mm/yyyy” format. For example, “My birthday is on 04/25/1980” becomes “My birthday is on 25/04/1980”
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public class Sentences { public static String changeDateFormat(String paragraph) { throw new RunTimeException("Complete this method."); // remove this line } public static void main(String[] args) { System.out.println(changeDateFormat("The season started on the 07/25/2015 and finished on the 08/09/2015, with a bang!!!.")); } } |
A.
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Q. Traverse the tree in depth and return a list of all passed nodes. It should handle different data types as Double, String, etc. The interface for the tree node is
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package tree; import java.util.List; public interface Node<E> { E getValue(); List<Node<E>> getChildren(); } |
A. Tree storing numbers: Tree storing text: #1. … Read more ›...
Auto-unboxing, switch, short circuit logical operators & exception handling are core Java basics that sometimes lead to obscure errors if not understood well & often tested in coding tests.
Q1. What is wrong with this code?
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public class WhatIsWrong { public static void main(String[] args) { double i = 2; switch (i) { case 1: System.out.println("First class"); break; case 2: System.out.println("Second class"); break; default: break; } } } |
A1. compile-error at switch(i) as switch works only with “int”
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Scenarios based Java OO concepts & GoF design patterns
Q. Complete the following “TreeProcessingImpl” class ….. so that the unit tests shown below pass? Skeleton Code
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package com.passing.unittests; import java.util.List; public interface Node<E> { E getValue(); List<Node<E>> getChildren(); } |
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package com.passing.unittests; import java.util.List; public class NodeImpl<E> implements Node<E> { private E value; private List<Node<E>> children; public NodeImpl(E value, List<Node<E>> children) { this.value = value; this.children = children; } public E getValue() { return value; } public List<Node<E>> getChildren() { return children; } } |
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package com.passing.unittests; public interface TreeProcessing<E> { abstract double getAverage(Node<E> node); abstract double getSum(Node<E> node); } |
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package com.passing.unittests; public class TreeProcessingImpl<E> implements TreeProcessing<Double> { public double getAverage(Node<Double> node) { return 0; } public double getSum(Node<Double> node) { return 0; } } |
Unit Tests
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package com.passing.unittests; import java.util.Arrays; import java.util.List; import org.junit.Assert; import org.junit.Before; import org.junit.Test; public class TreeProcessingTest { private TreeProcessing<Double> tp = null; private Node<Double> numberRootNode; @Before public void init() { tp = new TreeProcessingImpl<Double>(); Node<Double> lvl2a = new NodeImpl<Double>(6.0, null); Node<Double> lvl2b = new NodeImpl<Double>(7.0, null); Node<Double> lvl2c = new NodeImpl<Double>(8.0, null); @SuppressWarnings("unchecked") List<Node<Double>> lvl2Children = Arrays.asList(lvl2a, lvl2b, lvl2c); Node<Double> lvl1a = new NodeImpl<Double>(5.0, lvl2Children); Node<Double> lvl1b = new NodeImpl<Double>(9.0, null); @SuppressWarnings("unchecked") List<Node<Double>> lvl1Children = Arrays.asList(lvl1a, lvl1b); numberRootNode = new NodeImpl<Double>(7.0, lvl1Children); } @Test public void testGetAverage() { Assert.assertEquals("Wrong", (6.0+7.0+8.0+5.0+9.0+7.0)/6, tp.getAverage(numberRootNode), 0.01); } @Test public void testSum() { Assert.assertEquals("Wrong", (6.0+7.0+8.0+5.0+9.0+7.0), tp.getSum(numberRootNode), 0.01); } } |
A. … Read more ›...
Q. Complete the method “canAttendAll(Collection seminars)” which takes a collection of seminar objects with start and end timestamps, and the method should determine if there is an overlap in seminars events. In other words, if you can attend all the seminars.
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import java.text.SimpleDateFormat; import java.util.ArrayList; import java.util.Collection; import java.util.Date; public class SeminarWeek { public static Boolean canAttendAll(Collection<Seminar> seminars) { return false; } public static void main(String[] args) throws Exception { SimpleDateFormat sdf = new SimpleDateFormat("y-M-d H:m"); ArrayList<Seminar> seminars = new ArrayList<Seminar>(); seminars.add(new Seminar(sdf.parse("2015-01-13 09:00"), sdf .parse("2015-01-13 16:30"))); seminars.add(new Seminar(sdf.parse("2015-01-12 09:30"), sdf .parse("2015-01-12 17:00"))); seminars.add(new Seminar(sdf.parse("2015-01-14 09:10"), sdf .parse("2015-01-14 16:30"))); System.out.println(SeminarWeek.canAttendAll(seminars)); } } class Seminar { private Date start, end; public Seminar(Date start, Date end) { this.start = start; this.end = end; } public Date getStart() { return this.start; } public Date getEnd() { return this.end; } } |
The above code needs to be saved into...
The following post improves on the design flaws listed in the previous post entitled 02: Scenarios based Java OO design & GoF design patterns – naive Template Method pattern. Scenario: A company named XYZ Retail is in the business of selling Books, … Read more ›...
Q. Complete the method “isValidBST(Node root)” which takes a “Tree node” as an input to evaluate if the input is a valid BST (i.e. Binary Search Tree)?
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public class BinarySearchTree { public static boolean isValidBST(Node root) { throw new RuntimeException("To be completed"); } public static void main(String[] args) { Node n4 = new Node(2, null, null); Node n5 = new Node(4, null, null); Node n6 = new Node(6, null, null); Node n7 = new Node(8, null, null); Node n1 = new Node(3, n4, n5); Node n3 = new Node(7, n6, n7); //root node Node n2 = new Node(5, n1, n3); System.out.println(isValidBST(n2)); } } class Node { public int value; public Node left, right; public Node(int value, Node left, Node right) { this.value = value; this.left = left; this.right = right; } } |
A. Detailed answers on recursive & … Read more ›...
Q1. What are the different binary tree traversal mechanisms? A1. Traversing a tree means visiting all the nodes of a tree in order. Many different binary tree algorithms involve traversals. For example, if you wish to count the number of employees in an organizational chart you must visit each node....
Q1. Have you seen job advertisements requiring Java candidates to work in real-time or high volume transaction processing systems? A1. If you are applying for such jobs, you can be quizzed on Big O notation. Here are some basics to brush up on. … Read more ›...
Q6. What is wring with this code?
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public class WhatIsWrong { public static void main(String args[]) { float sum = 0; while (sum != 1.0) { sum += 0.1; } System.out.print("The sum is: "+sum); } } |
A6. Infinite loop at due to sum != 1.0. Using floating point variables like float or double in loops to compare for equality can lead to infinite loops. Comparing for “” or “
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