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Q391. what is fail fast and Fail Safe in collections?

Ans. Iterators in java are used to iterate over the Collection objects.

Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element.

Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection.

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Frequently asked in Genpact.

Q392. What is object cloning ?

Ans. Its is the process of creating exact copy of an object being cloned. In Object class one native method called clone() is there which is meant for Shallow Cloning of Object. Shallow cloning means bitwise copy of an object.In case of primitive data type it will create an exact copy of primitive values as well as variables but if the object contains any reference of an object then it will not copy the referenced object rather it will create the copy of reference variable and assigned it to the old object.

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Q393. Explain OOps concepts.

Ans. There are four main OOP concepts in Java. These are:

Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times.

Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide.

Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel.

Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below.

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Q394. how does abstraction help your application ?

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Q395. Difference between Class Path and Build Path ?

Ans. The build path is used for building your application. It contains all of your source files and all Java libraries that are required to compile the application.

The classpath is used for executing the application. This includes all java classes and libraries that are needed to run the java application.

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Q396. Difference between JVM, JRE and JDK ?

Ans. JDK(Java Development kit) = Development Kit comprising of JVM , library and development tools for developers

JRE (Java Run time Environment) - Comprise of JVM and set of libraries

JVM(Java Virtual Machine) = Interpreter which reads the .class file line by line.

When we install JDK, JRE also get installed so we can write,compile and excute our code. Used by developer. Without JDK we can only execute the program using JRE.

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Q397. Which objects are eligible for garbage collection ?

Ans. Objects that have lost their reference i.e. they cannot be accessed/used by the program anymore.

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Q398. How can i split a linked list in two parts in java 8?

Ans. This can be done using a Spliterator.

LinkedList list = Arrays.asList("names","numbs","birds","animals");
Spliterator split1 = list.Spliterator();
Spliterator split2 = split1.Spliterator();

Now, the LinkedList is split into split1 and split2.
use split2 first then split1 to check the output.

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Q399. What is the default data type of Serialized methods?'

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Q400. Why cant we start an identifier with a number in Java?

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Q401. Which java features makes java different from other languages ?

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Q402. What is mutable in Java ?

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Q403. what are different pointer operators used ?

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Q404. Write a method it will return reverse of the string(with out using reverse method of String or StringBuffer)

Ans. String s1 = "akhilesh";
char[] ch = s1.toCharArray();
for (int i = ch.length-1 ; i >=0 ; i--) {
System.out.print(ch[i]);
}

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Q405. What is the default data type of state variables in Clonable interface and Serializable interface ?

Ans. Cloneable and Serializable are Marker Interfaces, So these are empty interfaces with no variables.

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Q406. Write a method that takes an integer and verifies if the number is power of 10.

Ans. public static boolean isPowerOfTen(long input) {

if (input % 10 != 0 || input == 0) {
return false;
}

if (input == 10) {
return true;
}

return isPowerOfTen(input/10);
}

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Q407. A Kid can go up 1, 2 or 3 stairs in one step. Write a method that takes number of steps in a stair will print all possible ways he can take.

For example , printAllCombinations(3) should print

111
12
21
3

Similarly , printAllCombinations(4) should print

1111
121
13
211
22
31
4

Ans. public static String findStep(int n) {
if (n == 1 || n == 0)
return 1;
else if (n == 2)
return 2;
else
return findStep(n - 3) + findStep(n - 2) + findStep(n - 1);
}

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Q408. What is a double ended queue?

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Q409. Can we override wait() or notify() ?

Ans. No, because these are final.

public final void wait() throws InterruptedException

public final void notify()

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Q410. How much by default filling ratio in HashMap ?

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Q411. How to convert array to list in Java ?

Ans. We can use Arrays.asList

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Q412. Suppose we have a string "Java is object oriented language" and we have to reverse every alternate word in string. How would we do that using Java program.

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Q413. What are annotations and what are it's advantages ?

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Q414. How ConcurrentHashMap provides better performance compared to HashTable ?

Ans. ConcurrentHashMap uses multiple buckets to store Data and hence avoid read locks which facilitates better performance.

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Q415. What is the use of Object class ?

Ans. 1. Default definition for some of the methods , like equals, hashcode etc that gets carried to all objects even if you don't define anything. But that default definition is kind of like assigning 0 to integer, it just provide a safe state , nothing much for comparison.

2. Places where you have no idea about what object you may receive and just want to perform out of 8 basic methods of object class, something like printing their string representation ( defined by their toString method ), or equality ( using their equals method )

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Q416. How is LinkedList collection class internally implemented ? Is it a Linked List or Doubly Linked List ?

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Q417. What are the benefits of immutability or Immutable classes ?

Ans. Immutable objects are thread-safe so you will not have any synchronization issues.Immutable objects are good for Map keys and Set elements, since these typically do not change once created.Immutability makes it easier to write, use and reason about the code (class invariant is established once and then unchanged)Immutability makes it easier to parallelize your program as there are no conflicts among objects.The internal state of your program will be consistent even if you have exceptions.References to immutable objects can be cached as they are not going to change.

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Q418. Which immutable classes have you worked with ? Can you name some immutable Collections ? How to make an immutable collection ?

Ans. string and wrapper class objects

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Q419. What is a BlockingQueue ?

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Q420. Do we have sorted collection for List ?

Ans. Not in java.util

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