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Q241. If everything is an object , Cant we declare every object as

Object obj = new String();

Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc.

We cannot access methods defined in String class or in any class in hierarchy between String and Object.

For example - we cannot do obj.append("abc") as it will now give compile time error.

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Q242. Which type of memory is cleaned / recovered by garbage collection - stack or heap ?

Ans. Heap memory.

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Q243. Write a program to print all even numbers first and then all odd numbers till 100. For example the output should be
2
4
6
8
...... 100
and then
1
3
5
7
...... 99

using only 1 for loop ? Is it possible with just one loop ?

Ans. Yes , It can be done using single for loop

public class BuggyBread{
public static void main (String args[]) {
   int x = 50;
   for(int i=1;i <= 100;i++){
      if(i<=50){
         System.out.println(i*2);
      } else {
         System.out.println(i-x);
         x = x - 1;
      }
   }
}
}

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Q244. Given two files with list of words, write a program to show the common words in both files

Ans. import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.io.*;
public class Common {
public static void main(String ar[])throws Exception
   {
      File f=new File("a.txt");
File f1=new File("x.java");
      System.out.println(f.exists());
FileInputStream fin = new FileInputStream(f);
      FileInputStream fin1 = new FileInputStream(f1);

      byte b[]=new byte[10000];
byte b1[]=new byte[10000];
fin.read(b);
fin1.read(b1);
String s1 = new String(b);
String s2 =new String(b1);

String words1[] = s1.trim().split(" ");
String words2[] = s2.trim().split(" ");
Listlist1 = new ArrayList<>(Arrays.asList(words1));
Listlist2 = new ArrayList<>(Arrays.asList(words2));
list1.retainAll(list2);
System.out.println(list1);
}
}

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Q245. What is the difference between for and foreach loop in java ? Which one should be used in which cases ?

Ans. 1. for loop in java is used with a counter as following

for(int counter=0;counter < 50;counter++){
System.out.println(list.get(counter));
}

for iterating and printing the contents of a collection

whereas foreach loop can be specified directly without the use of counter

for(String str:list){
System.out.println(list.get(counter));
}

2. for Each loop syntax is more clean if we have to iterate over the elements of a collection and we need not keep track of the record count

3. For is preferred when we need loops without the usage of collections or Array of objects and entirely primitives are being used

4. for loop is preferred if we need to keep track of record count and have to perform some action of the basis of that. For example - If we have to print something after every 5 records, With for each loop in such case, we will have to keep a separate counter.

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Q246. Does java supports operator overloading ?

Ans. No

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Q247. When is the situation when finally section won't execute ?

Ans. If the process / app is abruptly killed or terminated.

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Q248. What is the use of static keyword in Java ?

Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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Q249. Is it a good practice to use Asterick(*) in import statement to load multiple packages with single import statement ?

Ans. No, we should be lean in loading only packages which are required. Loading packages which are not being used result in memory overheads.

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Q250. Can we override wait() or notify() methods?

Ans. wait and notify are declared final in object class and hence cannot be overridden.

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Q251. Write a multi threaded Program that will simulate transferring of money across accounts ?

^{This question was recently asked at 'Trustwave'.This question is still unanswered. Can you please provide an answer.}

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Q252. Write a Program to print factorial of a number using recursion

Ans. public class BuggyBread {
public static void main(String args[]) {
System.out.println(factorial(5));
}

private static int factorial(int number){
if(number == 1){
return 1;
} else {
return number * factorial(number - 1);
}
}
}

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Q253. What access the variable gets if we don't provide any access specifier ?

Ans. It gets the default access i.e package protected.

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Q254. How Marker interfaces works internally ?

^{This question was recently asked at 'GGK Technologies'.This question is still unanswered. Can you please provide an answer.}

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Q255. Can we overload abstract methods ?

Ans. Yes

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Q256. What are the advantages of using methods in Java ?

Ans. Likewise classes, methods also provide a way for code reuse and abstraction. Code is reused, clean and easy to understand if classified properly within classes and methods.

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Q257. Why can't we create an instance of abstract class ? Why is it restricted by compiler ?

Ans. Because Abstract class is incomplete i.e there are abstract methods that needs to be defined by extending classes.

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Q258. Why do we need polymorphism in Java ?

Ans. Frankly saying I dont see much use of method overloading as its just little design convenience as you can use the same name but still have binding to different methods depending on the need.

Method overriding is really important and is much more useful than method overloading. Along with other programming concepts like interfaces and dependency injection , it facilitates the development of software as libraries and plug-gable components.

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Q259. What is the difference between a keyword and a modifier ?

Ans. Keywords are the reserved words that have a pre defined meaning for a compiler whereas modifiers are the type of keywords that modifies the state or definition of a programming construct.

for, while are keywords but not modifiers.
private , public , final , abstract etc are keywords as well as modifiers.

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Q260. What is the difference between keywords, identifiers and literals in java ?

Ans. Keywords are the reserved words that have a pre defined meaning for the compiler and hence are restricted to be used as identifiers.

Identifiers are the name assigned to different programming constructs like classes, interfaces, methods , variables etc.

Literals are the values that are assigned to Identifiers.

For example

int count = 0;

in the above statement "int" is a keyword, "count" is an identifier and "0" is a literal

Sample Code for keywords

Sample Code for identifiers

Sample Code for literals

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Q261. How does java identifies which method to be called in method overriding or runtime polymorphism, when both methods share the same name and signature ?

Ans. Java identifies the method to be called at runtime by the object that is being referenced.

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Q262. What is the difference between following two segments of code

Code 1

int x = 4 * 3;
int y = x * 5;

Code 2

int y = 4 * 3 * 5;

Ans. Both will produce the same output but 1st will consume more resources in terms of memory ( for maintaining intermediate value ) and computing power ( as single mathematical calculation with more operands is more effective than multiple calculations with broken down operands )

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Q263. Java doesn't provide exclusive access to memory like C/C++ and other lower level languages ? What are the advantanges and disadvantages ?

Ans. Yes, doesn't provide exclusive access as we cannot allocate and deallocate memory exclusively as Java internally manages it. The advantage of this is that it relieves the coder for such tasks and helps protect from many bugs that may get introduced with imperfect coding. Moreover as java garbage collector collects all unclaimed memory or objects, it helps the application from memory leaks.

On the flip side , as coder doesn't have extensive excess to memory , it is upto java to decide on the state for programming construct and data storage and hence may introduce some security risks. For example - Java keeps string literals in string pool and there is no exclusive way to remove it and hence may stay and sensitive data in string pool may introduce security issues. Moreover when we overwrite a value or object for a variable / reference, it is upto java to purge those values and hence it may stay in memory for a while till java decide that it is no longer referenced and hence should be removed and hence makes it vulnerable for inappropriate access.

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Q264. Is it ok to use optional everywhere just to get over nullpointerexception ?

Ans. Optional is to be used for arguments / atrributes which are indeed optional i.e the request should continue even if they aren't provided. It should not be used for mandatory attributes or arguments as we would like application to shout out ( with error message / exception trace ) to signify a problem.

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Q265. Do you prefer using var args ?

Ans. Though var args are used rarely but they are pretty useful if a method is expected to receive variable number of arguments. For example - it's pretty useful for the main method as the caller has the flexibility to provide arguments in infinite ways.It provides a convenience and flexibility to the caller.

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Q266. What is meant by "Vector is synchronized and ArrayList isn't " ?

Ans. It means that only 1 thread can access have access to Vector at a time and no parallel access is allowed whereas Array List allows parallel access by multiple threads.

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Q267. Can a class be declared "protected" ?

Ans. No, only methods can be declared protected.

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Q268. Is String final in Java ?

Ans. Strings are immutable in Java and not final.

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Q269. What are ascii values for capital and lower case alphabets ?

Ans. 65 to 90 for capital case alphabets

97 to 122 for lower case alphabets

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Q270. How can we ensure thread safety in static method ?

Ans. By using synchronized static method or synchronized block

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