Saturday, January 28, 2023

String Coding Interview Questions In Java

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Q 25 What Happens When The Main Isn’t Declared As Static

Java String interview Questions and Answers with example| Immutable | Most Asked | Code Decode

When the main method is not declared as static, then the program may be compiled correctly but ends up with a severe ambiguity and throws a run time error that reads “NoSuchMethodError.”

With this we are done with the first section that is Basic Java Interview Question, Now, lets move on to our next section of Intermediate Java Interview Questions.

How To Convert String To Integer

In the java program, many times, we have to convert a string to an int. We can convert string to an integer using Integer.parseInt method as well as Integer.valueOf method.

Below I have given a java program to convert the String str to int result.


The output of the above program will be,

1 The converted intis:1234

In the above program, we have to make sure that String str should not contain any characters other than the decimal digit.

If str contains any character other than digits, it will throw the NumberFormatException.

State The Difference Between Stringbuffer And Stringbuilder In Java

StringBuffer and StringBuilder are two Java classes for manipulating strings. These are mutable objects, i.e., they can be modified, and provide various methods such as insert, substring, delete, and append, for String manipulation.

  • StringBuffer: The StringBuffer class was created by the Java Team when they realized the need for an editable string object. Nevertheless, StringBuffer has all methods synchronized, meaning they are thread-safe. Therefore, StringBuffer allows only one thread to access a method at once, so it is not possible to call StringBuffer methods from two threads simultaneously, which means it takes more time to access. The StringBuffer class has synchronized methods, making it thread-safe, slower, and less efficient than StringBuilder. The StringBuffer class was introduced in Java 1.0.
StringBuffer var = new StringBuffer 
  • StringBuilder: It was at that point that the Java Team realized that making all methods of StringBuffer synchronized wasn’t the best idea, which led them to introduce StringBuilder. The StringBuilder class has no synchronized methods. Unlike StringBuffer, StringBuilder does not offer synchronized methods, which makes it less thread-safe, faster, and more efficient. StringBuilder was introduced in Java 1.5 in response to StringBuffer’s shortcomings.
StringBuilder var = new StringBuilder 

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How To Check If String Is Palindrome In Java Using Recursion

package test /** * Java program to show you how to check if a String is palindrome or not. * An String is said to be palindrome if it is equal to itself after reversing. * In this program, you will learn how to check  * if a string is a palindrome in java using recursion * and for loop both.  * * @author Javin */publicclassPalindromeTest /**     * Java method to check if given String is Palindrome     * @param text     * @return true if text is palindrome, otherwise false     */publicstatic boolean isPalindromStringreturnfalse     }/**     * Java method to reverse String using recursion     * @param input     * @return reversed String of input     */publicstaticStringreversereturninput.charAt-1)                    +reverse -1))     }}OutputIs aaa palindrom?:trueIs abc palindrom?:falseIs bbbb palindrom?:trueIs defg palindrom?:false

Cracking the Coding Interview: 150 Programming Questions and Solutions

Q5 What Is A Singleton Class Give A Practical Example Of Its Usage

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A singleton class in java can have only one instance and hence all its methods and variables belong to just one instance. Singleton class concept is useful for the situations when there is a need to limit the number of objects for a class.

The best example of singleton usage scenario is when there is a limit of having only one connection to a database due to some driver limitations or because of any licensing issues.

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How Do You Print All Leaves Of A Binary Search Tree

You can use recursion to print all the leaves of a binary tree in Java. Since the tree is a recursive data structure, you can apply the same algorithm to the left and right subtree. You can print all leaf nodes by traversing the tree, checking each node to find if their left and right child nodes are null, and then printing that node.

Which Language Is Considered The Best For Programming

Python is the main coding language for 80% of developers. This is because Python has extensive libraries and frameworks that support a variety of applications, including AI, data science, and machine learning processes. Python is also easy for beginners to learn because of its readability and user-friendly data structures. Javascript is a top programming language for front-end developers.

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How To Check If A String Is A Palindrome

If the string is similar from the starting as well as the ending, then we can say that the string is a palindrome.

For example. madam, radar, etc.

I have given a program below which checks if the given string is palindrome or not.

The inputString’madam’isaplaindrome String.

In the above program, we are getting the reversed string of the inputString.

If the reversedString and the inputString is the same, then the string is a palindrome.

Faqs On Java String Interview Questions

Java coding interview questions || Print duplicate occurrences of string in java

Q1. What are the most common Java String Interview Questions?

Some important questions are â What is String in Java? Whatâs the difference between String in C language and String in Java? Whatâs the String pool in Java? Whatâs the intern method?

For more questions, just go over the questions listed above in the article.

Q2. How are Strings stored in memory Java?

In Java, Strings are stored on the heap area in a different memory location called the String Constant pool. String Constant pool refers to a separate block of memory where all the String variables are stored.

Q3. What is == and equals in Java String interview questions?

Both are used to compare two objects in Java. The difference is that == check whether two objects point to the same memory location while equals decides the comparison of values in the objects.

Q4. How many bytes are there in a String?

Eight bits of memory storage are allocated to store each character in the String , while each byteâs value is undetermined.

Q5. Is String a data type?

A String is usually considered a data type. It is often carried out as an array data structure of bytes that stores a sequence of elements, typically characters, using some character encoding.

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Write A Java Program That Illustrates Merge Sort

Merge sort is one of the most efficient sorting algorithms. It works on the principle of âdivide and conquerâ. It is based on the idea of breaking down a list into several sub-lists until each sub-list consists of a single element, and then merging those sub-lists in a manner that results in a sorted list. The following example code shows one way to use merge sort:

publicclassMergeSort int merged =mergeSort for}publicstaticintmergeTwoSortedArrayselse}if}if}return sorted }publicstaticintmergeSortint mid =/2 int fh =mergeSort int sh =mergeSort int merged =mergeTwoSortedArrays return merged }}

Why Is String Immutable In Java

String is immutable in Java because this offers several benefits:

  • String pool is possible because String is immutable in Java.
  • It increases security because any hacker canât change its value and itâs used for storing sensitive information such as a database username or password.
  • Since String is immutable, itâs safe to use in multi-threading and you donât need any synchronization.
  • Strings are used in Java class loaders and immutability provides assurance that the correct class is getting loaded by the ClassLoader class.

Learn more about why String is immutable in Java.

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Q 56 How To Handle Exceptions In Spring Mvc Framework

Spring MVC has two approaches for handling the exceptions:

  • Exception handler method: In this kind of exception handling, the user will get the @ExceptionHandler annotation type used to annotate a method to handle exceptions.
  • XML Configuration: The user can use the SimpleMappingExceptionResolver bean in Springs application file and map the exception.

What Is Cors In Mvc And How It Works


CORS stands for Cross-Origin Resource Sharing. It is a W3C standard and HTTP-header-based mechanism. It permits a server to indicate any other origins instead of the requested one. In other words, it enables one website to access the resources of another website using JavaScript.

It supports secure cross-origin requests and transfers data between servers and browsers. Advanced browsers use CORS in APIs. It is flexible and safe in comparison to JSONP . It provides better web service integration.

While using the MVC to enable CORS, the same CORS service can be used but we cannot use the same CORS middleware. We can use a particular CORS for a particular action, for a particular controller, and globally for all controllers.

A pre-flight check is sent by the browser to the server which ensures that the server will permit the actual request or not. For example, invoking the URL through .

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Question : What Are Access Specifiers In Java

There are four access specifiers which the candidate should understand. There are the following qualifiers: public, private, protected and standard.

Public qualifiers allow access to any class or through any method . In contrast, private specifiers only allow access within the specified class itself. Protected ones open access that somehow correlates with the class â either from within the class, from a subclass, or simply from the same package. Finally, default denotes a standard area and allows access from only one package.

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How Do You Create A Functional Interface

An interface with exactly one abstract method is called a functional interface. The major benefit of functional interfaces is that you can use lambda expressions to instantiate them and avoid using bulky anonymous class implementation. The @FunctionalInterface annotation indicates a functional interface, as shown in the following example code:


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Q 29 What Are Brief Access Specifiers And Types Of Access Specifiers

Access Specifiers are predefined keywords used to help JVM understand the scope of a variable, method, and class. We have four access specifiers.

  • Public Access Specifier

There are two types of constructors in Java.

Parameterized Constructors: Parameterized constructor accepts the parameters with which users can initialize the instance variables. Users can initialize the class variables dynamically at the time of instantiating the class.

Default constructors: This type doesnt accept any parameters rather, it instantiates the class variables with their default values. It is used mainly for object creation.

Show Examples Of Overloading And Overriding In Java

Reverse a String – Java Interview Coding Challenge #3 [Java Brains]

When a class has two or more methods with the same name, they are called overloaded methods. The following example code shows as overloaded method called print:


When a superclass method is also implemented in the child class, itâs called overriding. The following example code shows how to annotate the printname method thatâs implemented in both classes:


Test yourself by guessing the output of the following code snippets.

String s1 ="abc" String s2 ="abc" System.out.println 

The output of the given statement is false because the + operator has a higher precedence than the == operator. So the given expression is evaluated to âs1 == s2 is:abcâ == âabcâ, which is false.

String s3 ="JournalDev" int start =1 char end =5 System.out.println) 

The output of the given statement is ourn. The first character is automatically type cast to int. Then, since the first character index is 0, it will start from o and print until n. Note that the String substring method creates a substring that begins at index start and extends to the character at index end – 1.

HashSet shortSet =newHashSet forSystem.out.println) 

No output. This code results in an infinite loop if the flag is true and the program exists if the flag is false. The finally block will never be reached.

String str =null String str1="abc" System.out.println| str.equals) 
String x ="abc" String y ="abc" x.concat System.out.print 

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What Is The Difference Between Gaurav Kukadeequals And Strequals

Both look the same, and it will check if the content of the string variable str is equal to the string “Gaurav Kukade” or not.

But their behavior will change suddenly when a string variable str = null. The first code snippet will return false, but the second code snippet will through a NullPointerExpection.

Below I have given a program which uses both ways to compare string using equals method.

Exception inthread”main”java.lang.NullPointerExceptionat StringNullExample.main

We can see the above output, for first code snippet it is print false but for the second code snippet, it is throwing NullPointerException.

It is one of the most important tricks to avoid the null pointer exception in java string. So this question is important.

Can We Compare String Using The == Operator What Is The Risk

Yes, of course, we can compare String using the == operator. But when we are comparing string using the == operator, we are comparing their object reference, whether these string variables are pointing towards the same string object or not.

Most of the time, developers want to compare the content of the strings, but mistakenly they compare strings with == operator, instead of equals method, which leads to an error.

Below, I have given a program, which shows the string comparison using the == operator and equals method.


In case 1, we are comparing firstString and secondString using the equals to operator , since both the variables are pointing towards the same string object, it will print true.

In case 2, we are comparing firstString and thirdString using the equals to operator i.e. == since both the variables are not pointing towards the same string object, it will print false.

You can see, for thirdString, we are using the new keyword, which creates a new object in Java heap memory.

In case 3, we are comparing firstString and thirdString using equals method. Even if both are the different string object, it has the same content hence it is printing true.

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How Do You Reverse A String In Java

There is no reverse utility provided in Java. Hiring managers might ask this question to determine your knowledge of Java and your problem-solving skills. You can create a character array from the string and iterate it from the end to the beginning. You can append the characters to a string builder and finally return the reversed string.

Example answer:

Q9 How Do You Check If A String Is Empty

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Java String class has a unique method for checking if the String is empty or not.

isEmpty method is used to internally check whether the length of a String is zero. If itâs zero, it means the String is empty, and the isEmpty method will come back true.

And if the length isnât zero, then the isEmpyt method will come back false.

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Q16 What Are Java Packages Whats The Significance Of Packages

Ans: In Java, package is a collection of classes and interfaces which are bundled together as they are related to each other. Use of packages helps developers to modularize the code and group the code for proper re-use. Once code has been packaged in Packages, it can be imported in other classes and used.

In Java What Is The Difference Between String Stringbuilder And Stringbuffer

A string represents a sequence of characters. In Java, strings are objects. Java has provided the StringBuffer and StringBuilder classes that can be used for string manipulation.

StringBuffer StringBuilder
StringBuffer is synchronized . It means two threads cant call the methods of StringBuffer simultaneously. StringBuilder is non-synchronized . It means two threads can call the methods of StringBuilder simultaneously.
Less efficient
Introduced in Java 1.5

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What Distinguishes A Great Software Engineer From A Good One Do You Feel You Have Those Qualities

Well, you dont want to brag, but Just be honest, where are you when it comes to your skills, and where you want to be. Show a recruiter that you want to learn about the new technologies every day, that youre aware that the learning process never ends. Be positive about your knowledge, but aware of your lack of expertise. Applicants should showcase their enthusiasm for development and talk about any projects theyre working on outside of a job.

Faqs On Java 8 Interview Questions

Java 8 Stream API and String | Capgemini Mock L1 Coding Interview

Q1. What are the features of Java 8?

Java 8 offers these features for Java programming: Lambda Expression and Virtual Extension Methods, Date and Time API, Nashorn JavaScript Engine, and Enhanced Security.

Q2. What is the average salary of front-end software engineers?

The average salary of a front-end developer ranges from $116,737 to $119,224.

Q3. What can you do with Java 8?

Java 8 is one of the latest releases of the Java programming language. It comes with enormous features such as date and time APIs, Java stream API, functional interfaces, a new JavaScript engine, Nashorn, and many more.

Q4. How to prepare for Java 8 interview questions for 10 years of experienced developers?

Firstly, to prepare for Java 8 interview questions for coding or tech interviews, be thorough with Java 8 features and their fundamentals. Study the most significant Java 8 features such as Lambda Expressions, Method References, Optional, Functional Interface, Default methods, Nashorn, JavaScript Engine, Stream API, and Date API.

Q5. What is lambda in Java 8?

A Lambda expression in Java 8 is a helpful feature that allows you to represent one method interface using an expression clearly and concisely. It accepts parameters and outputs a value. It aids in iterating, filtering, and extracting data from a collection.

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