Java Interview Question and Answers

Java Interview Question and Answers

1-       What is Java?

A-      Java is a high level programming language originally developed by Sun Microsystems and released in 1995.

2-       Why called Java is platform independent language?

A-      Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX/LINUX (like HP-Unix, Sun Solaris, Redhat Linux, Ubuntu, CentOS, etc.). So that is why called java is platform independent language.

3-       List any five features of Java?

A-     Some features include Object Oriented, Platform Independent, Robust, Interpreted, Multi-threaded.

4-       List two Java IDE’s?

A-      Netbeans, Eclipse, etc.

5-       What is JVM (Java Virtual Machine)?

A-      Java Virtual Machine is a process of virtual machine that can execute Java bytecode. Each Java source file is compiled into a bytecode file, which is executed by the JVM.

6-       What is JDK (Java Development Tool Kit)?

A-      The Java Runtime Environment (JRE) is basically the Java Virtual Machine (JVM) where your Java programs are being executed.

7-       What is JRE (Java Run-Time Environment)?

A-      The Java Development Kit (JDK) is the full featured Software Development Kit for Java, including the JRE, the compilers and tools (like JavaDoc, and Java Debugger), in order for a user to develop, compile and execute Java applications.

8-       What are the Data Types of Java?

A-      The eight primitive data types supported by the Java programming language are: • byte • short • int • long • float • double • boolean • char

9-       What is Object?

A-      A Java object is a combination of data and procedures working on the available data. An object has a state and behavior. The state of an object is stored in fields (variables), while methods (functions) display the object's behavior. Objects are created from templates known as classes. In Java, an object is created using the keyword "new".

10-   What is class?

A-      A class is a blue print from which individual objects are created. A class can contain fields and methods to describe the behavior of an object.

11-   What kind of variables a class can consist of?

A-      A class consists of Local variable, instance variable and class variables.

12-   What is Method Overriding and Overloading in java?

A-      Method overloading in Java occurs when two or more methods in the same class have the exact same name, but different parameters.

 On the other hand, method overriding is defined as the case when a child class redefines the same method as a parent class. Overridden methods must have the same name, argument list, and return type.

13-   What is OOP’s?

A-      Object-Oriented Programming is a paradigm that provides many concepts such as inheritance, data binding, polymorphism, etc. The main aim of object-oriented programming is to implement real-world entities for example  abstraction, encapsulation, inheritance, and polymorphism .

14-   Does Java support multiple inheritances?

A-      No, Java does not support multiple inheritance. Each class is able to extend only on one class, but is able to implement more than one interfaces.

15-   What is the default value of datatypes in Java?

A-      Default value of Byte datatype is 0.

B-       Default value of Float datatype is 0.0f.

C-       Default value of Double datatype is 0.0d.

16-   What do you mean by Access Modifier?

A-     Java provides access modifiers to set access levels for classes, variables, methods and constructors.

17-   Variables used in a switch statement can be used with which datatypes?

A-     Variables used in a switch statement can only be a byte, short, int, or char.

18-   When parseInt method can be used?

A-     This method is used to get the primitive data type of a certain String.

19-   Which package is used for pattern matching with regular expressions?

A-      Java.util.regex package is used for this purpose.

20-   Java.util.regex consists of which classes?

A-     Java.util.regex consists of three classes − Pattern class, Matcher class and PatternSyntaxException class.

21-   Which are the two subclasses under Exception class?

A-     The Exception class has two main subclasses: IOException class and RuntimeException Class.

22-   When throws keyword is used?

A-     If a method does not handle a checked exception, the method must declare it using the throws keyword. The throws keyword appears at the end of a method's signature.

23-   When throw keyword is used?

A-     An exception can be thrown, either a newly instantiated one or an exception that you just caught, by using throw keyword.

24-   What is an Interface?

A-     An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.

25-   What exactly is a .class file? A. It's a binary file (sequence of 0s and 1s).

A-     If you are using Unix or OS X, you can examine its contents by typing od -x HelloWorld.class at the command prompt. This displays the results in hexadecimal (base 16). In deference to Java's name, the first word of every .class file is cafe.

26-   Why is the type for real numbers called double?

A- Historically, the type for floating point numbers was float, but they had limited accuracy. The type double was introduced as a floating point type with twice as much accuracy.

27-   Why doesn't the statement if (a <= b <= c) work?

A-     The <= operator cannot be chained. Instead, use if (a <= b && b <= c).

28-   What are pass by reference and pass by value?

A-     When an object is passed by value, this means that a copy of the object is passed. Thus, even if changes are made to that object, it doesn’t affect the original value. When an object is passed by reference, this means that the actual object is not passed, rather a reference of the object is passed. Thus, any changes made by the external method, are also reflected in all places.

29-   What is the difference between processes and threads?

A-     A process is an execution of a program, while a Thread is a single execution sequence within a process. A process can contain multiple threads. A Thread is sometimes called a lightweight process.

30-   What is the difference between a synchronized method and a synchronized block?

A-     In Java programming, each object has a lock. A thread can acquire the lock for an object by using the synchronized keyword. The synchronized keyword can be applied in a method level or block level of code .

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