Important Java variables interview questions and answers

As a programmer, it is essential to have a strong understanding of variables and how they are used in Java. In this blog post, we will cover some of the most important Java variables interview questions and answers for both freshers and experienced programmers.

If you are not learnt about java basics, find our best collection of core java basics interview questions and answers.

We will start by looking at some basic interview questions on variables in java, such as what they are and how they are used. We will then move on to more advanced topics, such as the difference between instance variables, static variables, and local variables, and the difference between the final, volatile, strong, weak, and soft keywords.

In addition to the java variables interview questions and answers, we will also provide examples of how to use variables in Java, so you can see how they work in practice. Whether you are a beginner or an experienced programmer, this blog post will provide you with the knowledge you need to confidently answer interview questions on variables in java.

For your future reference, we have made a compilation of these questions in the PDF format. You can use the below button to download the Java variables interview questions PDF file.

Before Jumping to the interview preparation questions, we strongly recommend going through the tutorial on variables in Java to have a better understanding about it.

Java variables interview questions and answers for freshers

What is a variable in Java?

A variable in Java is a location in memory where a value can be stored and accessed. A variable has a name, a type, and a value. For example:

int x; // Declares a variable of type int with the name "x"
x = 10; // Assigns the value 10 to the variable x

What are the different types of variables in Java?

In Java, there are four types of variables:

• Local variables: These are variables that are defined within a method and are only accessible within that method.
• Instance variables: These are variables that are defined within a class, but outside of any method. They are associated with an instance of the class and are accessible from any method of the class.
• Static variables: These are variables that are associated with a class, rather than a specific instance of the class. They are often used to store values that are common to all instances of a class.
• Parameters: These are variables that are passed to a method as arguments when the method is called.

What is the difference between a local variable and an instance variable in Java?

A local variable is a variable that is defined within a method and is only accessible within that method. An instance variable is a variable that is defined within a class, but outside of any method. It is associated with an instance of the class and is accessible from any method of the class.

For example:

public class MyClass {
// Instance variable
private int x;

public void myMethod() {
// Local variable
int y = 0;
}
}

Can you give an example of how to declare and initialize a static variable in Java?

To declare a static variable in Java, you use the static keyword before the type of the variable. The variable is then initialized at the point of declaration. For example:

public class MyClass {
// Declares and initializes a static variable
static int x = 10;
}

To access a static variable from another class, you use the name of the class followed by the name of the variable. For example:

int value = MyClass.x;

What is the difference between a primitive type and a reference type in Java?

In Java, there are two types of variables: primitive and reference.

• Primitive variables are variables that store values of primitive types such as int, char, and boolean. They are stored directly on the stack, which means they are created and destroyed very quickly.
• Reference variables, on the other hand, store references to objects. They are stored on the heap, which means they are created and destroyed more slowly. Examples of reference types include String, Array, and Object.

Can you give an example of how to declare and initialize a final variable in Java?

A final variable in Java is a variable that cannot be changed once it has been initialized. To declare a final variable, you use the final keyword before the type of the variable. The variable must then be initialized at the point of declaration or in a static initializer block.

For example:

public class MyClass {
// Declares and initializes a final variable
final int x = 10;
}

What is the difference between the final and const keywords in Java?

The final keyword in Java is used to declare a variable that cannot be changed once it has been initialized. It can be used with both primitive types and reference types.

final int x = 10; // Declares a final int variable
final String str = "Hello"; // Declares a final String variable

The const keyword, on the other hand, is not a keyword in Java. It is a reserved word in some other programming languages, but it is not used in Java.

Can you give an example of how to declare and initialize a variable with the var keyword in Java?

The var keyword in Java is a type inference keyword that was introduced in Java 10. It allows you to declare a variable without specifying its type explicitly. The type of the variable is then inferred from the value that is assigned to it.

To declare a variable with the var keyword, you use the following syntax:

var variableName = value;

For example:

var x = 10; // Declares a variable of type int
var str = "Hello"; // Declares a variable of type String

Note that the var keyword can only be used to declare local variables and parameters. It cannot be used to declare instance variables, static variables, or final variables.

Can you give an example of how to declare and initialize a variable with a compound type in Java?

A compound type in Java is a type that is made up of multiple other types. The two most common compound types are arrays and classes.

To declare and initialize an array variable in Java, you use the following syntax:

type[] arrayName = {value1, value2, …};

For example:

int[] numbers = {1, 2, 3, 4, 5}; // Declares and initializes an array of integers
String[] names = {"Alice", "Bob", "Charlie"}; // Declares and initializes an array of strings

To declare and initialize a class variable in Java, you use the following syntax:

className variableName = new className(constructor arguments);

For example:

Point point = new Point(10, 20); // Declares and initializes a Point object

Note that the class must have a constructor that takes the specified arguments in order to create an instance of the class.

What Are the Rules to be followed while Naming Java Variables?

In Java, there are a few rules that you must follow when naming variables:

• Variable names must begin with a letter, dollar sign ($), or underscore (_).
• Variable names cannot contain spaces or special characters other than dollar sign ($), or underscore (_).
• Variable names are case-sensitive. For example, age and Age are considered to be different variables.
• Variable names cannot be the same as Java keywords. For example, you cannot use class or int as a variable name.
• It is recommended to use camelCase or snake_case when naming variables. CamelCase is a naming convention where the first letter of each word is capitalized except the first word, which is written in lowercase. Snake_case is a naming convention where words are separated by an underscore (_).

For example:

// Valid variable names
int age;
String firstName;
double hourlyWage;

// Invalid variable names
int Age; // Begins with a capital letter
int first-name; // Contains a special character
int first name; // Contains a space
int class; // Is a Java keyword

Where Java stores the variables in memory?

In Java, variables are stored in different places depending on their type and scope.

• Primitive variables (such as int, char, and boolean) are stored on the stack. The stack is a part of the memory that is used to store temporary data, such as method arguments and local variables. The stack is created when a program starts and is destroyed when the program ends.
• Reference variables (such as String, Array, and Object) are stored on the heap. The heap is a part of the memory that is used to store objects. The heap is created when a program starts and is destroyed when the program ends.
• Instance variables and static variables are stored in the same place as reference variables (on the heap), but they are associated with a class rather than a specific instance of the class.
• Parameters are stored on the stack like local variables. They are created when a method is called and are destroyed when the method returns.

It’s important to note that the exact location of variables in memory is determined by the Java Virtual Machine (JVM) and may vary from one implementation to another.

Java variables interview questions and answers for experienced

Below are the set of Java practice questions on variables for 2 years, 5 years, 7 years or 10 years experienced professional. With the in-depth knowledge, experienced candidate can easily answer any tricky java interview questions on variables. Hope you will get that confidence with the below set of practice questions on variables.

Can you explain the difference between instance variables, static variables, and local variables in terms of visibility and lifetime?

• Instance variables are variables that are defined within a class, but outside of any method. They are associated with an instance of the class and are accessible from any method of the class.
• Static variables are variables that are associated with a class, rather than a specific instance of the class. They are often used to store values that are common to all instances of a class.
• Local variables are variables that are defined within a method and are only accessible within that method.
• In terms of visibility, instance variables and static variables are both visible to all methods of the class. Local variables, on the other hand, are only visible within the method in which they are defined.
• In terms of lifetime, instance variables and static variables are created when an instance of the class is created and destroyed when the instance is garbage collected. Local variables, on the other hand, are created when the method is called and destroyed when the method returns.

Can you explain the difference between the final and volatile keywords in Java?

• The final keyword in Java is used to declare a variable that cannot be changed once it has been initialized. It can be used with both primitive types and reference types.
• The volatile keyword in Java is used to declare a variable that can be modified by multiple threads concurrently. It is often used to ensure that the value of a variable is always up-to-date when accessed by multiple threads.
• The final keyword is used to ensure that the value of a variable does not change, while the volatile keyword is used to ensure that the value of a variable is always up-to-date when accessed by multiple threads.

Can you explain the difference between an array and an ArrayList in Java?

• An array in Java is a collection of values of the same type that are stored in contiguous memory locations. An array has a fixed size, which means that you cannot add or remove elements from it once it has been created.
• An ArrayList in Java is a resizable array that is implemented using an array as the underlying data structure. An ArrayList has a variable size, which means that you can add and remove elements from it at any time.
• In terms of performance, arrays are generally faster than ArrayLists for basic operations such as accessing and modifying elements. However, ArrayLists are more flexible and easier to use in situations where the size of the collection may change frequently.

Can you explain the difference between a stack and a heap in Java?

• The stack in Java is a part of the memory that is used to store temporary data, such as method arguments and local variables. The stack is created when a program starts and is destroyed when the program ends.
• The heap in Java is a part of the memory that is used to store objects. The heap is created when a program starts and is destroyed when the program ends.
• In terms of allocation and deallocation, variables on the stack are created and destroyed very quickly because they are stored in contiguous memory locations. Variables on the heap, on the other hand, are created and destroyed more slowly because they are stored in non-contiguous memory locations.
• In terms of accessibility, variables on the stack are only accessible within the method in which they are defined. Variables on the heap, on the other hand, are accessible from any part of the program.

Can you explain the difference between a strong reference, a weak reference, and a soft reference in Java?

• In Java, a strong reference is a reference that is used to keep an object alive. As long as there is at least one strong reference to an object, the object will not be garbage collected.
• A weak reference is a reference that is used to keep an object alive, but only as long as there are strong references to the object. If there are no strong references to an object, the object may be garbage collected even if there are weak references to it.
• A soft reference is a reference that is used to keep an object alive, but only as long as the system is not running low on memory. If the system needs to free up memory, it may clear soft references to objects even if there are strong or weak references to them.
• In general, strong references are the most common type of reference and are used to keep objects alive for the duration of the program. Weak references are used in cases where it is useful to keep an object alive as long as there are strong references to it, but it is not essential. Soft references are used in cases where it is useful to keep an object alive as long as the system is not running low on memory, but it is not essential.

Can you explain the difference between a shallow copy and a deep copy in Java?

• A shallow copy in Java is a copy of an object that creates a new object and copies the values of the object’s instance variables to the new object. However, if the object contains references to other objects, the copy only copies the references and not the objects themselves.
• A deep copy in Java is a copy of an object that creates a new object and recursively copies the values of the object’s instance variables and the objects that they refer to.
• In general, a shallow copy is sufficient when the object being copied does not contain references to other objects. A deep copy is necessary when the object being copied contains references to other objects that need to be copied as well.

Can you explain the difference between == and .equals() in comparing Java variables?

• The == operator in Java is used to compare the values of two variables. If the variables are of a primitive type, it compares the values directly. If the variables are of a reference type, it compares the references rather than the objects themselves.
• The .equals() method in Java is used to compare the values of two objects. It is a method of the Object class, which means that it is inherited by all objects in Java. The .equals() method compares the values of the objects based on their type and the contents of the objects.

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Understanding Java variables concepts is an essential skill for any programmer to clear interview questions on variables in java. In this blog post, we have covered a variety of Java variables interview questions and answers, including questions for both freshers and experienced programmers.

We have discussed the different types of variables in Java, such as primitive variables, reference variables, instance variables, static variables, and local variables. We have also looked at the difference between the final, volatile, strong, weak, and soft keywords, a stack and a heap, a shallow copy and a deep copy, and == and .equals().

We hope that this blog post has provided you with a solid foundation in Java variables and that you feel more confident about answering Java variables interview questions. Remember, the more you practice and the more you learn, the better you will become at using variables in Java.