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 How to run Java program in command prompt How to run Java program in Eclipse 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 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 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 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

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 Python vs Java 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 C vs 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 How to calculate time difference 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 String Tokenizer and Split Method in Java Difference Between BufferedReader and FileReader Difference Between Thread.start() and Thread.run()

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 create thread in Java How to find length of String 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 create custom exception in Java How to import packages in Java How to run applet Program in Java How to take Array Input in Java How to achieve abstraction 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

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 Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hiberate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial Jenkins java net socket connection time out

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

Misc

List all files in a Directory in Java Nonagonal number in Java Null Pointer Exception in Java Package naming convention in Java Packages Program in java Pangram Program in Java PriorityBlockingQueue Class in Java Race Condition in Java Repdigit Numbers in Java Reserved Keywords 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 program to print matrix in Z form 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 Case Keyword Java Try-Catch Block Java Class KeywordJava concurrency interview questions Java Continue Keyword Java CountDownLatch Java Default Keyword Java Double Keyword Java Editors Java Else Keyword Java Enum Keyword Java Extends keywordJava Finally Keyword Java Font Example of Static import in Java How Many Ways to Create Objects in Java Implementing Queue Using Array in Java Instanceof operator in Java Interchange Diagonal elements in Java Java Arrays Fill Java Char Keyword Convert list to array Java Convert milliseconds to date in Java Copy data/content from one file to another in java CRC Program in Java Creating a Jar file in Java Crown Pattern in Java Difference Between Access Specifiers and Modifiers in Java Difference Between Java and PHP Difference Between replace() and replaceall() in Java Duodecimal in Java Finding middle node of a linked list in Java Group by in Java 8 Hollow Diamond Pattern in Java How annotations work in Java Java Boyer Moore Catalan number in Java Cosmic Superclass in Java Difference between this and super 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 Contextual keywords 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 What are Array strings 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 What is String 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 How to stop execution after a certain time in Java 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 What is string in Java why it's immutable 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 Star Program in 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 What is advance Java? 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 Java Break Keyword 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 Java Enumeration Compile-time Error in Java Java Get Time in UTC Java.sql.Time Format Structure of Java Program Thread Concept in Java Creation of Multi-Thread in Java Enterprise Java Beans POJO in Java Volatile keyword in Java Java Constant Collection Interfaces in Java with Examples Deadlock Prevention and avoidance in Java Java Boolean Keyword Java Byte Keyword Java List Implementations Java Xml Parser Method Overriding in Java RMI program in Java Virtual Function in Java What is interpreter 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 What is anagram in Java? Accessors and Mutator in Java Bottom view of a binary tree in Java Convert List to String in Java Equidigital in Java How to check data type 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 How to Reduce Time Complexity 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 The final Keyword 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 Caesar Cipher Program 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 Java For Keyword Java Float Keyword Java Instanceof Keyword Java If Keyword Java Int Keyword Java Import Keyword Java Package Keyword Java Static 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 Tug of War in Java Types of Events in Java

How to create an array in Java

How to create an array in Java

An array is a linear data structure stores a collection of fixed number ofelements of similar type. The size of an array is specified when it is created. The array elements reside in the contiguous memory location.

For example, if we want to store the names of 200 employees, we can create a String type array instead of creating each variable of type String individually.

Some important things about the Java arrays are:

  • An array, once created, cannot be modified, i.e., the array size is fixed after the declaration, and the number of elements to be stored is fixed.
  • The size of an array must be an int or short value and not along.
  • We can declare an array like the other variables just with the square brackets ([]) after the datatype.
  • The array elements are stored in sequential order, and each element has an index starting with 0 (a[0], a[1], a[2], …..).
  • To find the length of an array in Java, we use the property called length.

For example,

intlen = array_name.length;
  • In Java, arrays are treated as an object and are dynamically allocated.
  • The Objectclass is the superclass of array type.
  • TheCloneableinterface and the Serializable interface are implemented by the array type.
  • In Java, an array can contain primitive types like int, char, float, etc., as well as the non-primitive types like an object. For primitive types, values are stored in a contiguous memory location, and for objects, the actual objects are stored in a heap segment.
  • Unlike C/C++, Java has the feature of anonymous arrays.

Advantages of an array in Java

  • The array elements can be accessed randomly using the array indexes.
  • Array elements are simple to retrieve and sort large data sets.

Disadvantages of an array in Java

  • Once an array is created, we cannot modify its size. Array size cannot be changed at runtime; therefore, it is called a static data structure.
  • An array cannot contain heterogeneous data; it can only contain data of a single primitive type at a time.

Types of arrays

There are two types of arrays in Java:

  1. One Dimensional array (1-D array):

It is also called a linear array or a single-dimensional array where the elements are stored in a single row.

Example:

intarr[] = new int[10];

  • Multidimensional array:

It is the combination of two or more arrays or the nested arrays. In the multidimensional array, more than two rows and columns can be used.

Multidimensional arrays can be two-dimensional (2D arrays) or three-dimensional (3D arrays), we will discuss more about 2D and 3D arrays in this tutorial.

Example:

int[][] arr = new [3][5];

OR

intarr[][] = {{1,2,3}, {4,5,6}, {7,8,9}};

One Dimensional Array in Java

How to create an array in Java

The above diagram showsa 1-D array of size 3. 1-D array or one dimensional array is a linear array where elements are stored sequentially in a row.

The syntax to declare a one-dimensional array is:

 data_typearray_name[]; OR
 data_type []array_name; OR
 data_type[] array_name; 

The data_type is the type of array elements like int, char, float,etc., or non-primitive type like object.

array_name is the name given to an array by the user.

The syntax to instantiate an array in Java:

Instantiating an array means to define the number of elements an array can hold.

array_name = new data_type[size];

Example:

 intarr[];
 arr = new int[20];
 //we can also combine the declaration and instantiation as
 intarr[] = new int[20]; 

Here, we have created a one dimensional array of integer type which can storemaximum 20 elements. In other words, size or length of the array is 20.

Note: To get an array is a two-step process. At first, we declare an array of a datatype and a name; then, we allocate the memory to hold the array, using a new operator, and assign it to the array variable we have created. And therefore, all the arrays in Java are dynamically allocated.

Initialization of arrays

In Java, the array elements can be initialized during the declaration.Thus, we can use the given way when the size and array elements are already known.

Example:

int[] roll_no = {101, 102, 105, 111, 130};

Here, roll_no is an array of type int which is initialized with the values given in curly braces.

For initialization, we haven't given the size of the array as the Java compiler itself specifies the size by counting the number of elements in that array. In our case, it is 5.

We don't need to write new int[] in the latest version of Java.

We can also initialize array elements using the indexes as shown below:

 //declaring the array
 int[] roll_no = new int[5];
 //initializing the array
 roll_no[0] = 101;
 roll_no[1] = 102;
 roll_no[2] = 105; 
..
How to create an array in Java

where, array values are stored as

  • Array index starts with 0, i.e., the first element of every array is at the index position 0.
  • If the array size is n, then the last element of an array is at the index n-1.

Accessing the array elements in Java

Using index numbers

An array can be accessed using its index. As discussed earlier, the index starts with

0 and ends at (size – 1) position.

The syntax to access array element using its index number:

array_name[index];

Let’s consider below example to access array elements using indexes:

ArrayUsingIndex.java

 public class ArrayUsingIndex{
           public static void main(String[] args) {
                    //declaring and initializing an array
                    int[] roll_no = {101, 103, 105, 100, 111};
                    //accessing array elements individually using index
                    System.out.println("Printing array elements using index:");
                    System.out.println("First element: " + roll_no[0]);
                    System.out.println("Second element: " + roll_no[1]);
                    System.out.println("Fifth element: " + roll_no[4]);
           }
 } 

Output:

How to create an array in Java

In the above example, we access the array elements using its indexes; however, we cannot access each element individually if the array size is large.Here, we can use loops to iterate through the array.

Using the loops

  1. Accessing an array using for loop:

Commonly, an array is iterated using the for loop in Java. It takes one counter variable (here it is i),which increments until it doesn't reach the end of an array (size – 1).

Syntax:

 for(initialization ; condition ; increment/decrement) {
 //body of the loop
 } 

Consider the following example to understand how to access the array using the fora loop.

ArrayUsingForLoop.java

 public class ArrayUsingForLoop{
           public static void main(String[] args) {
                    //declaring and initializing an array
                    int[] arr = {11, 34, 21, 77, 20, 2, 44, 78, 100, 66, 12, 30, 7};
                    //finding the length of array
                    intlen = arr.length;
                    //iterating through the array using for loop
                    System.out.println("\nPrinting array elements using for loop:");
                    for(inti = 0; i<len; i++) {
                              System.out.print(arr[i] + " ");
                    }
                    System.out.println();
           }
 } 

Output:

How to create an array in Java
  • Accessing an array using for-each loop:

The forEach loop was introduced in Java 5 commonly to iterate over an array or ArrayList. It prints the elements of an array, one by one. At first, it holds the elements in a variable (in our case, the variable is var) and then executes the body of the loop.

Syntax:

 for(data_typevariable_name : array_name) {
 //body of the loop
 } 

Consider following example for iterating array using for-each loop:

ArrayUsingForEach.java

 public class ArrayUsingForEach{
           public static void main(String[] args) {
                    //declaring and initializing an array
                    int[] arr = {11, 34, 21, 77, 20, 2, 44, 78, 100, 66, 12, 30, 7};
                    //finding the length of array
                    intlen = arr.length;
                    //iterating through the array using for-each loop
                    System.out.println("\nPrinting array elements using for-each loop:");
                    for(intvar : arr) {
                              System.out.print(var + " ");
                    }
                    System.out.println();
           }
 } 

Output:

How to create an array in Java

Arrays and Methods

  • Passing arrays to methods

We can pass arrays to the methods just like we pass variables and values of primitive type. For example, here we are passing an integer array to the method displayArray() as a parameter :

Example:

 public static void displayArray(int[] arr) {
           for(inti = 0 ; i<arr.length ; i++) {
                    System.out.print(arr[i] + " ");
 }
 } 

We can invoke this method by passing an array while calling it. Consider the example below:

intabc[] = { 2, 4, 22, 78, 21};

displayArray(array_name); // passing the array abc to the method

  • Returning array from method

A method can also return the array. Here the return type of the method is the same as that of the array with [].

Let's consider the below example to understand how to return an array from a method. Here, we are returning array rev, which is the reversal of actual array arr.

ReturnArray.java

 public class ReturnArray{
           //this method returns the reversed array
           public static int[] reverseArray(int[] arr, int size) {
           int rev[] = new int[size];
           int j = size;
           for(inti = 0; i< size; i++) {
                    rev[j-1] = arr[i];
                    j--;
           }
           return rev;
           }
           public static void main(String[] args) {
                    //creating the array
                    int[] roll = {2,4,6,8,10};
                    int n = roll.length;
                    inti;
                    System.out.println("Array before reversing");
                    for(i = 0; i< n; i++){
                              System.out.print(roll[i] + " ");
                    }
                    //calling the method and passing the array
                    //storing the fetched value in a new array
                    int[] result = reverseArray(roll, n);
                    //printing the fetched values
                    System.out.println("\nArray after reversing");
                    for(i = 0; i< n; i++){
                    System.out.print(result[i] + " ");
                    }
           }
 } 

Output:

How to create an array in Java

Arrays of Objects

In Java, the array of objects is used to store the objects of a class in an array. The array elements contain the location of reference variables of the object.

Syntax:

class_nameobject_name[] = new class_name[n];

where, n is the number of object references i.e. the array length

Let’s us consider below example to understand the array of objects:

ArrayOfObjects.java

 //creating class Student
 class Student{
           introll_no;
           String name;
           //constructor of class Student
           public void Student(int r, String str){
                    roll_no = r;
                    name = str;
           }
           public void displayData(){
                    System.out.print("Roll no =  " +roll_no+ " " + "Name of student = " +name);
                    System.out.println();
           }
 }
 public class ArrayOfObjects{
           public static void main(String[] args) {
                    //creating array of object of class Student
                    Student[] obj = new Student[3];
                    //creating and initializing the employee objects using constructor
                    obj[0] = new Student(101, "Nirnay");
                    obj[1] = new Student(102, "Rishi");
                    obj[2] = new Student(103, "Umang");
                    //display the Student object data
                    System.out.println("Student object 1:");
                    obj[0].displayData();
                    System.out.println("Student object 2:");
                    obj[1].displayData();
                    System.out.println("Student object 3:");
                    obj[2].displayData();
           }
 } 

Output:

How to create an array in Java

Array exceptions

  1. ArrayIndexOutOfBoundsException

During the traversal, if the size of an array is negative, or equal to the size of the array or greater than the size of an array, the Java Virtual Machine (JVM) throws ArrayIndexOutOfBoundsException.

It is a runtime exception that is the compiler doesn't check for this error during the compilation.

  • NullPointerException

It is also a runtime exception. Following conditions generate the NullPointerException in Java. It is thrown when the application uses null if there is a requirement of an object.

  • When the instance method of null object is called
  • The field of the null object is accessed or modified.
  • Taking the length of null as if it is an array.
  • When null is thrown as if it is a Throwable value.
  • When the null slots are accessed and modified like an array.

3.  NegativeArraySizeException 

It is thrown when the array we attempt to create an array of negative length. The NegativeArraySizeException extends the RuntimeException class in Java.

4.  IndexOutOfBoundsException

All the indexing pattern data types like array, vector, etc., throw IndexOutOfBoundsexception if they accessed out of their indices (range). This class also extends RuntimeException class.

5.  ClassCastException

This exception is thrown when a Java program attempts to cast an object to a subclass that is not its parent class. It is a separate class that extends the class RuntimeException.

6.  ArrayStoreException

This exception is thrown when a Java program attempts to store the wrong type of object in the array of objects. It is also a separate class that extends the class RuntimeException.

Example:

 Object arr[] = new String[10];
 arr[0] = new Double(0); 

in the above example, ArrayStoreException is thrown as it tries to store Double object into a String array of objects.

Let’s see the following example to understand the different types of exceptions in array:

ArrayExceptions.java

 public class ArrayExceptions{
           public static void main(String[] args) {
                    intarr[] = null;
                    int size = 5;
                    intincrementArr = -0;
                    int result;
                    for(inti = 0; i< 7 ; i++){
                              try{
                                       switch(i){
                                                 //gives a NullPointerException
                                                 case 0: result = arr[0];
                                                 break;
                                                 //gives a NegativeArraySizeException
                                                 case 1:
                                                 arr = new int[incrementArr];
                                                 result = arr[incrementArr];
                                                 break;
                                                 //gives aArrayIndexOutOfBoundsException
                                                 case 2:
                                                 arr = new int[size];
                                                 result = arr[size];
                                                 break;
                                                 //gives aIndexOutOfBoundsException
                                                 case 3:
                                                 arr = new int[6];
                                                 result = arr[6];
                                                 //gives a ClassCastException
                                                 case 4:
                                                 Object new_arr = new Integer(0);
                                                 System.out.println((String) new_arr);
                                                 //gives aArrayStoreException
                                                 Object obj_arr[] = new String[-5];
                                                 obj_arr[0] = new Integer(0);
                                                 System.out.println(obj_arr);
                                       }
                              }
                              catch (NullPointerException exception1){
                                       System.out.println("Exception is a: " +exception1.getMessage());
                                       exception1.printStackTrace();
                              }
                              catch (NegativeArraySizeException exception2){
                                       System.out.println("Exception is a: " +exception2.getMessage());
                                       exception2.printStackTrace();
                              }
                              catch (ArrayIndexOutOfBoundsException exception3){
                                       System.out.println("Exception is a: " +exception3.getMessage());
                                       exception3.printStackTrace();
                              }
                              catch (IndexOutOfBoundsException exception4){
                                       System.out.println("Exception is a: " +exception4.getMessage());
                                       exception4.printStackTrace();
                              }
                              catch (ClassCastException exception5){
                                       System.out.println("Exception is a: " +exception5.getMessage());
                                       exception5.printStackTrace();
                              }
                              catch (ArrayStoreException exception6){
                                       System.out.println("Exception is a: " +exception6.getMessage());
                                       exception6.printStackTrace();
                              }
                    }
           }
 } 

Output:

How to create an array in Java

Change the array element

We can change the value of a specific element, even if the array is already initialized with the help of an index number.

For example:

city[1] = "Jaipur";

Let’s consider following example. Here we are changing the value of index position 1 from "Delhi" to "Jaipur"

ElementChange.java

 public class ElementChange{
           public static void main(String[] args) {
                    String city[] = {"Mumbai", "Delhi", "Hyderabad", "Kolkata"};
                    city[1] = "Jaipur";
                    //printing the array after element changed
                    for(inti = 0; i<city.length; i++)
                    System.out.println(city[i]);
           }
 } 

Output:

How to create an array in Java

Multidimensional array in Java

It is a type of array which contains one or more arrays. In other words, a multidimensional array can hold multiple rows and columns.

The syntax of a multidimensional array is as follows:

data_type [dimension 1][dimension 2][]...[dimension N] array_name = newdata_type[size 1][size 2]…[size N];

where,

data_type: It is the type of array elements like int, string, float, etc.

dimension: It is the dimension of array like 1D, 2D, etc.

array_name: It is the name of the array.

size: It is the size of the dimension.

Types of Multidimensional Array:

Commonly used multidimensional array in Java is:

  • Two-dimensional array (2-D array)
  • Three-dimensional array (3-D array)

Calculating the size

To calculate the size of multidimensional arrays, i.e., its total number of elements, we can multiply the size of all dimensions.

  • Ifwe declare a 2-D array as:
int[][] arr = new int[5][3];

It will store (5*3) = 15 elements in total.

  • And if the array is a 3D array
int[][][] arr = new int[5][7][8];

It will store (5*7*8) = 280 elements.

  1. Two Dimensional Array:

2D array stores n number of rows and m number of columns. It can be called an array of array (1D array). It is mainly used for games like Super Mario for displaying the screen, displaying spreadsheets, etc.

How to create an array in Java

The syntax to declare a 2-D array is:

data_type[][] array_name = new data_type[r][c];          

where, r is the number of rows and c is the number of columns in the array.

Example:

char[][] arr = new char[5][7];

The syntaxto initialize a 2-D array:

array_name[row_index][column_index] = value;

Example:

arr[1][3] = 45;

We can also declare and initialize the array directly as:

          data_type[][] array_name = { {valueRow1Column1, valueRow1Column2,…}, {valueRow2Column1, valueRow2Column2,….} };

Example:

int[][] arr = { {11, 12}, {21, 22} };

Accessing the elements of 2D array

The element of a 2D array can be depicted as arr[i][j] where i is the number of rows and j is the number of columns.

Syntax:

arr[row_index][column_index];

If we declare an array as

int[][] arr = new int[2][3];

then we can access its elements directly as

arr[0][1] = 44;

which is the array element located at 1st row and 2nd column.

Let’s consider this example to understand how to create and print the 2-D array. We are creating two matrices and adding them. To display and operate over the elements of two-dimensional array, we use nested for loops i.e., a for loop within another for loop (one is to traverse the rows and another is to traverse the columns).

TwoDimensionalArray.java

 public class TwoDimensionalArray{
           public static void main(String[] args) {
                    int[][] arr1 = {{1, 2}, {3, 4}};
                    int[][] arr2 = {{10, 20}, {30, 40}};
                    int[][] arrSum = new int[2][2];
                    inti,j;
                    System.out.println("Matrix array 1:");
                    for(i = 0; i< 2; i++){
                              for(j = 0; j < 2; j++){
                                       System.out.print(arr1[i][j] + " ");
                              }
                              System.out.println();
                    }
                    System.out.println("Matrix array 2:");
                    for(i = 0; i< 2; i++){
                              for(j = 0; j < 2; j++){
                                       System.out.print(arr2[i][j] + " ");
                              }
                              System.out.println();
                    }
                    //Adding two matrix arrays
                    for(i = 0; i< 2; i++){
                              for(j = 0; j < 2; j++){
                                       arrSum[i][j] = arr1[i][j] + arr2[i][j];
                              }
                    }
                    System.out.println("Sum of matrix array:");
                    for(i = 0; i< 2; i++){
                              for(j = 0; j < 2; j++){
                                       System.out.print(arrSum[i][j] + " ");
                              }
                              System.out.println();
                    }
           }
 } 

Output:

How to create an array in Java
  • Three Dimensional Array
How to create an array in Java

Unlike a 2D array, a 3D array is complex and rarely used in real-time applications. In simpler words, it can be called an array of 2-D array.

The syntax to declare a 3D array is:

data_type[][][] array_name = new data_type[i][r][c];    

Example:

int[][][] arr = new int[10][12][15];

The syntax to initialize the 3D array is:

array_name[array_index][row_index][column_index] = value;

Example:

arr[2][3][1] = 34;

We can also declare and initialize 3D array together as:

 data_type[][][] array_name = { {
 { valueArray1Row1Column1, valueArray1Row1Column2,…},
 { valueArray1Row2Column1, valueArray1Row2Column2, ….}},
 {
 { valueArray2Row1Column1, valueArray2Row1Column2,…},
 { valueArray2Row2Column1, valueArray2Row2Column2, ….}}
 }; 

Example:

int[][][] arr = { {{1, 2}, {3, 4}}, {{5, 6}, {7, 8}} };

Accessing the elements of 3D array

The element of a 3D array can be depicted as arr[i][j][k], where i is the number of arrays, j is the number of rows and k is the number of columns.

Syntax:

arr[array_index][row_index][column_index];

If we declare an array as

int[][][]arr = new int[2][3][5];

then we can access its elements directly as

arr[0][1][2] = 44;

which is the element located at second row and third column of the first array of a 3D array.

Consider the following example to understand how to create and display a 3D array. Like the 2D array, we need to use nested loops for displaying and operating over a 3D array. However, we use three for loops in the case of the 3D array, one for traversing the arrays, the second for the rows, and the third for the columns.

ThreeDimensionalArray.java

 public class ThreeDimensionalArray{
           public static void main(String[] args) {
                    //initializing a 3D array containing 3 arrays
                    //with two rows and 3 columns
                    int[][][] arr = {{{1, 2, 3}, {3, 4, 7}},
                                                 {{10, 20, 30}, {50, 60, 70}},
                                                 {{100, 200, 500}, {300, 400, 800}}};
                    inti, j, k;
                    System.out.println("Displaying the 3D array:");
                    for(i = 0; i< 3; i++){
                              for(j = 0; j < 2; j++){
                                       for(k = 0; k < 3; k++){
                                                 System.out.print(arr[i][j][k] + " ");
                                       }
                                       System.out.println();
                              }
                              System.out.println();
                    }       
           }
 } 

Output:

How to create an array in Java

Jagged Array in Java

It is a special type of multidimensional array in Java, where the number of row elements varies. In other words, a jagged array is a 2D array with an odd number of columns.

Consider the below example to understand how to create a jagged array.

JaggedArray.java

 public class JaggedArray{
           public static void main(String[] args) {
                    //declaring a 2D array
                    int[][] arr = new int[3][];
                    //instantiating first row of the array with 4 columns
                    arr[0] = new int [4];
                    //instantiating second row of the array with 2 columns
                    arr[1] = new int[2];
                    //instantiating third row of the array with 3 columns
                    arr[2] = new int[3];
                    int count = 0;
                    //initializing the jagged array
                    for(inti = 0; i<arr.length; i++){
                              for(int j = 0; j <arr[i].length; j++){
                                       arr[i][j] = count++;
                              }
                    }
                    //printing the array
                    for(inti = 0; i<arr.length; i++){
                              for(int j = 0; j <arr[i].length; j++){
                                       System.out.print(arr[i][j] + " ");
                              }
                              System.out.println();
                    }
           }
 } 

Output:

How to create an array in Java

In this way, we have learned how to create different types of arrays in Java.



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