Java Interview Questions

Front 1

What do you know about Java

Back 1

Java is a high level programming language originally developed by Sun Micro systems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX.

Front 2

What are the supported platforms by Java Programming Language?

Back 2

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.

Front 3

List Any Five Features of Java

Back 3

Some features include Object Oriented, Platform Independent, Robust, Interpreted, Multi-Threaded

Front 4

Why is Java Architectural Neutral

Back 4

It's compiler generates an architecture-neutral object file format, which makes the compiled code to be executable on many processors, with the presence of Java runtime system.

Front 5

How did Java enable High Performance

Back 5

Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler is a program that turns Java bytecode, which is a program that contains instructions that must be interpreted into instructions that can be sent directly to the processor.

Front 6

Why is Java considered dynamic?

Back 6

It is designed to adapt to an evolving environment. Java programs can extensive amount of run-time information that can be used to verify and resolve accesses to objects in run-time.

Front 7

What is Java Virtual Machine and how is it considered in context of Java's platform independent feature?

Back 7

When Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by Virtual Machine (JVM) on whichever platform it is being run.

Front 8

List two Java IDEs?

Back 8

Netbeans, Eclipse, Android Studio

Front 9

List some Java keywords(unlike C, C++? keywords)?

Back 9

Some Java keywords are import, super, finally, etc.

Front 10

What do you mean by Object?

Back 10

Object is a runtime entity and it's state is stored in fields and behavior is shown via methods. Method operate on an object's internal state and serve as the primary mechanism for object-to-object communication.

Front 11

Define class?

Back 11

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.

Front 12

What kind of variables a class can consist of?

Back 12

A class can consist of Local variable, instance variable, and class variables.

Front 13

What is Local Variable?

Back 13

Variables defined inside methods, constructors or blocks are called local variables. The variables will be declared and initial used within the method and it will destroyed when the method has completed.

Front 14

What is Instance Variable?

Back 14

Instance variable are variable within a class but outside any method. These variable are instantiated when the class is loaded.

Front 15

What is a Class Variable?

Back 15

These are variable declared with in a class, outside any method, with static keyword.

Front 16

What is Singleton Class?

Back 16

Singleton class control object creation, limiting the number to one but allowing the flexibility to create more objects if the situation changes.

Front 17

What do you mean Constructor?

Back 17

Constructor gets invoked when a new object is created. Every class has a constructor. If we do not explicitly write a constructor for a class the Java compiler builds a default constructor for that class.

Front 18

List the three steps for creating an Object for a class?

Back 18

An Object is first declared, then instatiated and then it is initialized.

Front 19

What is the default value of byte data type in Java?

Back 19

Default value of byte data type is 0.

Front 20

What is the default value of float and double data type in Java?

Back 20

Default value of float and double data type in different as compared to C/C++. For float it's 0.0f and for double 0.0d.

Front 21

When a byte data type is used?

Back 21

This data type is used to save space in large arrays, mainly in place of intergers, since a byte is four times smaller.

Front 22

When a byte data type is used?

Back 22

This data type is used to save space in large arrays, mainly in place of intergers, since a byte is four times smaller.

Front 23

What is a static variable?

Back 23

Class variables also known as static variables are declared with the static keywords in a class, but outside a method, constructor or a block.

Front 24

What do you mean by Access Modifier?

Back 24

Java provides access modifiers to set access levels for classes, variables, methods and constructors. A member has package or default accessibility when no accessibility modifier is specified.

Front 25

What is protected access modifier?

Back 25

Variables, methods and constructors which are declared protected in a superclass can be accessed only by the superclasses in other packages or any class within the package of the protected members class.

Front 26

What do you mean by synchronized Non Access Modifier?

Back 26

Java provides these modifiers for providing functionalities other than Access Modifiers, synchronized used to indicate that method can be accessed by only one thread at a time.

Front 27

According to Java Operator precedence, which operator is considered to be with highest precedence?

Back 27

Post fix operators i.e. ()[]. Is at the highest precedence.

Front 28

Variables used in a switch statement can be used with which data types?

Back 28

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

Front 29

When parseInt() method can be used?

Back 29

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

Front 30

Why is String class considered immutable?

Back 30

The String class is immutable, so that once it is created a String object cannot be changed. Since String is immutable it can safely be shared between many threads, which is considered very important for multi threaded programming.

Front 31

Why is StringBuffer called mutable?

Back 31

The String class is considered as immutable, so that once it is created a String object cannot be changed. If there is a necessity to make a lot of modifications to Strings of characters then String buffer should be used.

Front 32

What is the difference between StringBuffer and StringBuilder class?

Back 32

Use StringBuilder whenever possible because it is faster than StringBuffer. But, if thread safety is necessary then use StringBuffer objects.

Front 33

Which package is used for pattern matching with regular expressions?

Back 33

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

Front 34

Java.util.regex consists of which classes?

Back 34

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

Front 35

What is finalize() method?

Back 35

It is possible to define a method that will be called just before an objects final destruction by the garbage collector.. This method is called finalize(),and it can be used to ensure that an object terminates cleanly.

Front 36

What is an Exception?

Back 36

An exception is a problem that arises during the execution of a program. Exceptions are caught by handlers positioned along the threads method invocation stack.

Front 37

What do you mean by Checked Exceptions?

Back 37

It is an exceptions that is typically a user error or a problem that cannot be foreseen by the programmer.. For example, if a file is to be opened, but the file cannot be found, an exception occurs. These exceptions cannot simply be ignored at the time of compilation.

Front 38

Explain Runtime Exceptions?

Back 38

It is an exception that occurs that probably could have been avoided by the programmer. As opposed to checked exceptions, runtime exceptions are ignored at the time of compilation.

Front 39

Which are the two sub classes under Exception class?

Back 39

The Exception class has two main sub classes : IOException class and RunTimeException Class.