Top 30 Java Basic Interview Questions for Freshers

Java Basic Interview Questions for Freshers

Following are some java basic interview questions

Q 1: What is the most Important feature of java?

Ans: Java is platform independent language.

Q 2: What do you mean by Platform Independence?

Ans: Platform Independence  you can run and compile program in one platform and can execute in any other platform.

Q 3: What is JVM?

Ans: The Java interpreter along with the runtime environment required to run the Java application in called as Java virtual machine(JVM)

Q 4: What is the difference between a JDK and a JVM?

Ans: JDK is Java Development Kit which is for development purpose and it includes execution environment also. But JVM is purely a run time environment and hence you will not be able to compile your source files using a JVM.

Q 5: What is the base class of all classes?

Ans: java.lang.Object

Q 6: What is JIT Compiler?

Ans: Just-In-Time(JIT) compiler is  used to improve the performance. JIT compiles parts of the byte code that have similar functionality at the same time,

Q 7: Are JVM’s Platform Independent?

Ans: JVM’S are not platform Independent. JVM’S are platform Specific.

Q 8: What is are packages?

Ans: A package is a collection of related classes and interfaces providing access protection and namespace management.

Q 9: What if main method declare as private?

Ans: No,It will compile fine but in run time it will error like main method should be in public.cannot find main method.

Q 10: What is platform?

Ans: A platform is basically the hardware or software environment in which a program runs.There are two types of platforms software and hardware.Java provides software-based platform.

Q 11: What is meant by Inheritance and what are its advantages?

Ans: Inheritance is the process of inheriting all the features from a class. The advantages of inheritance are reusability of code and accessibility of variables and methods of the super class by subclasses.

Q 12: What is the difference between superclass and subclass?

Ans: A super class is a class that is inherited whereas sub class is a class that does the inheriting.

Q 13: What all memory areas are allocated by JVM?

Ans: Heap, Stack, Program Counter Register and Native Method Stack

Q 14: What is javac ?

Ans: It produces the java byte code from *.java file.It is the intermediate representation of your source code that contains instructions.

Q 15: Can we mark constructors final?

Ans: No, Constructor cannot be declared final.

Q 16: What are two different ways to call garbage collector?

Ans: System.gc() OR Runtime.getRuntime().gc().

Q 17: What is the difference between superclass and subclass?

Ans: A super class is a class that is inherited whereas sub class is a class that does the inheriting.

Q 18: What is an abstract class?

Ans: An abstract class is a class designed with implementation gaps for subclasses to fill in and is deliberately incomplete.

Q 19: What are the states associated in the thread?

Ans: Thread contains ready, running, waiting and dead states.

Q 20: What is the difference between a constructor and a method?

Ans: A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.

A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.

Q 21: What is the difference between an Interface and an Abstract class?

Ans: An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract.

An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.

Q 22: Can we override a static method?

Ans: No, we cannot override a static method. Static means class level.

Q 23: What is synchronization?

Ans: Synchronization is the mechanism that ensures that only one thread is accessed the resources at a time.

Q 24: What is deadlock?

Ans: When two threads are waiting each other and can’t precede the program is said to be deadlock.

Q 25: Use of finalize() method in java?

Ans: finalize() method is used to free the allocated resource.

Q 26: Is it possible to overload main() method of a class?

Ans: Yes, we can overload main() method as well. But every time public static main(String[] args) will be called automatically by JVM.Other methods need to call explicitly.

Q 27: What is static in java?

Ans: Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object.

A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can’t override a static method with a nonstatic method. In other words, you can’t change a static method into an instance method in a subclass.

Q 28: Can I declare a data type inside loop in java?

Ans: Any Data type declaration should not be inside the loop. Its possible but not recommended.

Q 29: What is final class?

Ans: A final class can’t be extended ie., final class may not be subclassed. A final method can’t be overridden when its class is inherited. You can’t change value of a final variable (is a constant).

Q 30: Can we inherit the constructors?

Ans: No, we cannot inherit constructors. We can call super class constructors from subclass constructor by using super() call.

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