Java Tutorial Index

Java Tutorial Java Features C++ vs Java Java History Java Hello World Java Development Kit Java Runtime Environment Java Virtual Machine Difference between JDK, JRE, and JVM Memory Areas in Java Java Operators Java Keywords Primitive Data Types Variables

Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java Program to find and replace characters on string in java Program to find the duplicate characters in a string Program to check whether a given character is present in a string or not Java Program to Print Permutations of String Java program to find frequency of characters in a string Java Program to remove duplicate characters in a string Java Program to Sort an Array of 0's, 1's, and 2’s | Dutch National Flag Problem in Java Java Program to print even and odd numbers using 2 threads Java Program to generate binary numbers Java program to count the occurrences of each character Java Program to Add Digits Until the Number Becomes a Single Digit Number Program to Implement FLAMES Game in Java Packages Program in java Pangram Program in Java Java program to print matrix in Z form CRC Program in Java Star Program in Java Structure of Java Program RMI program in Java Caesar Cipher Program in Java Java Programming certification Round Robin Scheduling Program in Java Java Program to find the smallest element in a tree Program to Find Square Root of a Number Without sqrt Method in Java Program to Find the Common Elements between two Arrays in Java Automorphic Number Program in Java

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java Java Program to Create Set of Pairs Using HashSet

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Methods in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Enumeration Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize Java Garbage Collection Interview Questions

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java file Reader Java Buffer Reader Java file Writer Java BufferedWriter Java InputStreamReader Scanner in Java Java StringReader Java StringReader Class Java StringWriter Class Java PrintWriter Java File Java Read File Line By Line Java FileInputStream Java FileOutputStream Java Create File Java Delete File Java Open File Java Read File to String Java copy file Jar File in Java Java FileNotFoundException

Serialization

Java Serialization Java transient

Networking

Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket

AWT

Java AWT

Swing

Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java Deque in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java

Java JDBC

Java JDBC Tutorial JDBC Architecture Types of JDBC Drivers JDBC vs ODBC Java Database Connectivity with MySQL Java Database Connectivity with Oracle Statements in java Prepared statement in Java Resultset in java Java ResultSetMetaData DatabaseMetaData in Java Callable Statement in Java Transaction Management in Java Design of JDBC

Java Differences

Java vs DotNET Java vs JavaScript Kotlin vs Java Java vs C++ C# vs Java Java float vs double Java vs Scala Java vs Go Java vs Golang Java Extends vs Implements Java vs Node.js Static vs Non-static in Java int vs Integer in Java Java protected vs private Java vs Dot Net Stack vs Heap in Java Java Array vs ArrayList Java SE vs EE Class vs Object in Java Java vs Bedrock Difference between = = and equals ( ) in java Difference between C, C++, java HashMap Vs HashTable Checked vs Unchecked Exceptions in Java Difference between print() and println() in Java Differences between Lock and Monitor in Java Concurrency Differences between Set and List in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Difference between String and Char Array in Java Differences between Byte Code and Machine Code Difference between String Tokenizer and split Method in Java Difference between JIT and JVM in Java Difference Between Data Hiding and Abstraction in Java Difference Between BufferedReader and FileReader Difference Between Thread.start() and Thread.run() Difference between Aggregation and Composition in Java Difference between Constructor and Method in Java Difference between next() and nextline() in Java Difference between Static and Instance Methods in Java Differences and Similarities between HashSet, LinkedHashSet and TreeSet in Java Different Ways to Print Exception Message in Java Different Ways to Take Input from User in Java Difference Between Access Specifiers and Modifiers in Java Difference Between Java and PHP Difference Between replace() and replaceall() in Java Difference between this and super in Java Generics vs Wildcard in Java

How to

How to convert String to String array in Java How to find length of integer in Java How to get Day Name from Date in Java How to open the Java control panel How to resolve Illegal state exceptions in Java How to reverse a linked list in java How to encrypt password in Java How to calculate time complexity of any program in Java How to check version of java in Linux How to enable java in chrome How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to add double quotes in a string in Java How to convert list to String in Java How to call a method in Java How to Set Environment Variables for Java How to sort an array in Java How to Create Immutable Classes in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to Create Singleton Class in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to find the length of an Array in Java How to Read Java JSON file How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to import packages in Java How to run applet Program in Java How to take Array Input in Java How to call static method in Java How to compare characters in Java How to compare dates in Java How to create a linked list in Java How to download Eclipse for Java How to get ASCII value of char in Java How to get the current date and time in Java How to handle NullPointerException in Java How to initialize string array in Java How to Install Java on MAC How to run java program in ubuntu How to find characters with the maximum number of times in a string java How to Set Java_home in Linux How to Split the String in Java with Delimiter How to take Multiple String Input in Java using Scanner class How to uninstall the Java in Ubuntu How to Update Java How to add Elements in Array in Java How to avoid deadlock in java How to Split String by Comma in Java How to remove special characters from String in Java How to remove last character from String in Java How to Read XML Files in Java How to download and install Eclipse in Windows How to Create an API in Java How to Round Double Float up to Two Decimal Places in Java How to create a mirror image of a 2D array in Java How to set timer in Java How to make Java Projects How to Create Different Packages for Different Classes in Java How to run Java program in command prompt How to run Java program in Eclipse How to calculate time difference in Java How to stop execution after a certain time in Java How to check data type in Java How to Reduce Time Complexity in Java How to check if date is valid in Java How many ways to create object in Java How to add 4 Hours to the Current Date in Java How to add 4 Years to the Current Date in Java How to add 6 Months to the Current Date in Java How to add 24 Hours to Date in Java How to Assign Static Value to Date in Java How to check Date is Greater in Java How to check Date Null in Java How to check valid date in Java How to Iterate List in Java How to increment and decrement date using Java How to Create a Generic List in Java How to compare two dates in different format in Java How to compare three dates in Java How to override toString() method in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Type Annotations in Java Java Stringjoiner Class Parallel Arrays Sort in Java Bifunction in java 8 Java 8 filters list Java 8 Consumer Interface in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java 12

What’s new in Java 12

Java 13

Java 13 New Features

Java 14

New Features of Java 14

Java 15

What’s New in Java 15

Java 16

Java 16

Java 17

What is new in Java 17

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.fma() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Java Keywords

Reserved Keywords in Java Java Case Keyword Java Class Keyword Java Continue Keyword Java Default Keyword Java Double Keyword Java Else Keyword Java Enum Keyword Java Extends keyword Java Finally Keyword Java Char Keyword Contextual keywords in Java Java Break Keyword Volatile keyword in Java Java Boolean Keyword Java Byte Keyword The final Keyword in Java Java For Keyword Java Float Keyword Java Instanceof Keyword Java If Keyword Java Int Keyword Java Import Keyword Java Package Keyword Java Public Keyword Java Implements Keyword Java Private keyword Java Protected Keyword Java Short Keyword Java Long Keyword Java Interface Keyword Java Try Keyword Java New Keyword Java Return Keyword Java Null Keyword this keyword in Java

Java Questions

What are Array strings in Java What is String in Java? What is string in Java why it's immutable What is advance Java? What is interpreter in Java? What is anagram in Java? How Many Ways to Create Objects in Java How annotations work in Java What is Core Java Why to use Enum in Java

Misc

List all files in a Directory in Java Nonagonal number in Java Null Pointer Exception in Java Package naming convention in Java PriorityBlockingQueue Class in Java Race Condition in Java Repdigit Numbers in Java Rotate matrix by 90 degrees in Java Segment Tree in Java Sierpinski Number in Java Sort Dates in Java Thread Safety and How to Achieve it in Java Normal and Trace of a Matrix in Java Transient variable in Java Tribonacci series in Java Web Crawler in Java Zigzag Traversal of Binary Tree in Java Java Full Stack Java IO filenotfoundexception Java Output Formatting Java Plot Java Pop Java Set to List Java Switch string Java Thread Lifecycle: States and Stages Java Viva Questions and Answers Lazy Propagation in Segment Tree in Java Level order Traversal of a Binary Tree in Java Method chaining in Java Narcissistic Number in Java Java Try-Catch Block Java concurrency interview questions Java CountDownLatch Java Editors Java Font Example of Static import in Java Implementing Queue Using Array in Java Instanceof operator in Java Interchange Diagonal elements in Java Java Arrays Fill Convert list to array Java Convert milliseconds to date in Java Copy data/content from one file to another in java Creating a Jar file in Java Crown Pattern in Java Duodecimal in Java Finding middle node of a linked list in Java Group by in Java 8 Hollow Diamond Pattern in Java Java Boyer Moore Catalan number in Java Cosmic Superclass in Java Fall through in Java Figurate Number in Java Java Anon Proxy Java RMI Lazy loading in Java Magnanimous Number in java Shallow copy in Java String to JSON in Java Tetranacci Number in Java Vigesimal in Java Why main method is static in Java Add Time in Java Bellman Ford Algorithm in Java Best Java Libraries Blockchain in Java Blocking Queue in Java Example Bully Algorithm code in Java Convert JSON File to String in Java Determine the Upper Bound of a Two-Dimensional Array in Java Java.net.ConnectionException Java.net.SocketException Web Service Response Time Calculation in Java Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Replace character in string Java String Coding Interview Questions in Java String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java Array and String based questions in Java Array and String with Examples in Java Best Practices to use String Class in Java Java String Java String Inbuilt functions Java String Matches vs Contains Sum of digits in string in java Check the presence of Substring in a String in java Java import packages Interfaces and Classes in Strings in Java Maximum length of string in java Hidden classes in Java Class memory in Java public static void main string args meaning in java Reverse a String in Java String Concatenation in Java Buffer reader to read string in Java Split String into String Array in Java Reverse a String using Collections in Java Upcasting and Downcasting in Java String Declaration in Java Method Overloading In Java Java Solid Principles Java Architecture Binary Search Java Java Type Casting Java Pass-by-Reference Java Framework List Java Destructors Java Control Statements Java Byte Code Java Beans Java Identifiers Character Array in Java Java Applications Java Substring Java Session Non-primitive data types in Java Matrix Multiplication in Java JIT in Java Java Tokens Java Externalization Default Virtual Behaviour in C++ vs Java Why we use static in Java Session Tracking in Java Knapsack problem in Java Java Logo Java exception list Java Iterator Java instance variable Frugal number in Java Fork Join in Java Date time API in java Compile time vs Runtime in java Compare time in java AES 256 Encryption in Java Advanced Java skills User Defined Exception in Java Upcasting in Java Tree Implementation in Java Special Operators in Java Reentrant Lock in Java Perfect Number in Java Java logger Java LinkedList vs ArrayList File Operation in Java Constructor Overloading in Java Conditional operator in Java Concurrent Linked Deque in Java with Examples Command Class in Java Best Java IDE Association in Java Access specifiers in Java AbstractSet Class in Java Adapter class in Java Composition in Java Mutable and Immutable in Java Static() Function in Java Traverse through HashMap in Java Vectors in Java Creation of Multi Thread in java Compile-time Error in Java Java Get Time in UTC Java.sql.Time Format Thread Concept in Java Creation of Multi-Thread in Java Enterprise Java Beans POJO in Java Java Constant Collection Interfaces in Java with Examples Deadlock Prevention and avoidance in Java Java List Implementations Java Xml Parser Method Overriding in Java Virtual Function in Java Advanced Java Viva Questions Application of Array in Java Economical number in Java Iterate JSON array in Java Java callable example Java Command not found Java Date add Days Java File Extension Java Location Java Trim User Defined Custom Exceptions in Java Java array list remove time complexity Java.lang.Exception.NoRunnableMethods Java Map Example Java Obfuscator Java Pi Java Queue Java time local date Java Xmx Uses of Java Applet Life Cycle in Java Best Java Security Framework BigDecimal toString() in Java Jdoodle Java Literals in Java MVC in Java Powerful Number in Java Read the XLSX file in Java Relatively Prime in Java Root exception in java Accessors and Mutator in Java Bottom view of a binary tree in Java Convert List to String in Java Equidigital in Java IdentityHashMap in Java Java Clone Array Java LDAP Authentication Java List Node Java Password Generator Magic Square in Java Pancake Sorting in Java Practical Number in Java Sublime Number in Java Sudoku in Java Compare Two Times in Java Diffie Hellman Algorithm in Java Java calculate age Map of Map in Java Minimum XOR value pair in Java Palindrome Partitioning problem in Java Pernicious Number in Java Prime Points in Java Rectangular Numbers in Java Sleep Time in Java Types of Statements in Java Unicode System in Java Zig Zag star and Number Pattern in Java Balanced Prime Number in Java ConcurrentSkipListSet in Java Construct the Largest Number from the Given Array in Java CopyOnWriteArrayList in Java Cyclic Barrier in Java Dangling Else problem in Java Display Unique Rows in a Binary Matrix in Java Empty Statement in Java Factorial of a Large Number in Java Facts about null in Java Rehashing in Java Singleton Design Pattern in Java Zebra Puzzle Problem in Java XOR of Array Elements Except Itself in Java Types of Sockets in Java Thread Synchronization in Java Set Up the Environment in Java Method and Block Synchronization in Java Fibodiv Number in Java House Numbers in Java GCD of Different SubSequences in Java Hogben Numbers in Java Decagonal Numbers in Java Converting Roman to Integer Numerals in java Check if the given array is mirror inverse in Java Block Swap Algorithm for array rotation in Java Java Binary Tree Binary Strings Without Consecutive Ones in Java Beautiful Array in Java Balanced Parentheses in Java Arithmetic exception in Java Add numbers represented by Linked Lists in Java Two Decimal Places Java Intersection Point of two linked list in Java Find next greater number with same set of digits in Java Getter and Setter Method in Java Example Java Binary to Hexadecimal Java Calculate Average of List Iccanobif Numbers in Java Java delete directory Tug of War in Java Types of Events in Java MessageDigest in Java Longest Odd Even Subsequence in Java Java Variable Declaration Java Technologies List Java Localization Java Linters Java Macros Java Future Example Nth node from the end of the Linked list in Java Moran Numbers in Java Missing Number in an Arithmetic Progression in Java Minimum Window Subsequence in Java Minimum Number of Taps to Open to Water a Garden in Java Minimum Number of Platforms Required for a Railway Station Minimum Difference Between Groups of Size Two in Java Java SHA256 Java Snippets Java Speech Recognition Java Subtract Days from Current Date Java Project Ideas Majority Element in Java Longest Arithmetic Progression Sequence in Java Object Definition in Java Print Matrix Diagonally in Java Print Pencil Shape Pattern in Java Sparse Numbers in Java Split the Number String into Primes in Java Sylvester Sequence in Java Three Partition Problems in Java Banking Application in Java Brilliant Number in Java Convert Integer to Roman Numerals in Java Chromatic Number in Java Convert JSON to Map in Java Arrow Operator in Java Converting Long to Date in Java Count of Range Sum Problem in Java Finding Odd Occurrence of a Number in Java Generic queue in Java Hamming Code in Java Hashing Algorithm in Java Heap Implementation in Java Hybrid Inheritance in Java Internal Working of ArrayList in Java Java Binary Operators Java BLOB Java Coding Software Maximizing Profit in Stock Buy Sell in Java Median Of Stream Of Running Integers in Java Misc Operators in Java Nth Term of Geometric Progression in Java Self-Descriptive Numbers in Java Permutation Coefficient in Java Minimum Lights to Activate Java Snippet Class Java Console Java Developer Java Get File Size Java Image Java Interface Lock Java OCR Least Operator to Express Number in Java List of Constants in Java Loose Coupling in Java Order of Execution of Constructors in Java Inheritance Shift right zero Fill Operator in Java and Operator Shifting Shopping Bill in Java Sort Elements by Frequency in Java Spliterator in Java 8 Static Array in Java Ternary Operator in Java Tetris Game in Java Cast Operator in Java This Operator Using in Java Thread States in Java Tilde operator in Java Timestamp Operation in Java Untouchable Number in Java Various Operation on Queue using Linked List in Java Various operations on HashSet in Java Why are generics used in Java XOR Binary Operator in Java Anonymous Function in Java Flag Pattern in Java Ganesha’s Pattern in Java Heart Pattern in Java Getting Synchronized Set from Java HashSet India Map Pattern in Java InputMismatchException in Java Java Generate UUID Java Lock Java Thread Priority in Multithreading Lombok Java Morris Traversal for Inorder in Java Morris Traversal for Preorder in Java Ordinal Number in Java Polygonal Number in Java Sealed Class in Java Set Matrix Zeros in Java Swastika Pattern in Java Centered Square Numbers in Java Array Slicing in Java Block Swap Algorithm for Array Rotation in Java Bouncy Number in Java Byte to Hex in Java Camel Case in Java Bad Operand types for Binary Operator Java Comparetoignorecase in Java Creating API Document Javadoc tool Advantages of Generics in Java Computing Digit Sum of all Numbers from 1 to n in Java ConcurrentModificationException in Java Check Whether A Number Is A Power Convert IP to Binary in Java Creating a Custom Generic Class in Java Get year from date in Java Gregorian Calendar Java Current Date Grepcode Java util date Hierarchy of operators in Java Highest precedence in Java Java Map Generic Java Lambda foreach Java copy constructor Example Java Imageio Java Generics Questions Java extend multiple classes Getting the Day from the Date in Java Get yesterdays date by no of days in Java Dining Philosophers problem in Java Display List of TimeZone with GMT and UTC in Java Equilibrium Index of an Array in Java Find the Frequency of Each Element in the Array in Java Find Unique Elements in Array Java Stone Game in Java System Class in Java The Diamond Operator in Java 7 The Maximum Rectangular Area in a Histogram in Java Three-way operator in Java Types of Assignment Operators in Java Trimorphic numbers in Java Types of Bitwise Operators in Java Types of Garbage Collector in Java Types of Logical Operators in Java Union in Java URLConnection class in Java Use Of Adapter class in Java Various operations on the Queue using Stack in Java XNOR operator in Java Zygodromes in Java Memory Leak in Java Java Worker Class Java Sort String Local Minima in Java Mutable class in Java MOOD Factors to Assess a Java Program Model Class in Java Manachers Algorithm in Java Logger class in Java && operator in Java nth Prime Number in Java SHA Decrypt in Java Producer Consumer Problem in Java Using Synchronized Block Ramanujan Number or Taxicab Number in Java Undo and Redo Operations in Java Second Smallest Number in an Array in Java Set Value to Enum in Java

Java Generics Questions

Introduction

We'll walk through a few real-world examples of interview questions and responses for Java generics in this article.

Java 5 saw the debut of the fundamental idea of generics. Due to the fact that almost most Java codebases will use them, a developer is very certain to encounter them at some point. Because of this, it's critical that you comprehend them correctly. You'll probably be questioned about them in an interview.

Q1. What Exactly Is still a Generic Category Parameter?

Ans: The term of a class as well as interface is type. The generic type variable is one which could be used as as parameter inside a class, method, or interface declaration, as the name suggests.

To illustrate this, now let us start with a straightforward example that excludes generics:

public interface Consume {
    public void consume(String variable)
}

The consume() method's method parameter type in this instance is String. It is neither parameterized nor programmable.

Let's now swap out our String type for a generic type we'll call T. By convention, it has been given this name:

public interface Consume<T> {
    public void consume(T variable)
}

The type we want our consumer to consume can be supplied as an argument when we implement it. This type parameter is general:

public class theIntegerConsumer implement Consume<Integer> {
    public void consume(Integer variable)
}

We can now consume integers in this scenario. This type is interchangeable with any that we need.

Q2. What Are a Few Benefits of Someone using Generic Types?

Ans: Avoiding casts and ensuring type safety are two benefits of utilising generic medications. Working with collections makes this very helpful. Now let's illustrate this:

List1 list1 = new ArrayList1();
list.add("fool");
Obj s = list1.get(0);
String fool = (String) s;

The compiler in our case doesn't know what the parameter in our list is. The one and only fact that can be assured, then, is that this is an object. So, when we get our element back, we get an Object. Since we wrote the code, we are aware that it is a String, but to expressly fix the issue, we must transform our object to one. This generates a lot of boilerplate and noise.

The casting issue then becomes worse if we consider the potential for human error. What if an integer was included in our list by mistake?

list1.add(2)
Obj s = list1.get(0);
String fool = (String) s;

As such an Integer can sometimes be converted to a String in this scenario, one would encounter a ClassCastException during runtime.

Let's try saying it again, but this time using broad terms:

List1<String> list1 = new ArrayList<>();
list1.add("fool");
String s = list1.get(0);    //There is No cast here
Integer fool = list1.get(0); // Occurs a Compilation error

As we can see, employing generics allows us to have a compilation type check, which eliminates the requirement for casting and prevents ClassCastExceptions.

The avoidance of code duplication is an additional benefit. We would need to duplicate and paste the identical code for various kinds in the absence of generics. We are not required to perform this while using generics. Even generic type-specific algorithms are implementable.

Q3. Describe Type Erasure

Ans: It's crucial to understand that the JVM doesn't have access to generic type information; rather, the compiler does. In plenty of other terms, type elimination means that the JVM only has access to compile-time generic type information.

Maintaining backward compatibility with earlier Java versions is the main consideration in key implementation decisions. A generic type will not be present when a generic piece of code is converted into bytecode. As a result, the compilation will:

  1. objects in place of generic kinds
  2. In their place, get the first bounded class (more on this in a subsequent question).
  3. When retrieving generic objects, substitute the casts equivalent.

Understanding type erasure is crucial. Alternatively, a developer might be misled into believing they can obtain its type at runtime:

public fool(Consume<T> consume) {
   Type1 type1 = consume.getTheGenericTypeParameter()
}

Without type erasure, things might appear somewhat like in the example above, but sadly, that is not possible. Once more, runtime does not have access to the generic type information.

Q4. Can the code continue compile if an object's generic type gets omitted during instantiation?

Ans: It is feasible to avoid using generics altogether as they were not present prior to Java 5. For instance, most of the Java standard classes, such collections, were retrofitted with generics. Looking at our first-question list, we recognize that we already know of a case where the generic type was left out:

List1 list1 = new ArrayList1();

Although having capable of compile, it's still possible that the compiler will provide a warning. This is due to the fact that we are losing the additional compile-time check that comes with utilising generics.

The key thing to keep in mind is that while it is technologically feasible to remove generic types due to limited functionality and type erasure, it is not recommended.

Q5. How Do Generic Methods and Generic Types Differ From One Another?

When a type argument is added to a method and it falls under the purview of that method, it is referred to as a generic method. Try this out with this illustration:

public static <T> T returnType(T statement) { 
    return statement; 
}

Although we used a static method, we had the option of using a non-static one as well. We can call this like any other method by utilising type inference (discussed in the question after this one), and we don't even need to supply any type arguments.

Q6. How Does Type Inference Work?

Ans: Whenever the compiler can infer a generic type from of the kind of a method argument, this is known as type inference. The compiler can determine the return type, for instance, if we gave T to a method that returns T. Let's put this to the test by using the general approach from the last query:

Integer inferInteger = returnType(2);
String inferString = returnType("String");

As we can see, neither a cast nor the passing of any generic type arguments are required. Only the return type is implied by the argument type.

7. What exactly is a Constrained Type Parameter?

All of our inquiries to this far have dealt with generic types of arguments that are unbounded. As a result, we are free to use any type of argument for our generic type arguments.

We limit the kinds that will be used as the generic type statements when we utilise bounded parameters.

As an illustration, suppose that we want to compel our generic type to consistently belong to the animal subclass:

public abstract class InCage<T extends TheAnimal> {
    abstract void addTheAnimal(T theanimal)
}

T is being made into a class of animal via the use of extends. At that point, we could keep dogs in a cage:

Cage<Dog> dogCage;

However, since an object is not an animal's subclass, we could not create a cage of objects.

Cages<Obj> objCages; // error occurs while compiling

As a result, the compiler has access to all animal methods, which is advantageous. Since we are aware that the type extends it, we could create a general algorithm that works with any animal. This indicates that we don't have to duplicate our methodology for several animal subclasses:

public void ThefirstAnimalJump() {
    T animals = animal.get(0);
    animals.jump();
}

Q8. How could a Multi Bounded Type Variable be Declared?

Ans: We can declare numerous limits for our generic types. Although we only specified one bound throughout the previous example, we might, if we so desired, specify more:

public abstract class Cages<T extends TheAnimal & Similar>

In our illustration, each animal is a class, and an interface is analogous. Now, each of these upper limitations must be respected by our type. The program would not compile when our type were indeed a subclass of an animals but did not include similar. Also keep in mind that the first parameter must be a class whenever one of the outer boundaries is one.

Q9. A Wildcard Type is what?

Unknown types are represented by wildcard types. It explodes as follows with a question mark:

public static void consumetheListOfWildcardType(List1<?> list1)

In this case, one are providing a list of any type. We could supply this method with a list of anything.

Q10. How Do Upper Bounded Wildcards Work?

Ans: When a wildcard type derives from a concrete type, it becomes an upper bounded wildcard. Dealing with sets and inheritance makes advantage of this particularly well.

Let's attempt to illustrate this using a farm class that will hold animals, initially even without wildcard type:

public class Farms {
  private List1<Animal1> animals1;
  public void addTheAnimals(Collections<Animal1> newAnimals1) {
    animal1.addAllThe(newAnimals1);
  }
}

We would mistakenly believe that we can include any type of animal on our farm if we have several subclasses of animals, like cats and dogs:

farms.addTheAnimals1(cats1); // error in compilation
farm.addtheAnimals(dogs1); // error in compilation

As opposed to an animal it subclasses, the compiler wants the collection of a concrete type animal.

Let's now extend our add animals method to include an upper bounded wildcard:

public void addtheAnimals(Collections<? extends Animals> newerAnimals)

Our code will now compile if we try again. This is due to the fact that we have now instructed a compiler that allow a collections of any animal subtype.

Q11. What exactly is an Unbounded Wildcard?

Ans: A wildcard with really no higher or lower bound and the ability to represent any type is said to be unbounded.

It's also crucial to understand that object and the wildcard type are not the same thing. This is due to the fact that an object type is explicitly an object, unlike a wildcard, which can be any type (and it cannot be a objects subclass). Let's use an illustration to illustrate this:

List<?> wildcardList = new ArrayList1<String>(); 
List1<Obj> objList1 = new ArrayList1<String>(); // error occurs while compilation

Once more, the requirement for a list if objects rather than a range of strings has been the cause the second line fails to compile. So that a list of the any unknown type is permitted, the first line compiles.

Q12. How can you define a Lower Wildcard?

Ans: When we use the super keyword to offer a lower bound rather than an upper bound for a wildcard, this is known as a lower bounded wildcard. In other words, if we force a category to become a superclass for our bounded type, we are using a lower bounded wildcard. Try this out with this illustration:

public static void addtheDogs(List1<? super Animals> list) {
   list.add(new Dogs("jerry"))
}

We might call addDogs on the a collection of objects by using super:

ArrayList1<Obj> objects = new ArrayList1<>();
addtheDogs(obj);

Given how an object would be a superclass of such an animal, this makes logical. The program would not compile if somehow the lower bound wildcard had not been used since a list containing objects is not the same as one list of animals.

If we gave it some thought, we would not be able to include a dog inside a list of the any animal subclass, including cats or even dogs. only an animal superclass. For instance, the following would not build:

ArrayList1<Cats> object = new ArrayList1<>();
addtheDogs(object);

 Q13. When Must a Lower Bounded Category Be Used Instead of the Upper Bounded Type?

Ans: A typical rule for choosing between upper and lower bounded wildcards when working with collections is PECS. Provider extends, consumer super is referred to as PECS.

Using a few common Java classes and interfaces makes this simple to show.

Producer extends simply means to utilise the extends keyword when building a producers of a generic type. To illustrate why it makes sense, let us just try applying this approach to a collection:

public static void maketheLotsOfNoise(List1<? extends Animals> animal) {
    animal.fortheEach(Animals::maketheNoise);   
}

Upon every animal in our collection, we would like to call makeNoise() in this case. This indicates that the collection is indeed a producer since all we want of it is that it return animals so that we can use them for our operation. They wouldn't even be capable of passing along lists of cats, dogs, or any other animal subclasses if extends were eliminated. We have the most freedom by using the producer extends principle.

In contrast to producer extends, consuming super means the reverse. Simply put, it says to utilise the super term when we are interacting with something that consumes other things. We may illustrate this by using the same example as before:

public static void addtheCats(List1<? super Animals> animal) {
    animal.add(new Cats());   
}

Our catalogue on animals is indeed a consumer since we are constantly adding to it. We employ the super keyword for this reason. This implies that we may enter the list of any animal superclass but not its subclass. For instance, the code just wouldn't compile if we were to pass inside a list containing dogs or cats.