Java Programming Complete Tutorial

The Java Programming Language is a general-purpose, high-level, strongly-typed, class-based object-oriented programming language. All Java applications first complied with the bytecode that can run on any Java Virtual Machine (JVM) regardless of the underlying computer architecture. 

 

Introduction to Programming:

• What is Computer Programming?
• Where can I write my code?

Basic of Java:

• Introduction to Java Programming.
• Introduction to Flowchart and Pseudocode.
• Data Types in Java.
• Type Casting in Java.
• Operators in Java. 
• Read Input from User in Java.
• Decision-Making Statement in Java. 
• if...else statement in Java.
• Switch case statement in Java. 
• For loop in Java. 
• While loop in Java. 
• Do While loop in Java. 

Java Classes and Objects.

• Java Classes and Objects.
• Access Specifiers in Java. 
• Accessors and Mutators in Java. 

Array in Java. 

• Array Data Structure in Java. 
• Linear Search in Java.
• Binary Search in Java.

Access Specifiers in Java.

The process of hiding information is implemented using Access Specifiers known as visibility modifiers. They regulate access to classes, fields, and methods. Access Specifiers specify if fields or methods in a class can be invoked from another class or sub-class. In simple words, they are used to restrict access. 

There are four types of Access Specifiers in Java. 

• Public
• Private
• Protected
• Default (no specifier)

Public: Classes, methods, and fields declared as public can be accessed from any class in an application. 

Default: If Classes, variables, and methods have a default specifier we can access them only within the same package but not from outside this package. 

When no access specifiers are specified for an element, its accessibility level is the default. There is no keyword default. (alert-passed)

Private: Private methods and fields can only be accessed within the same class to which the methods and field belong. 

Protected: Protected methods and fields are accessible within the package and outside the package but with the help of inheritance. It cannot be applied to a class and it provides more accessibility than the default access specifier.    

Access Modifiers	default	private	protected	public
Accessible inside the class	Yes	Yes	Yes	Yes
Accessible within the subclass inside the same package	Yes	No	Yes	Yes
Accessible outside the package	No	No	No	Yes
Accessible within the subclass outside the package	No	No	Yes	Yes

Accessors and Mutators in Java.

Accessors and Mutators are two very important concepts in Java. It is used to read and update the private data member of a class. 

To understand this concept more clearly we first have to understand encapsulation and access specifiers. Encapsulation is an important concept in Object-oriented programming and it is implemented by wrapping up the data and methods into a single unit. 

The data present inside the class need to be secure and for this, we declare the data in a class as private. We cannot access the private data-member of other classes outside that class. To read and update the private data member a class outside that class we have to use public methods of that class. These methods are called Accessors or Getters and Mutators or Setters. 

Accessor or Getters are methods used to return the value of a private field of a class. It does not change the state of the Object. 

example:

public String getName() {
    return name; 
}    

Mutators or Setters are methods used to set a value of a private field of a class. It changes the state of the object. 

example:

public void setName(String fullName) {
    name = fullName;
}    

Example Java Program to Understand Accessors and Mutators.

public class Student {
    
    //attribute
    private int studId;
    private String studName;
    
    //Accessors or Getters
    public int getStudId() {
        return studId;
    }
    public String getStudName() {
        return studName;
    }
    //Mutators or Setters
    public void setStudId(int studId) {
        this.studId = studId;
    }
    public void setStudName(String studName) {
        this.studName = studName;
    }
}

import java.util.*;

public class Main
{
	public static void main(String[] args) {
	    //Object Creation
	    Student Obj = new Student();
	    
	    //assign value using Setters
	    Obj.setStudId(112);
	    Obj.setStudName("Rahul");
	    
	    //retrive value using Getters
	    System.out.println("Student ID: "+Obj.getStudId());
	    System.out.println("Student Name: "+Obj.getStudName());
	}
}

Output:

Student ID: 112
Student Name: Rahul

In the above example, we can see that how we are reading and updating the private data member of the Student class from the Main class with the help of the Object of Student class. 

Hope you found this article useful if you have any question related to this topic feel free to ask me in the comment section below. 

Java Classes and Objects.

Java is an Object-Oriented Programming Language and writing a program in Java is totally different from any other Object-Oriented Programming Language like C++ or Python. In Java, it is necessary to create a class before writing any solution to any programming question. 

Why it is important to create a Class in Java?

The property of the class is to combine all the properties and behaviors of an object in a program into a single unit.  A class is a template or blueprint that describes the behavior/states that an object of its type supports. 

What is an Object?

Any real-world entity with well-defined properties is called an Object. An Object will have a state, behaviors, and unique identity. An object can be tangible (physical entity) or intangible (cannot be touch or feel). 

There are three main characteristics of Objects, 

• State: Represents the data of an object. 
• Behavior: Represents the behavior of an object such as deposit, withdrawal, etc. 
• Identity: It is used internally by the JVM to identify each object uniquely. 

What is a Class?

A class defines its object properties and object behavior through methods. A class is a template for a collection of objects that share a common set of attributes and behavior. In the perspective of Object-Oriented programming, a class is a description of the object. It describes the data that each object possesses and it also describes the various behaviors of the object. 

In the above example, you can see a class name Car and with its three different objects Car1, Car2, and Car3 having their own behavior and identity. 

Example of class:
public class Car {
   String carColor;
   String carBrand;
   String fuelType;
}

Example of object:
Car objCar = new Car();

Attribute Declaration. 

Attributes / Fields are used to declare the properties of a class. These attributes are called instance variables. They can be intrinsic types like int, boolean, etc, or user-defined types. 

example: private double salary;

Method Declaration. 

Methods describe the responsibility of the class. These methods are common for all objects. Hence they are known as instance methods. A method always has a name and a return type and it can accept parameters. 

example:
public void calculateArea(int height) {
     int result = height*height;
  System.out.println(result);
}  

Read Input From User in Java.

In Java, Input can be read from the keyboard in many ways. One such way is to use the predefined/inbuilt class Scanner which is present in java.util package. Predefined/inbuilt classes in Java are organized in the form of packages. To use Scanner class, include package java.util using import statement as:

//import just a Scanner class
import java.util.Scanner;

//import the entire package java.util
import java.util.*;

Next, create a Scanner object to give input from the system from the given keyboard.

• Scanner sc = new Scanner(System.in);

import java.util.Scanner;

public class Main
{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter Roll No: ");
		int rollNo = sc.nextInt(); //integer input
		
		System.out.println("Enter Student name: ");
		String name = sc.next();  //single word input
		
		System.out.println(rollNo+" : "+name);
	}
}

Output:

Enter Roll No:
112
Enter Student name:
John
112 : John

Like in the above example, the Scanner class has methods to get input of various data types. 

Methods	Data Type
nextInt()	Integer
nextFloat()	Float
nextDouble()	Double
nextLong()	Short
nextBoolean()	Boolean
next()	Single word (String without space)
nextLine()	String without space
* For next() :even if you try to input multiple words, the will takes the first word only as input

Important note: Reading String using nextLine().

Scanner sc = new Scanner(System.in);

System.out.println("Enter the Student name: ");
String name = sc.next();

System.out.println("Enter the Address: ");
String address = sc.nextLine();

System.out.println("Name: "+name+" Address: "+address);

When you will execute the above code, the address will not be taken as input because Scanner skips the nextLine() when it is used after the next() or nextXxx() (ex: nextInt()) method. It is because the next() reads only the String, not the new line, and nextLine() consumes the next line (\n) as input, hence no input is received. 

To overcome this problem, when using nextLine() after next() or nextXxx(), consume the new line by including the statement sc.nextLine(). See the below example to understand more. 

import java.util.Scanner;

public class Main
{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter Roll No: ");
		int rollNo = sc.nextInt();
		
		//captures the new line 
		sc.nextLine(); 
		System.out.println("Enter Student Full Name: ");
		String name = sc.nextLine();
		
		System.out.println(rollNo+" : "+name);
	}
}

Output:

Enter Roll No: 
112
Enter Student Full Name: 
John Gupta
112 : John Gupta

Binary Search Algorithm in Java.

Given a sorted integer array arr[] of size n and a target element X, the task is to write a Java program to find and return the index of the target from the given array. Return -1 if the target element is not present in the array.

Example:

Input: arr[] = {1, 2, 3, 4, 5, 6, 8} X = 4
Output: Element found at index 3

Input: arr[] = {3, 5, 10, 11, 12} x = 6
Output: Element not found in the array

Binary search and Linear search are the two most popular search algorithms and binary search is more efficient because its time complexity is less than linear search. But the important thing to note is that binary search is only applicable to a sorted array. 

Binary Search Algorithm.

The Binary Search Algorithm is based on the idea of comparing the target value with the middle element of the array. If the target value is equal to the middle value of the array then searching is complete. If they are not equal and the target value is smaller than the middle value, we will continue searching on the left side of the array. If the target value is larger than the middle value, we will continue searching on the right side of the array. 

Steps for Binary Search Algorithm:

• Initialize the left and right pointer as low = 0, high = n-1. 

• While low <= high, compare the middle element arr[mid] of the array with target value x. 

• If the middle element matches with target arr[mid] = x, return the index of the middle element mid.

• If the target is less than the middle element arr[mid] > x, continue searching the left half. (high = mid - 1)

• If the target is larger than the middle element arr[mid] < x, continue searching the right half. (low = mid + 1)

• If the target element is not found, return -1.

Java Program for Binary Search Using Iteration.

// Java code to search the target element using binary search
public class BinarySearch {

    public static int binarySearch(int[] arr, int target) {
        int left = 0, right = arr.length - 1;

        while (left <= right) {
            int mid = left + (right - left) / 2;

            if (arr[mid] == target) {
                return mid;
            } else if (arr[mid] < target) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }

        return -1; // Element not found
    }

    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        int target = 5;

        int result = binarySearch(arr, target);

        if (result != -1) {
            System.out.println("Element found at index " + result);
        } else {
            System.out.println("Element not found in the array");
        }
    }
}

Output:

Element found at index 4

Time Complexity: Binary search has a time complexity of O(log n), where n is the number of elements in the array. This is because, with each comparison, the size of the remaining array is halved.

Space Complexity: Binary search has a space complexity of O(1). It doesn't require additional memory that scales with the size of the input.

Java Program for Binary Search Using Recursion.

// Java code for Binary Search to target element using Recursion
public class BinarySearch {

    public static int binarySearchRecursive(int[] arr, int target, int left, int right) {
        if (left <= right) {
            int mid = left + (right - left) / 2;

            if (arr[mid] == target) {
                return mid;
            } else if (arr[mid] < target) {
                return binarySearchRecursive(arr, target, mid + 1, right);
            } else {
                return binarySearchRecursive(arr, target, left, mid - 1);
            }
        }

        return -1; // Element not found
    }

    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        int target = 5;

        int result = binarySearchRecursive(arr, target, 0, arr.length - 1);

        if (result != -1) {
            System.out.println("Element found at index " + result);
        } else {
            System.out.println("Element not found in the array");
        }
    }
}

Output:

Element found at index 4

Time Complexity: O(log n) where n is the size of the given array. 

Space Complexity: O(log n) because extra stack space is required to perform Recursion.

Java Program for Binary Search Using Built-in Function.

In Java, you can use the Arrays.binarySearch() method to perform a binary search on an array. This method is part of the java.util package and is designed to work with arrays that are already sorted.

Java Code:

// Binary Search Built-in Function in Java to search 
// an element in sorted array
import java.util.Arrays;

public class BinarySearch {

    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
        int target = 6;

        // Sorting the array (required for binary search)
        Arrays.sort(arr);

        // Using binarySearch method
        int result = Arrays.binarySearch(arr, target);

        if (result >= 0) {
            System.out.println("Element found at index " + result);
        } else {
            System.out.println("Element not found in the array");
        }
    }
}

Output:

Element found at index 5

Time Complexity: The Arrays.binarySearch() method has a time complexity of O(log n), similar to a standard binary search algorithm.

Space Complexity: The Arrays.binarySearch() method has a space complexity of O(1). It doesn't require additional memory that scales with the size of the input.

Linear Search Algorithm in Java.

Given an integer array of size n and a target element X, the task is to write a Java program to search and return the index of the target element from the given array. Return -1 if the target element is not present in the given array.

Example:

Input: arr[] = {9, 1, 3, 5, 7}  X = 3
Output: Element found at index 2

Input: arr[] = {1, 2, 3, 4, 5, 7, 9}  X = 6
Output: Element not found in the array

This problem can be easily solved by using any search algorithm. In Java, we have two searching algorithms Linear Search and Binary Search, and in this article, we will understand the workings of Linear Search Algorithm and how to use it to find a target element in the given array.

Linear Search Algorithm.

Linear search is a simple searching algorithm that finds the position of a target value within a list. It sequentially checks each element of the list until a match is found or the entire list has been searched.

Step-by-step Algorithm:

Step 1: Start from the first element of the array.

Step 2: Compare the target value with the current element:

• If it matches, return the index.
• If it doesn't match, move to the next element.

Step 3: Repeat step 2 until a match is found or the end of the array is reached.

Step 4: If the end of the array is reached and no match is found, return -1 to indicate that the element is not present in the array.

Pseudo Code for Linear Search Algorithm.

function linearSearch(arr, target):
    for i from 0 to length of arr - 1:
        if arr[i] equals target:
            return i
    return -1

Java Program for Linear Search Algorithm.

// Java code for linear search algorithm to find and
// return the index of searching element
public class LinearSearch {

    public static int linearSearch(int[] arr, int target) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == target) {
                return i;
            }
        }
        return -1;
    }

    public static void main(String[] args) {
        int[] arr = {4, 2, 7, 1, 9, 5};
        int target = 7;

        int result = linearSearch(arr, target);

        if (result != -1) {
            System.out.println("Element found at index " + result);
        } else {
            System.out.println("Element not found in the array");
        }
    }
}

Output:

Element found at index 2

• Time Complexity: In the worst case, linear search has a time complexity of O(n), where n is the number of elements in the array. This is because, in the worst scenario, we may have to go through the entire array to find the element.

• Space Complexity: Linear search has a constant space complexity of O(1). It doesn't require additional memory that scales with the size of the input.

Linear search is straightforward and effective for small datasets or unordered lists. However, for large datasets or lists where the elements are sorted, more efficient algorithms like binary search are preferred.

Arrays Data Structure in Java.

An Array is a reference data type that can hold a fixed number of the same type of data. Array elements are store contiguously and the length of the array is decided when the array is created. We cannot change the array length after creation. 

Array in Java is very different than the array present in other programming languages like C/C++. Some key points to note about Array in Java. 

• In Java, arrays are dynamically allocated. What does it mean? It means that we can allocate memory to an array at run time using the heap. 
• Arrays are objects in Java and we can use several array properties on them like we can use object property length to know the size of the array. 
• We can specify the size of the array using int and short data type only. 

An array in Java can hold primitive data like int, char, long, etc, and non-primitive data types like object references. 

int mark[] = {10, 20, 30, 40 ,50}; //primitive datatype

Employee empList[] = new Employee[3]; //non-primitive datatype

empList[0] = new Employee();
empList[1] = new Employee();
empList[2] = new Employee();

The values that we store in an array are called elements and each element can be accessed by using their index. 

Declaring an Array in Java. 

The two common ways of declaring an array in Java is:

datatype[] arrayName;
        or
datatype arrayName[];

//You can declare array of several different datatype:
int[] arrayInt;
long[] arrayLong;
short[] arrayShort;
float[] arrayFloat;
double[] arrayDouble;
boolean[] arrayBoolean;
char[] arrayChar;
String[] arrayString;

Creating an Array in Java.

An array is created when we allocate memory to an array. 

arrayInt = new int[10]; //creating an array

Initializing an Array in Java.

It is a process of assigning values to each element of the array. 

arrayInt[0] = 10;   //initializing first element
arrayInt[1] = 15;   //initializing second element
arrayInt[2] = 20;   //initializing third element
arrayInt[3] = 25;   //so on..
arrayInt[4] = 30;

Accessing Array Elements in Java. 

We can access any array elements using their index value.

System.out.println(arrayInt[0]); //15
System.out.println(arrayInt[1]); //20
System.out.println(arrayInt[4]); //30

System.out.println(arrayInt[8]); //0
because our array length is 10 but the index 8 is not initialize with any value so by default it assign with 0. 

System.out.println(arrayInt[11]); //Error
We will get "ArrayIndexOutOfBoundsException" because our array length is 10 and we are trying to access index value 11 which is out of its range.

Java program to create integer array and access each element using their index value.  

public class ArrayExample
{
	public static void main(String[] args) {
		//declare an integer 
		int[] array;
		
		//allocating memory to the array 
		array = new int[8];
		
		array[0] = 10;  //initializing first element
		array[1] = 20;  //initializing second element
		array[2] = 30;
		array[3] = 40;
		System.out.println("Element at index 0: "+array[0]); //accessing first element
		System.out.println("Element at index 1: "+array[1]); //accessing second element
		System.out.println("Element at index 2: "+array[2]);
		System.out.println("Element at index 3: "+array[3]);
		System.out.println("Element at index 6: "+array[6]);
	}
}

Output:

Element at index 0: 10
Element at index 1: 20
Element at index 2: 30
Element at index 3: 40
Element at index 6: 0

You can also access array elements using a loop.

public class Main
{
	public static void main(String[] args) {
		//declare an integer 
		int[] array;
		
		//allocating memory to the array 
		array = new int[5];
		
		array[0] = 10;  //initializing first element
		array[1] = 20;  //initializing second element
		array[2] = 30;
		array[3] = 40;
		array[4] = 50;
		
        System.out.println("Length of Array: "+array.length);  
        
		for(int i = 0; i < array.length; i++) {
		    System.out.println("Element at index "+i+":"+array[i]);
		}
	}
}

Output:

Length of Array: 5
Element at index 0:10
Element at index 1:20
Element at index 2:30
Element at index 3:40
Element at index 4:50

An array of Objects. 

An array can also store objects similarly like it stores primitive data types. 

Example:
Student studentList[] = new Student[3];

The array variable studentList[] does not hold an array of Student objects, instead, it holds an array of Student reference variables. To make these variables hold the object, we have to create the object as:

studentList[0] = new Student();
studentList[1] = new Student();
studentList[2] = new Student();

Example of Array of Object in Java.

import java.util.*;

class Student {
    public int stud_roll_no;
    public String studen_Name;
    Student(int rollno, String name) {
        this.stud_roll_no = rollno;
        this.studen_Name = name;
    }
}

public class Main
{
	public static void main(String[] args) {
	    Scanner sc = new Scanner(System.in);
	    
	    //allocating memory to object of type student
		Student studentList[] = new Student[3];
		
		//initializing elements of the array
		for(int i = 0; i < studentList.length; i++) {
		    System.out.println("Enter the rollNo: ");
		    int rollno = sc.nextInt();
		    
		    System.out.println("Enter the name: ");
		    String name = sc.next();
		    
		    studentList[i] = new Student(rollno, name);
		}
		
		//accessing elements of the array 
		for(int i = 0; i < studentList.length; i++) {
		    System.out.println(studentList[i].studen_Name+" Roll no is: "+studentList[i].stud_roll_no);
		}
	}
}

Output:

Enter the rollNo: 
101
Enter the name: 
Rahul
Enter the rollNo: 
102
Enter the name: 
Mohit
Enter the rollNo: 
103
Enter the name: 
Kajal
Rahul Roll no is: 101
Mohit Roll no is: 102
Kajal Roll no is: 103

Multidimensional Arrays in Java.

A multidimensional array is also called an Array of Arrays in which an array holds another array. Each row of the array can contain different lengths. The dimension of the array is decided by the number of square brackets ([ ]) you are adding. These are also known as Jagged Array. 

• int[] arr; // 1D array
• int[][] arr; // 2D array
• int[][][] arr; //3D array  

Example to 2D Array in Java.

public class Main
{
	public static void main(String[] args) {
		
		int[][] arr = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
		
		for(int i = 0; i < 3; i++) {
		    for(int j = 0; j < 3; j++) {
		        System.out.print(arr[i][j]+" ");
		    }
		    System.out.println();
		}
	}
}

Output:

1 2 3
4 5 6
7 8 8

Array as a Function Argument.

Java passes "objects by reference" and not by values. The array is passed as a reference and not as a copy of individual elements so any change done using array reference will be reflected in the original array. 

Example of an array as a function argument in Java(Sort an Array). 

class SortArray {
    public void sort(int[] newArr) {
        
        int n = newArr.length;
        
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < n-1; j++) {
                if(newArr[j] > newArr[j+1]) {
                    int temp = newArr[j];
                    newArr[j] = newArr[j+1];
                    newArr[j+1] = temp;
                }
            }
        }
    }
}
public class Main
{
	public static void main(String[] args) {
		
		SortArray obj = new SortArray();
		
		int arr[] = {20, 12, 50, 65, 15, 10};
		obj.sort(arr);
		
		for(int i : arr) {
		    System.out.print(i+" ");
		}
	}
}

Output:

10 12 15 20 50 65

The above example program is to sort all the array elements in ascending order. Similarly, we can perform several different operations on an array, like searching an element in an array using different searching methods or sorting the array elements in ascending or descending order.