Java Interview Questions and Answers for Freshers

Question 1

Which of these is NOT a primitive type in Java?

Accepted Answer

String. String is a class (an object type); the eight primitives are byte, short, int, long, float, double, char and boolean.

Question 2

What is the default value of an int field in a Java class?

Accepted Answer

0. Fields get default values: 0 for numbers, false for boolean, null for objects. Local variables have no default and must be initialised.

Question 3

Which keyword is used to inherit a class in Java?

Accepted Answer

extends. class B extends A. A class implements interfaces.

Question 4

How many classes can a Java class directly extend?

Accepted Answer

One. Java has single inheritance for classes; use interfaces for multiple types.

Question 5

What does JVM stand for?

Accepted Answer

Java Virtual Machine. The JVM runs compiled bytecode, which is why Java is 'write once, run anywhere'.

Question 6

Which method must every Java application have to start running?

Accepted Answer

public static void main(String[] args). The JVM looks for public static void main(String[] args).

Question 7

What is the difference between == and equals() for Strings?

Accepted Answer

== compares references, equals() compares contents. Two different String objects with the same text are equal() but not ==.

Question 8

Which collection does NOT allow duplicate elements?

Accepted Answer

HashSet. A Set keeps unique elements.

Question 9

What happens when you access index 5 of an array of length 5?

Accepted Answer

ArrayIndexOutOfBoundsException. Valid indexes are 0 to 4; Java checks bounds at run time.

Question 10

Which keyword prevents a method from being overridden?

Accepted Answer

final. A final method can't be overridden; a final class can't be extended.

Question 11

What is method overloading?

Accepted Answer

Same method name with different parameters in one class. Overloading is resolved at compile time; overriding happens in subclasses and is resolved at run time.

Question 12

Which of these is a checked exception?

Accepted Answer

IOException. Checked exceptions must be caught or declared with throws; the others are RuntimeExceptions.

Question 13

Can an interface have a method with a body in Java 8 and later?

Accepted Answer

Yes, default and static methods. Java 8 added default and static methods to interfaces.

Question 14

Why are Java Strings immutable?

Accepted Answer

For security, thread safety and the string pool. Immutable strings can be safely shared and cached in the string pool.

Question 15

Which class should you use to build a long string inside a loop?

Accepted Answer

StringBuilder. StringBuilder appends without creating a new object each time.

Question 16

What does the static keyword mean for a field?

Accepted Answer

One copy is shared by all objects of the class. Static members belong to the class, not to individual objects.

Question 17

Which access modifier makes a member visible only inside its own class?

Accepted Answer

private. private is the most restrictive; protected adds subclasses and the package.

Question 18

What is the time complexity of get(key) in a HashMap on average?

Accepted Answer

O(1). Hashing finds the bucket directly; worst case with many collisions is slower.

Question 19

What is garbage collection in Java?

Accepted Answer

Automatic freeing of objects that are no longer referenced. The JVM reclaims memory automatically; there is no delete in Java.

Question 20

Which keyword refers to the current object inside a method?

Accepted Answer

this. this.name = name; assigns the parameter to the field.

Question 21

What is the parent class of every class in Java?

Accepted Answer

Object. Every class extends java.lang.Object directly or indirectly.

Question 22

Which of these can NOT be instantiated with new?

Accepted Answer

An abstract class. Abstract classes exist to be extended; create objects of their concrete subclasses.

Question 23

What does this code print?
int a = 5, b = 2;
System.out.println(a / b);

Accepted Answer

2. Both operands are int, so / does integer division and drops the .5.

Question 24

What does this code print?
System.out.println("" + 10 + 20);

Accepted Answer

1020. The String comes first, so + joins text: "" + 10 + 20 = "1020".

Question 25

What does this code print?
System.out.println(10 + 20 + "Java");

Accepted Answer

30Java. Evaluated left to right: 10 + 20 = 30 first, then joined with "Java".

Question 26

What does this code print?
String a = "hi";
String b = new String("hi");
System.out.println((a == b) + " " + a.equals(b));

Accepted Answer

false true. new String creates a different object, so == is false; equals() compares the text.

Question 27

What does this code print?
int x = 5;
int y = x++;
System.out.println(y + " " + x);

Accepted Answer

5 6. x++ gives the old value (5) and then increments x to 6.

Question 28

What does this code print?
System.out.println("abc".charAt(1));

Accepted Answer

b. charAt counts from 0: index 1 is 'b'.

Question 29

What does this code print?
int[] a = {1, 2, 3};
System.out.println(a.length);

Accepted Answer

3. length is a field for arrays: {1, 2, 3} has 3 elements.

Question 30

What does this code print?
int n = 2;
switch (n) {
    case 1: System.out.print("One ");
    case 2: System.out.print("Two ");
    case 3: System.out.print("Three"); break;
    default: System.out.print("Default");
}

Accepted Answer

Two Three. There is no break after case 2, so execution falls through into case 3, which does break.

Question 31

What does this code print? java.util.List list = new java.util.ArrayList<>(java.util.List.of(1, 2, 3)); list.remove(1); System.out.println(list);

Accepted Answer

[1, 3]. remove(1) with an int removes the element at index 1 (the value 2).

Question 32

What does this code print?
class Parent { String name() { return "Parent"; } }
class Child extends Parent { String name() { return "Child"; } }
public class Main {
    public static void main(String[] args) {
        Parent p = new Child();
        System.out.println(p.name());
    }
}

Accepted Answer

Child. The object is a Child, so the overridden method runs (runtime polymorphism).

Question 33

What does this code print?
public class Main {
    static String f() {
        try { return "done"; }
        finally { System.out.print("finally "); }
    }
    public static void main(String[] args) {
        System.out.println(f());
    }
}

Accepted Answer

finally done. finally runs before the method returns, even when try has a return.

Question 34

What does this code print?
class Counter {
    static int count = 0;
    Counter() { count++; }
}
public class Main {
    public static void main(String[] args) {
        new Counter();
        new Counter();
        System.out.println(Counter.count);
    }
}

Accepted Answer

2. static count is shared by every Counter object, and two were created.

Question 35

What does this code print?
public class Main {
    static void change(int v) { v = 20; }
    public static void main(String[] args) {
        int x = 10;
        change(x);
        System.out.println(x);
    }
}

Accepted Answer

10. Java passes a copy of the int value; changing it inside the method doesn't affect x.

Question 36

What does this code print?
public class Main {
    static void change(int[] a) { a[0] = 99; }
    public static void main(String[] args) {
        int[] arr = {1, 2};
        change(arr);
        System.out.println(arr[0]);
    }
}

Accepted Answer

99. The array reference is copied, but it points to the same array, so the change is visible.

Question 37

What does this code print?
String s = "java";
String t = s.toUpperCase();
System.out.println(t + " " + s);

Accepted Answer

JAVA java. toUpperCase returns a new String; s itself never changes.

Question 38

What does this code print?
for (int i = 0; i < 3; i++) System.out.print(i + (i < 2 ? " " : ""));

Accepted Answer

0 1 2. The loop prints while i < 3: 0, 1, 2.

Question 39

What does this code print?
System.out.println(5.0 / 0);

Accepted Answer

Infinity. Dividing a double by zero gives Infinity; only integer division by zero throws.

Question 40

What does this code print? java.util.Map m = new java.util.TreeMap<>(); m.put("b", 2); m.put("a", 1); System.out.println(m);

Accepted Answer

{a=1, b=2}. A TreeMap keeps its keys sorted.

Question 41

What is the size of an int in Java?

Accepted Answer

32 bits. Java fixes primitive sizes on every platform; long is 64 bits.

Question 42

What is autoboxing?

Accepted Answer

Automatic conversion between a primitive and its wrapper class. int → Integer when adding to an ArrayList<Integer>.

Question 43

Which collection keeps keys in sorted order?

Accepted Answer

TreeMap. LinkedHashMap keeps insertion order; HashMap keeps no order.

Question 44

What is the difference between ArrayList and LinkedList?

Accepted Answer

ArrayList gives fast random access; LinkedList gives fast inserts/removes at the ends. ArrayList is backed by an array; LinkedList by doubly linked nodes.

Question 45

What does the transient keyword do?

Accepted Answer

Excludes a field from serialization. Used for passwords or derived values.

Question 46

What does the volatile keyword guarantee?

Accepted Answer

Reads and writes go to main memory so all threads see the latest value. It doesn't make compound operations like count++ atomic.

Question 47

What does the synchronized keyword do?

Accepted Answer

Lets only one thread run the block or method on the same lock at a time. Prevents race conditions.

Question 48

How do you create a thread in Java?

Accepted Answer

Extend Thread or implement Runnable (or use an ExecutorService). Call start(), not run(), to begin a new thread.

Question 49

What is the difference between Comparable and Comparator?

Accepted Answer

Comparable defines natural order inside the class; Comparator defines order outside it. compareTo(other) vs compare(a, b).

Question 50

What is the difference between throw and throws?

Accepted Answer

throw raises an exception; throws declares that a method may raise one. throw new IOException(); void read() throws IOException.

Question 51

What is a lambda expression in Java?

Accepted Answer

A short way to implement a functional interface. (a, b) -> a + b.

Question 52

What is a functional interface?

Accepted Answer

An interface with exactly one abstract method. Runnable, Comparator and Predicate are examples.

Question 53

What does Optional help avoid?

Accepted Answer

NullPointerException from missing values. Optional.ofNullable(x).orElse(default).

Question 54

What is the Stream API used for?

Accepted Answer

Processing collections with operations like filter, map and reduce. list.stream().filter(...).collect(...).

Question 55

What is the difference between JDK, JRE and JVM?

Accepted Answer

JDK has tools to develop; JRE has what's needed to run; JVM executes bytecode. JDK ⊃ JRE ⊃ JVM.

Question 56

What happens if hashCode() is not overridden along with equals()?

Accepted Answer

Equal objects may not be found in HashMap or HashSet. Equal objects must have equal hash codes.

Question 57

What is a static block?

Accepted Answer

Code that runs once when the class is loaded. static { ... } initialises static fields.

Question 58

What is method hiding?

Accepted Answer

A subclass static method with the same signature as a parent static method. Static methods are not overridden; they are hidden.

Question 59

Can we override a private method?

Accepted Answer

No, private methods aren't inherited. A subclass method with the same name is a new method.

Question 60

What is the purpose of the finalize() method?

Accepted Answer

It was called by the garbage collector before reclaiming an object (now deprecated). Use try-with-resources instead.

Question 61

What does try-with-resources do?

Accepted Answer

Closes resources like files automatically after the block. Resources must implement AutoCloseable.

Question 62

Which exception occurs when you call a method on a null reference?

Accepted Answer

NullPointerException. The most common Java runtime error.

Question 63

What is the default capacity growth of an ArrayList when full?

Accepted Answer

About 1.5 times. newCapacity = old + old / 2.

Question 64

What is a package in Java?

Accepted Answer

A namespace that groups related classes. e.g. java.util, java.io.

Java Interview Questions and Answers for Freshers

Q1. Which of these is NOT a primitive type in Java?

Q2. What is the default value of an int field in a Java class?

Q3. Which keyword is used to inherit a class in Java?

Q4. How many classes can a Java class directly extend?

Q5. What does JVM stand for?

Q6. Which method must every Java application have to start running?

Q7. What is the difference between == and equals() for Strings?

Q8. Which collection does NOT allow duplicate elements?

Q9. What happens when you access index 5 of an array of length 5?

Q10. Which keyword prevents a method from being overridden?

Q11. What is method overloading?

Q12. Which of these is a checked exception?

Q13. Can an interface have a method with a body in Java 8 and later?

Q14. Why are Java Strings immutable?

Q15. Which class should you use to build a long string inside a loop?

Q16. What does the static keyword mean for a field?

Q17. Which access modifier makes a member visible only inside its own class?

Q18. What is the time complexity of get(key) in a HashMap on average?

Q19. What is garbage collection in Java?

Q20. Which keyword refers to the current object inside a method?

Q21. What is the parent class of every class in Java?

Q22. Which of these can NOT be instantiated with new?

Q23. What does this code print?

Q24. What does this code print?

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Q26. What does this code print?

Q27. What does this code print?

Q28. What does this code print?

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Q40. What does this code print?

Q41. What is the size of an int in Java?

Q42. What is autoboxing?

Q43. Which collection keeps keys in sorted order?

Q44. What is the difference between ArrayList and LinkedList?

Q45. What does the transient keyword do?

Q46. What does the volatile keyword guarantee?

Q47. What does the synchronized keyword do?

Q48. How do you create a thread in Java?

Q49. What is the difference between Comparable and Comparator?

Q50. What is the difference between throw and throws?

Q51. What is a lambda expression in Java?

Q52. What is a functional interface?

Q53. What does Optional help avoid?

Q54. What is the Stream API used for?

Q55. What is the difference between JDK, JRE and JVM?

Q56. What happens if hashCode() is not overridden along with equals()?

Q57. What is a static block?

Q58. What is method hiding?

Q59. Can we override a private method?

Q60. What is the purpose of the finalize() method?

Q61. What does try-with-resources do?

Q62. Which exception occurs when you call a method on a null reference?

Q63. What is the default capacity growth of an ArrayList when full?

Q64. What is a package in Java?

Q65. What does the instanceof operator check?

Q66. Which is true about String literals in Java?

Q67. What is a marker interface?

Q68. What does the default keyword mean in an interface method?

Q69. What is the difference between HashMap and Hashtable?

Q70. What is the purpose of the super() call in a constructor?

Q71. What is an enum in Java?

Q72. What is the use of the break statement inside switch?

Q73. Which is the correct way to compare two Integer objects for value equality?

Q74. What is the result type of 'a' + 1 in Java?

Q75. Which keyword creates an object?

Q76. What is a wrapper class?

Q77. What is the purpose of the StringBuilder.reverse() method?

Q78. Which Java feature lets one method name work on many types, like List<T>?

Q79. What does this code print?