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

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Q341. Which Java operator is right associative?

Core Java

Ans. The = operator is right associative.

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Q342. What is the difference between a break statement and a continue statement?

Core Java

Ans. Break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

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Q343. What is the purpose of the System class?

Core Java

Ans. The purpose of the System class is to provide access to system resources.

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Q344. Variable of the boolean type is automatically initialized as?

Core Java

Ans. The default value of the boolean type is false.

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Q345. Can try statements be nested?

Core Java

Ans. Yes

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Q346. What is the difference between the size and capacity of a Vector?

Core Java

Ans. The size is the number of elements actually stored in the vector, while capacity is the maximum number of elements it can store at a given instance of time.

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Q347. What is an enumeration?

Core Java

Ans. An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It allows sequential access to all the elements stored in the collection.

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Q348. In a case where there are no instance variables what does the default constructor initialize?

Core Java

Ans. Java expects the superclass ( Object Class ) constructor to be called while creation of any object. So super constructor is called in case there are no instance variables to initialize.

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Q349. How do you check memory leak in Java?

Core Java

Ans. You need to capture heap dump when it's in the healthy state. Start your application. Let it take real traffic for 10 minutes. At this point, capture heap dump. Heap Dump is basically the snapshot of your memory. It contains all objects that are residing in the memory, values stored in those objects, inbound

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Q350. Write a program to print the index of the first non repeated character in a java string

Core Java

Ans. public class BuggyBread1{
public static void main (String args[]) {
   String str = "hheello world";
   char[] charArray = str.toCharArray();
   char selectedChar = 'a';
   for(char char1: charArray){
      if(!str.contains(Character.toString(char1).concat(Character.toString(char1)))){
         selectedChar = char1;
         break;
      }
   }
   System.out.println(str.indexOf(Character.toString(selectedChar)));
}
}

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Q351. Which String class methods are used to make string upper case or lower case?

Core Java

Ans. toUpperCase and toLowerCase

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Q352. How to convert String to byte array and vice versa?

Core Java

Ans. We can use String getBytes() method to convert String to byte array and we can use String constructor new String(byte[] arr) to convert byte array to String.

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Q353. public class a {
   public static void main(String args[]){
      final String s1=""job"";
      final String s2=""seeker"";
      String s3=s1.concat(s2);
      String s4=""jobseeker"";
      System.out.println(s3==s4); // Output 1
      System.out.println(s3.hashCode()==s4.hashCode()); Output 2
   }
}

What will be the Output 1 and Output 2 ?

Core Java

Ans. S3 and S4 are pointing to different memory location and hence Output 1 will be false.

Hash code is generated to be used as hash key in some of the collections in Java and is calculated using string characters and its length. As they both are same string literals, and hence their hashcode is same.Output 2 will be true.

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Q354. What is the use of HashCode in objects ?

Core Java

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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Q355. Will finally be called always if all code has been kept in try block ?

Core Java

Ans. The only time finally won't be called is if you call System.exit() or if the JVM crashes first.

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Q356. Write a Program to add 1-100, 101-200, 201-300 in different threads and then sum the numbers ?

Core Java

Ans. public class TotalUsingThreads extends Thread{

   private static List<TotalUsingThreads> collector = new ArrayList<TotalUsingThreads>();

   private int startFrom = 0;

   private Integer threadTotal = null;

   Test(int startFrom){
      this.startFrom = startFrom;
   }


   public static void main(String[] args) throws InterruptedException{
      int totalSum = 0;

      // Create all the threads and set the count starting point for all of them
      for(int count=0;count<10;count++){
         TotalUsingThreads newThread = new TotalUsingThreads(count*100);
         newThread.start();
         collector.add(newThread);
      }

      boolean allCollected = false;


      // Make sure that all thread totals are collected and all threads have completed their tasks
      while(!allCollected){
         for(int count=0;count<10;count++){
            if(collector.get(count).threadTotal == null){
               Thread.sleep(100);
               break;
            }
         }
         allCollected = true;
      }

      // sum totals of all threads
      for(int count=0;count<10;count++){
         totalSum += collector.get(count).threadTotal;
      }

      System.out.println(totalSum);


   }

   public void run(){
      threadTotal = 0;
      for(int count=startFrom;count<startFrom+100;count++){
       threadTotal += count;
      }
   }
}

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Q357. If you have access to a function that returns a random integer from one to five, write another function which returns a random integer from one to seven.

Core Java

Ans. We can do that by pulling binary representation using 3 bits ( random(2) ).

getRandom7() {
   String binaryStr = String.valuesOf(random(2))+String.valuesOf(random(2))+String.valuesOf(random(2));
   binaryInt = Integer.valueOf(binaryStr);
   int sumValue=0;
   int multiple = 1;
   while(binaryInt > 0){
      binaryDigit = binaryInt%10;
      binaryInt = binaryInt /10;
      sumValue = sumValue + (binaryDigit * multiple);
      multiple = multiple * 2;
   }
}

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Q358. Write a method to convert binary to a number ?

Core Java

Ans.
convert(int binaryInt) {
   int sumValue=0;
   int multiple = 1;
   while(binaryInt > 0){
      binaryDigit = binaryInt%10;
      binaryInt = binaryInt /10;
      sumValue = sumValue + (binaryDigit * multiple);
      multiple = multiple * 2;
   }
   return sumValue;
}

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Q359. What will be the output of the following code ?

String s1 = "Buggy Bread";
String s2 = "Buggy Bread";
if(s1 == s2)
System.out.println("equal 1");
String n1 = new String("Buggy Bread");
String n2 = new String("Buggy Bread");
if(n1 == n2)
System.out.println("equal 2");

Core Java

Ans. equal 1

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Q360. what will be the output of this code ?

public static void main(String[] args){
   StringBuffer s1=new StringBuffer("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s.append("Bread");
}

Core Java

Ans. BuggyBread

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Q361. what will be the output of this code ?

public static void main(String[] args)    {
   String s1=new String("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s.append("Bread");
}

Core Java

Ans. Buggy

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Q362. what will be the output of this code ?

public static void main(String[] args)    {
   StringBuffer s1=new StringBuffer("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s=new StringBuffer("Bread");
}

Core Java

Ans. Buggy

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Q363. what will be the output ?

class Animal {
public void eat() throws Exception {
}
}

class Dog2 extends Animal {
public void eat(){}
public static void main(){
Animal an = new Dog2();
an.eat();
}
}

Core Java

Ans. Compile Time Error: Unhandled exception type Exception

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Q364. Can finally block throw an exception ?

Core Java

Ans. Yes. Methods invoked from within a finally block can throw an exception. Failure to catch and handle such exceptions results in the abrupt termination of the entire try block.

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Q365. What will the following code print when executed on Windows ?

public static void main(String[] args){
String parent = null;
File file = new File("/file.txt");
System.out.println(file.getPath());
System.out.println(file.getAbsolutePath());
try {
System.out.println(file.getCanonicalPath());
} catch (IOException e) {
e.printStackTrace();
}
}

Core Java

Ans. file.txtC:file.txtC:file.txt

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Q366. What will be the output of following code ?

public static void main(String[] args){
String child = null;
File file = new File("/folder", child);
try {
file.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}

Core Java

Ans. NullPointerException at line:File file = new File("/folder", child);

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Q367. What will be the output of following code, assuming that currently we are in c:Project ?

public static void main(String[] args){
String child = null;
File file = new File("../file.txt");
System.out.println(file.getPath());
System.out.println(file.getAbsolutePath());
try {
System.out.println(file.getCanonicalPath());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

Core Java

Ans. ..file.txt
C:WorkspaceProject..file.txt
C:Workspacefile.txt

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Q368. Which is the abstract parent class of FileWriter ?

Core Java

Ans. OutputStreamWriter

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Q369. Which class is used to read streams of characters from a file?

Core Java

Ans. FileReader

Sample Code for FileReader

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Q370. Which class is used to read streams of raw bytes from a file?

Core Java

Ans. FileInputStream

Sample Code for FileInputStream

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