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Interview Questions and Answers - Order By Rating

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 Q2941. Will this code compile fine ?

ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));		Core Java
Ans. Yes.

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   Like         Discuss         Correct / Improve     java   io   file   fileio   coding   code   objectoutputstream   fileoutputstream   yesno  file handling

 Q2942. What is the problem with this code ?

class BuggyBread1 {

private BuggyBread2 buggybread2;

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}		Core Java
Ans. Though we are trying to serialize BuggyBread1 object but we haven't declared the class to implement Serializable.

This will throw java.io.NotSerializableException upon execution.

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 Q2943. Will this code run fine if BuggyBread2 doesn't implement Serializable interface ?

class BuggyBread1 implements Serializable{
private BuggyBread2 buggybread2 = new BuggyBread2();

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}		Core Java
Ans. No, It will throw java.io.NotSerializableException.

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 Q2944. Will this code work fine if BuggyBread2 doesn't implement Serializable ?

class BuggyBread1 extends BuggyBread2 implements Serializable{
private int x = 5;

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}		Core Java
Ans. Yes.

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 Q2945. 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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 Q2946. Will this code Work ? If not , Why ?

java.util.Calendar c = new java.util.Calendar();		Core Java
Ans. No. It gives the error "Cannot Instantiate the type Calendar". Calendar is an abstract class and hence Calendar object should be instantiated using Calendar.getInstance().

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 Q2947. Is java.util.Date an abstract Class ? Is java.util.Calendar an abstract Class ?Core Java
Ans. Date is not a abstract class whereas Calendar is.

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 Q2948. What will the following code print ?

java.util.Calendar c = java.util.Calendar.getInstance();
c.add(Calendar.MONTH, 5);
System.out.println(c.getTime());		Core Java
Ans. Date and Time after 5 months from now.

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 Q2949. Which of the following code is correct ?

a. DateFormat df = DateFormat.getInstance();
b. DateFormat df = DateFormat.getDateInstance();
c. DateFormat df = DateFormat.getInstance(DateFormat.FULL);
d. DateFormat df = DateFormat.getDateInstance(DateFormat.FULL);		Core Java
Ans. All except c are correct.

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 Q2950. What is the use of parse method in DateFormat ?
Ans. It is used to parse String to get the Date Object with initialized date.

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 Q2951. Which of the following is not a valid java.util.Locale initialization ?

a. new Locale ()
b. new Locale ( String language )
c. new Locale ( String language , String country )		Core Java
Ans. a i.e new Locale()

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 Q2952. Which of the following is not a valid NumberFormat initialization ?

a. NumberFormat.getInstance()
b. NumberFormat.getDateInstance()
c. NumberFormat.getCurrencyInstance()
d. NumberFormat.getNumberInstance()		Core Java
Ans. b i.e NumberFormat.getDateInstance()

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 Q2953. What will the following code print ?

public static void main(String[] args){
Integer i1 = new Integer("1");
Integer i2 = new Integer("2");
Integer i3 = Integer.valueOf("3");
int i4 = i1 + i2 + i3;
System.out.println(i4);
}		Core Java
Ans. 6

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 Q2954. Which of the following syntax are correct ?a. LinkedList<Integer> l=new LinkedList<int>();b. List<Integer> l=new LinkedList<int>();c. LinkedList<Integer> l=new LinkedList<Integer>();d. List<Integer> l = new LinkedList<Integer>();Core Java
Ans. All are correct.

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   Like         Discuss         Correct / Improve     java   generics   linkedlist   list   collections      basic

 Q2955. Which of the following code is correct ?

a. Date date = DateFormat.newInstance(DateFormat.LONG, Locale.US).parse(str);

b. Date date = DateFormat.newInstance(DateFormat.LONG, Locale.US).format(str);

c. Date date = DateFormat.getDateInstance(DateFormat.LONG, Locale.US).parse(str);		Core Java
Ans. c

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 Q2956. 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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 Q2957. Which methods of the Pattern class have equivalent methods in the String class? Core Java
Ans. split() and macthes()

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 Q2958. Can we compare Integers by using equals() in Java ?Core Java
Ans. Yes for the Wrapper class Integer but not for the primitive int.

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 Q2959. What is comparator interface used for ?Core Java
Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.

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 Q2960. Which are the sorted collections ?Core Java
Ans. TreeSet and TreeMap

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   Like         Discuss         Correct / Improve     java   collections   treemap   treeset   basic interview question      basic        frequent

Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions.
  Q2961. What is rule regarding overriding equals and hashCode method ?Core Java
Ans. A Class must override the hashCode method if its overriding the equals method.

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 Q2962. What is the difference between Collection and Collections ?Core Java
Ans. Collection is an interface whereas Collections is a utility class.

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 Q2963. Is Java a statically typed or dynamically typed language ?
Ans. Statically typed

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  Q2964. What do you mean by "Java is a statically typed language" ?Core Java
Ans. It means that the type of variables are checked at compile time in Java.The main advantage here is that all kinds of checking can be done by the compiler and hence will reduce bugs.

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 Q2965. How can we reverse the order in the TreeMap ?
Ans. Using Collections.reverseOrder()

Map tree = new TreeMap(Collections.reverseOrder());

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 Q2966. TreeMap orders the elements on which field ?
Ans. Keys

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 Q2967. How TreeMap orders the elements if the Key is a String ?
Ans. As String implements Comparable, It refers to the String compareTo method to identify the order relationship among those elements.

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 Q2968. Can we add heterogeneous elements into TreeMap ?
Ans. No, Sorted collections don't allow addition of heterogeneous elements as they are not comparable.

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 Q2969. Will it create any problem if We add elements with key as user defined object into the TreeMap ?
Ans. It won't create any problem if the objects are comparable i.e we have that class implementing Comparable interface.

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  Q2970. Can we have null keys in TreeMap ?Core Java
Ans. No, results in exception.

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