Interview Questions and Answers for 'Java' | Search Interview Question

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Q271. Do you think that Java should have had pointers ?

Core Java

Ans. Open ended Questions.

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Q272. Tell something about history of Java ?

Core Java

Ans. Java was initially found in 1991 by James Gosling, Sun Micro Systems. At first it was called as "Oak". In 1995 then it was later renamed to "Java". java is a originally a platform independent language. Currently Oracle, America owns Java.

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Q273. How to find if JVM is 32 or 64 bit from Java program. ?

Core Java

Ans. You can find JVM - 32 bit or 64 bit by using System.getProperty() from Java program.

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Q274. According to Java Operator precedence, which operator is considered to be with highest precedence?

Core Java

Ans. Postfix operators i.e () [] . is at the highest precedence.

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Q275. What is Comparable Interface?

Core Java

Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.

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Q276. What is Externalizable interface?

Core Java

Ans. Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism.

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Q277. What are the features of encapsulation ?

Core Java

Ans. Combine the data of our application and its manipulation at one place.

Encapsulation Allow the state of an object to be accessed and modified through behaviors.

Reduce the coupling of modules and increase the cohesion inside them.

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Q278. Write a method to check if input String is Palindrome?

Core Java

Ans. private static boolean isPalindrome(String str) {

if (str == null)
return false;

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

return strBuilder.toString().equals(str);

}

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Q279. Write a method that will remove given character from the String?

Core Java

Ans.

private static String removeChar(String str, char c) {    

   if (str == null)        

      return null;     

   

   return str.replaceAll(Character.toString(c), "");

}

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Q280. Why String is popular HashMap key in Java?

Core Java

Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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Q281. What does String intern() method do?

Core Java

Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

Moreover provide reference for scp object for corresponding string object present in heap memory.

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Q282. Will the following program display ""Buggy Bread"" ?

class Test{
   static void display(){
      System.out.println(""Buggy Bread"");
   }
}

class Demo{
   public static void main(String... args){
      Test t = null;
      t.display();
   }
}

Core Java

Ans. Yes. static method is not accessed by the instance of class. Either you call it by the class name or the reference.

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Q283. How substring() method of String class create memory leaks?

Core Java

Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string.

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Q284. Write a program to reverse a string iteratively and recursively ?

Core Java

Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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Q285. Write a Program to check if 2 strings are Anagrams ?

Core Java

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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Q286. Difference between new operator and Class.forName().newInstance() ?

Ans. new operator is used to statically create an instance of object. newInstance() is used to create an object dynamically ( like if the class name needs to be picked from configuration file ). If you know what class needs to be initialized , new is the optimized way of instantiating Class.

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Q287. Difference between ArrayList and LinkedList ?

Ans. LinkedList and ArrayList are two different implementations of the List interface. LinkedList implements it with a doubly-linked list. ArrayList implements it with a dynamically resizing array.

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Q288. What are the pre-requisite for the collection to perform Binary Search ?

Ans. 1. Collection should have an index for random access.
2. Collection should have ordered elements.

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Q289. Which of the following syntax is correct ?import static java.lang.System.*;or static import java.lang.System.*;

Core Java

Ans. import static java.lang.System.*;

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Q290. What will be the output of following Code ?

class BuggyBread {
   public static void main(String[] args) {
      String s2 = "I am unique!";
      String s5 = "I am unique!";

      System.out.println(s2 == s5);
   }
}

Core Java

Ans. true, due to String Pool, both will point to a same String object.

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Q291. What will be the output of following code ?
class BuggyBread2 {
   private static int counter = 0;
   void BuggyBread2() {
      counter = 5;
   }

   BuggyBread2(int x){
      counter = x;
   }

   public static void main(String[] args) {
      BuggyBread2 bg = new BuggyBread2();
      System.out.println(counter);
   }
}

Core Java

Ans. Compile time error as it won't find the constructor matching BuggyBread2().
Compiler won't provide default no argument constructor as programmer has already defined one constructor.
Compiler will treat user defined BuggyBread2() as a method, as return type ( void ) has been specified for that.

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Q292. Can we add duplicate keys in a HashMap ? What will happen if we attempt to add duplicate values ?

Ans. No, We cannot have duplicate keys in HashMap. If we attempt to do so , the previous value for the key is overwritten.

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Q293. What are different types of cookies ?

Java EE

Ans. Session cookies , which are deleted once the session is over.

Permanent cookies , which stays at client PC even if the session is disconnected.

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Q294. Can we have try and catch blocks within finally ?

Core Java

Ans. Yes, if we have a cleanup code that might throw an exception in the finally block, then we can have a try-catch block

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Q295. Will this code compile fine ?

ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));

Core Java

Ans. Yes.

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Q296. Can we compose the Parent Class object like this ?

class BuggyBread1 extends BuggyBread2 {

private BuggyBread2 buggybread2;

public static void main(String[] args){
buggybread2 = new BuggyBread2();
}
}

Ans. Yes.

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Q297. What's wrong with this code ?

public static void main(String[] args) {
String regex = "(\\w+)*";
String s = "Java is a programming language.";

Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(s);
while (matcher.next()) {
System.out.println("The e-mail id is: " + matcher.group());
}
}

Core Java

Ans. matcher.find() should have been used instead of matcher.next() within while.

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Q298. Which are the sorted collections ?

Core Java

Ans. TreeSet and TreeMap

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Q299. What is the difference between these two approaches of creating singleton Class ?

//Double Checked Locking Code
public static Singleton createInstance() {
   if(singleton == null){
      synchronized(Singleton.class) {
         if(singleton == null) {
            singleton = new Singleton();
         }
      }
   }
   return singleton;
}

//Single checked locking code
public static Singleton createInstance() {
   synchronized(Singleton.class) {
      if(singleton == null) {
         singleton = new Singleton();
      }
   }
   return singleton;
}

Design

Ans. In First Case , Lock for the synchronized block will be received only if singleton == null whereas in second case every thread will acquire the lock before executing the code.
The problem of synchronization with singleton will only happen when the object has not be instantiated. Once instantiated , the check singleton == null will always generate true and the same object will be returned and hence no problem. First condition will make sure that synchronized access ( acquiring locks ) will only take place if the object has not been created so far.

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Q300. Does java allow implementation of multiple interfaces having Default methods with Same name and Signature ?

Core Java

Ans. No. Compilation error.

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