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Welcome to Core Java Quiz. Java is an object-oriented programming language.
In this quiz, you will be tested on Core Java basics and OOPS concepts. There are some code snippets too to test your basic Java coding skills.
Some of the questions have multiple answers. You can click on the “Reveal Answer” button for the correct answer and explanation.
Give it a try and share it with others if you like it.
A. int myArray [] = {1, 3, 5};
B. int myArray [] [] = {1,2,3,4};
C. int [] myArray = (5, 4, 3);
D. int [] myArray = {“1”, “2”, “3”};
Correct Answer: A
int [] myArray = {“1”, “2”, “3”}; is invalid because String can’t be converted to an int.
int [] myArray = (5, 4, 3); is invalid because array elements should be defined in curly braces ({}).
int myArray [] [] = {1,2,3,4}; is invalid because myArray is a two-dimensional array whereas in this case it’s being defined as a one-dimensional array. The compiler will complain as Type mismatch: cannot convert from int to int[].
A. array
B. goto
C. null
D. int
**Correct Answer: B, D
**
The goto
and int
are reserved keywords in java. array
and null
are not keywords in java.
interface Foo{ int x = 10;}
public class Test {
public static void main(String[] args) {
Foo.x = 20;
System.out.println(Foo.x);
}
}
A. Prints 10
B. Prints 20
C. Compile Time Error
D. Runtime error because Foo.x is final.
**Correct Answer: C
**
By default, any field of the interface is public, static, and final. So we can’t change is, hence compile-time error at the statement Foo.x = 20;
.
public class Test {
public static void main(String[] args) {
char c = 65;
System.out.println("c = " + c);
}
}
A. Compile Time Error
B. Prints “c = A”
C. Runtime Error
D. Prints “c = 65”
**Correct Answer: B
**
Java compiler tries to automatically convert int to char. Since 65 gets converted to A, hence output will be “c = A”. The char values range is from u0000 to uffff. So char c = 65535;
is valid but char c = 65536;
will give compile time error.
public class Test {
public void main(String[] args) {
int x = 10*20-20;
System.out.println(x);
}
}
A. Runtime Error
B. Prints 180
C. Prints 0
D. Compile-time error.
Correct Answer: A
Runtime error because main method is not static. The error message will be Main method is not static in class Test, please define the main method as: public static void main(String[] args)
static
keyword in Java?A. We can have static block in a class.
B. The static block in a class is executed every time an object of class is created.
C. We can have static method implementations in interface.
D. We can define static block inside a method.
**Correct Answers: A, C
**
We can have static block in a class, it gets executed only once when class loads. From java 8 onwards, we can have static method implementations in interfaces.
A. Abstraction
B. Inheritance
C. Interface
D. Polymorphism
E. Generics
Correct Answers: A, B, D
OOPS core concepts are;
Read more at OOPS Concepts
A. The “extend” keyword is used to extend a class in java.
B. You can extend multiple classes in java.
C. Private members of the superclass are accessible to the subclass.
D. We can’t extend Final classes in java.
**Correct Answer: D
**
Inheritance is one of the core concepts in Java. You should be familiar with it. Please read the following articles to learn more about the answer choices - Inheritance in Java, Multiple Inheritance in Java.
package com.journaldev.java;
public class Test {
public static void main(String[] args) {
Super s = new Subclass();
s.foo();
}
}
class Super {
void foo() {
System.out.println("Super");
}
}
class Subclass extends Super {
static void foo() {
System.out.println("Subclass");
}
}
A. Compile time error
B. Super
C. Subclass
D. Runtime error
**Correct Answer: A
**
Subclass foo() method can’t be static, it will give compile time error This static method cannot hide the instance method from Super
.
package com.journaldev.java;
public class Test {
public static void main(String[] args) {
Subclass s1 = new Subclass();
s1.foo(); // line 6
Super s = new Subclass();
s.foo(); // line 8
}
}
class Super {
private void foo() {
System.out.println("Super");
}
}
class Subclass extends Super {
public void foo() {
System.out.println("Subclass");
}
}
A. Compile time error at line 6
B. Compile time error at line 8
C. Compile time error at both line 6 and 8
D. Works fine and prints “Subclass” two times.
**Correct Answer: B
**
Compile time error at line 8 because Super class foo() method is private. The error message is The method foo() from the type Super is not visible
.
import java.io.IOException;
public class Test {
public static void main(String[] args) {
try {
throw new IOException("Hello");
} catch (IOException | Exception e) {
System.out.println(e.getMessage());
}
}
}
A. Compile-time error
B. Prints “Hello”
C. Runtime Error
Correct Answer: A
Compile-time error as The exception IOException is already caught by the alternative Exception
.
public class Test {
public static void main(String[] args) {
String x = "abc";
String y = "abc";
x.concat(y);
System.out.print(x);
}
}
A. abcabc
B. abc
C. null
**Correct Answer: B
**
x.concat(y);
will create a new string but it’s not assigned to x, so the value of x is not changed.
A. RuntimeException
B. ClassCastException
C. NullPointerException
D. IOException
**Correct Answer: A, B, C
**
RuntimeException and its subclasses are unchecked exceptions. Unchecked exceptions do not need to be declared in a method or constructor’s throws clause.
package com.journaldev.java;
import java.io.IOException;
public class Test {
public static void main(String[] args) {
try {
throw new Exception("Hello ");
} catch (Exception e) {
System.out.print(e.getMessage());
} catch (IOException e) {
System.out.print(e.getMessage());
} finally {
System.out.println("World");
}
}
}
A. Compile-time error
B. Hello
C. Hello World
D. Hello Hello World
**Correct Answer: A
**
Compile-time error Unreachable catch block for IOException. It is already handled by the catch block for Exception
.
A. JVM is responsible for converting Byte code to the machine-specific code.
B. We only need JRE to run java programs.
C. JDK is required to compile java programs.
D. JRE doesn’t contain JVM
A. Yes
B. No
Correct Answer: A
This was a tricky question. We can have multiple methods having name as “main” in java through method overloading.
A. @interface keyword is used to create custom annotation
B. @Override is a built-in annotation in java
C. Annotations can’t be applied to fields in a class.
D. @Retention is one of the meta annotation in java.
E. Java annotation information gets lost when class is compiled.
**Correct Answer: A, B, D
**
For a complete explanation, read Java Annotations.
A. All java enum implicitly extends java.lang.Enum
class.
B. Java enum can implement interfaces.
C. We can create instance of enum using new operator.
D. Enums can’t be used in switch statements.
E. Enum constants are implicitly static and final.
**Correct Answer: A, B, E
**
Read more at Enum in Java.
A. Bootstrap Class Loader
B. Extensions Class Loader
C. Runtime Class Loader
D. System Class Loader
package com.journaldev.util;
public class Test {
public static String toString() {
System.out.println("Test toString called");
return "";
}
public static void main(String args[]) {
System.out.println(toString());
}
}
A. “Test toString called”
B. Compile-time error
C. “Test@7fh2bd8” (Object class toString() method is being called)
Correct Answer: B
We will get a compile-time error because we can’t have an Object class method overridden with the static keyword. The Object class has toString()
method. You will get a compile-time error as “This static method cannot hide the instance method from Object”.
public class Test {
public static void main(String[] args) {
String s1 = "abc";
String s2 = "abc";
System.out.println("s1 == s2 is:" + s1 == s2);
}
}
A. s1 == s2 is:true
B. false
C. s1 == s2 is:false
D. true
Correct Answer: B
The given statements output will be “false” because in java + operator precedence is more than == operator. So the given expression will be evaluated to “s1 == s2 is:abc” == “abc” i.e false.
I hope you liked the Core Java Quiz. If you think I have missed some important areas, let me know and I will add some more tricky quiz questions here.
Next Quiz: Java String Quiz
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Really Good Questions. Thanks sir…
- Himanshu Saxena
The last question was the final nail in the coffin. Extremely good questions sir ,Keep making more!!
- Rishabh Sharma
Really nice que’s. please update more tricky que’s
- Kokila Viswanathan
great work, thanks
- azin
LOL , at first question , answer is wrong The correct will be int[] array={1,2,3}; Not int array[] = {1,2,3};
- Dragos Todoroscean
The JRE includes the JVM, which is what actually interprets the byte code and runs your program. To do this the JVM uses libraries and other files provided by the JRE.
- joey
in question 4 i have copy your code and getting out is ‘c = A’ i have selected that option only but it says wrong option
- Achyut
Thanks for the quiz. 15th question blew my mind!
- Naseem Ahamed
I’m not sure what java version this was written against, but you most certainly can use Enums in switch statements. You couldn’t use strings in switch statements before Java 7, but even before that you could use Enums. Even the link in the description for why “Enums can’t be used in switch statements.” says that they can be used in switch statements.
- Nate
Java Runtime Environment (JRE) contains JVM, class libraries, and other supporting files.
- Tom