Part 11
Interview questions on Collections in java for experienced covered in this post:
What is Properties Class? What is the role of properties class?
- Properties class is used to read the values from multiple
sources like config file, properties file etc.
- The main advantage of this approach is if there is a change
in the properties file to reflect that change in java class then just
re-deployment is required, Not required to rebuild the project.
- In our project, if any changes are required frequently like
username, password, the port number is not recommended to hardcode in the
java program, If there is any change to reflect that change requires
recompilation, rebuild and redeployment. Even sometimes server restart may
require which may impact the business.
- To overcome this problem we can set values in the properties
file and then just redeploy is required if any change is there.
- Please refer to the below examples.
1. In the first example, we are reading values from the
properties file.
2. In the second example, we are setting values to the
properties file.
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1 First example we are reading values from properties file. package simplifiedjava.crackedInterview;
import
java.io.FileInputStream;
import
java.util.Enumeration; import java.util.Properties; public class PropertiesFileDemo {
public static void
main(String[] args){ Properties properties = new Properties();
try {
FileInputStream fis = new
FileInputStream("G:\\Core
Java\\InterviewPrograms\\src\\javaproperties.properties");
properties.load(fis);
} catch
(Exception e) {
System.out.println("File Not Found");
e.printStackTrace(); }
Enumeration enumeration = properties.propertyNames();
while(enumeration.hasMoreElements()) {
String propName
= (String)enumeration.nextElement();
String value = properties.getProperty(propName);
System.out.println(propName + " Value is = " + value);
}
}
}
Output:
port Value is = 8080
password Value is = yogi@12345 username Value is = yogi 2. Second example we are setting values to properties file. package simplifiedjava.crackedInterview;
import
java.io.FileOutputStream;
import
java.io.IOException; import java.util.Properties; public class PropertiesFileDemo {
public static void
main(String[] args){ Properties properties = new Properties();
try {
FileOutputStream fos = new
FileOutputStream("G:\\Core
Java\\InterviewPrograms\\src\\javaproperties.properties");
properties.setProperty("url", "thin:driver:oracle:4848");
properties.store(fos, "URL added");
} catch
(IOException e) {
e.printStackTrace();
}
}
}
Output:
javaproperties.properties:
#URL added
#Mon Nov 01 14:08:17 IST 2021
url=thin\:driver\:oracle\:4848 |
 
Note: Please click on Image to Purchase the books from Amazon.in |
What is Dictionary class?
- A java Dictionary is an abstract class that stores elements
in the form of key-value pairs.
- The Dictionary class is the abstract parent of any class,
such as Hashtable, which maps keys to values.
- Every key and every value is an object.
- In any one Dictionary object, every key is associated with at
most one value.
- Any non-null object can be used as a key and as a value.
- Please refer to the below example.
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package simplifiedjava.crackedInterview;
import
java.util.Dictionary; import java.util.Hashtable; public class DictionaryClassDemo {
public static void
main(String[] args) {
Dictionary<Integer, String> dictionary = new
Hashtable<Integer, String>();
dictionary.put(10, "Ten");
dictionary.put(100, "Hundred");
dictionary.put(1000, "Thousand");
dictionary.put(1, "One");
System.out.println(dictionary);
}
}
Output: {1000=Thousand, 10=Ten, 1=One, 100=Hundred}
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Why map doesn't extends Collection interface?
- Map doesn’t extend the Collection interface because they are
not compatible.
- Internal data structure of Collection implementations are
like a list of objects and the internal data structure of the map is
key-value pair.
- Collection implementations are index-based collections.
- Map is not an indexed based collection but it is key-value
based collection.
- For adding objects to the collection we use add(Object o)
method.
- For adding objects to the map we use the put(key, value)
method.
- In the case of iterator, we directly put the iterator on the
collection implementation class.
- But, In the case map, we have to put the iterator on the
entry set.
Can you write a code to iterate a hashMap object?
- We can iterate Hashmap couple of ways.
1. The first way is we can collect keyset and iterate the map
and print the vales.
2. The second way is we can collect the entry set and iterate
map and print the values.
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package simplifiedjava.crackedInterview;
import
java.util.HashMap;
import
java.util.Iterator; import java.util.Map; public class HashMapIteratorDemo {
public static void
main(String[] args) {
HashMap<Integer, String> hMap = new
HashMap<Integer, String>();
hMap.put(1, "One");
hMap.put(10, "Ten");
hMap.put(100, "Hundred"); hMap.put(1000, "Thousand"); System.out.println("=============== Using KeySet===============");
Iterator itr1 = hMap.keySet().iterator();
while(itr1.hasNext()) {
Integer key
= (Integer) itr1.next();
System.out.println("Key : "+ key + "\t Value : "+ hMap.get(key));
}
System.out.println("=============== Using EntrySet===============");
Iterator itr2 = hMap.entrySet().iterator();
while(itr2.hasNext()) {
Map.Entry<Integer, String> pair
= (Map.Entry<Integer, String>)itr2.next();
System.out.println("Key : " + pair.getKey()+ "\tValue : "+ pair.getValue());
}
}
}
Output:
=============== Using KeySet===============
Key : 1 Value : One
Key : 100 Value : Hundred
Key : 1000 Value : Thousand
Key : 10 Value : Ten
=============== Using EntrySet===============
Key : 1 Value : One
Key : 100 Value : Hundred
Key : 1000 Value : Thousand
Key : 10 Value : Ten |
Which data structure has implemented for HashMap?
- Hashtable data structure has been implemented for
HashMap.
Which data structure has implemented for TreeMap?
- RED-BLACK Tree data structure has been implemented for
TreeMap.
Can I convert Map into List?
- We can convert the map into a List.
- But we have to create a different list for the key set and
value set.
- Please refer to the below example.
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package simplifiedjava.crackedInterview;
import
java.util.ArrayList;
import
java.util.HashMap; import java.util.List; public class ConvertMapToList {
public static void
main(String[] args) {
HashMap<Integer, String> hMap = new
HashMap<Integer, String>();
hMap.put(1, "One");
hMap.put(10, "Ten");
hMap.put(100, "Hundred"); hMap.put(1000, "Thousand");
List<Integer> keyList = new
ArrayList<Integer>(hMap.keySet()); List<String> valueList = new ArrayList<String>(hMap.values());
System.out.println("Key List "+ keyList);
System.out.println("Value List "+ valueList);
}
}
Output:
Key List [1, 100, 1000, 10]
Value List [One, Hundred, Thousand, Ten]
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What is hash-collision in Hashtable and how will you handled in Collection API?
- Two different keys with the same hash value are known as
hash-collision.
- Two separate entries will be kept in a single hash bucket to
avoid the collision.
- There are two ways to avoid hash-collision. Separate Chaining
and Open Addressing.
1.
Separate Chaining:
§ Keys are stored inside and outside the hashtable.
§ Extra space is required for the pointers to store the keys
outside the hashtable.
§ Some buckets of the hash table are never used which leads to
wastage of space.
§ Cache performance is poor. This is because of linked lists
which store the keys outside the hash table.
2.
Open Addressing:
§ All the keys are stored inside only in the hash table. No key
is present outside the Hashtable.
§ No extra space is required.
§ Buckets may be used even if non-mapped keys to those
particular buckets.
§ Cache performance is better. This is because there is no
linked lists are used.
-
Java interview questions and answers all MNC - Click here
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Basic core java interview questions and answers for freshers
- Click here
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Core java interview questions for 3 years experience - Click here
-
Core java interview questions and answers for 3-5 years exp
- Click here
-
Core java interview questions and Answers for 5 - 7 Years exp
- Click here
-
Basic Java Interview Questions and Answers - Click here
-
Java interview questions and answers on oops - Click here
-
Java interview questions and answers on Strings - Click here
-
Java interview questions on exception handling - Click here
-
Interview questions on multithreading in java for experienced
- Click here
-
Interview questions on serialization in java for experienced
- Click here
-
Interview questions on inner class in java for experienced
- Click here
-
Interview questions on Collections in java for experienced
- Click here
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Thank you techies for visiting this blog. I hope you enjoyed this blog and got more technical knowledge. I have tried to cover all types of questions and provided examples tested on eclipse as much as I can. Guys, please don’t just mug up the questions and answers. Try to clear your concepts with examples. Try to write a code on eclipse once you read the concepts. It will help you to memorize the concepts for a very long time. Simultaneously you will be prepared for interview programs as well. It will help you to survive in the IT sector for a long time. It may be easy to crack an interview but it's really tough to survive in the IT industry with inadequate knowledge and skills. I have collected all the questions from actual interviews attended by my friends, colleagues, college mate and classmate. I have covered frequently asked questions as well as challenging questions. I have included many programs to understand the concept thoroughly. I will try to explain the concept with the help of a real-time program in eclipse. You can share more questions which are not covered in this blog or post. Always welcome your suggestions and queries. I will definitely try to resolve it. Please comment your queries and new set of questions under the comment sections. I will create a new post for those questions.
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I had worked with many multi-national companies like
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Softwares. Fortunately, TCS and Cybage has
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