Tag: java

Categories
data structures java two pointer

two pointer algorithm

two pointer algorithm

Two pointer algorithm is one of the basic and easy data structures for beginners. It is also commonly asked in most of the interview

In this tutorial, we will learn to apply the two pointer algorithm to find the sum of two numbers in a sorted array

Input

given sorted array
let a = {8 , 12, 24, 30, 44, 54, 60, 61}
sum of two numbers 
let x = 98
Output
44,54

Algorithm explanation

  • The Array should be Sorted in ascending
  • initialize a variable as i with starting position as zero
  • initialize a variable as j with starting position as n-1
  • check the sum of index i & j, if matches then print the value
  • else if the sum is less than the target value then increase the i position
  • else decrease the j position

Example

public class TwoPointersExample {

    private void sumofTwoNumbers(int a[], int x) {
        if (a != null && a.length > 0) {
            int i = 0;
            int j = a.length - 1;
            boolean isFound = false;
            while (i < j) {
                int sum = a[i] + a[j];
                if (x == sum) {
                    System.out.println("The value is " + a[i] + " " + a[j]);
                    isFound = true;
                    break;
                } else if (sum < x) {
                    i++;
                } else {
                    j--;
                }
            }
            if (!isFound) {
                System.out.println("Not able to find with given input");
            }

        } else {
            System.out.println("Not a valid input");
        }

    }

    public static void main(String[] args) {
        int a[] = {8, 12, 24, 30, 44, 54, 60, 61};
        TwoPointersExample example = new TwoPointersExample();
        example.sumofTwoNumbers(a, 98);
        ;
    }
}

Output

The value is 44 54

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binary search algorithm
Categories
data structures insertion sort java

insertion sort algorithm

In this article, we will discuss the simple sorting algorithm called insertion sort.

What is insertion sort?

This works in a similar fashion as playing a deck of cards. Assuming two different parts – sorted and unsorted, we need to pick and sort each card from an unsorted part into a sorted part.

Steps to be folowed

The first element in an array is to be considered as already sorted.

The next element is to be taken and compared with the elements in a sorted array.

Insert the element by shifting the elements in the sorted array which are greater than the value to be sorted

Example

import java.util.Arrays;

public class InsertionSort {

	private void sortArray(int[] arr) {

		for (int i = 1; i < arr.length; i++) {
			int key = arr[i];
			int j = i - 1;
			while (j >= 0 && arr[j] > key) {
				arr[j + 1] = arr[j];
				j--;
			}
			arr[j + 1] = key;
		}

	}

	public static void main(String[] args) {
		InsertionSort insertionSort = new InsertionSort();
		int[] arr = { 2, 7, 5, 8, 3, 4, 1, 6 };
		insertionSort.sortArray(arr);
		System.out.println(Arrays.toString(arr));
	}

}

Output

[1, 2, 3, 4, 5, 6, 7, 8]

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selection sort
Categories
data structures java selection sort

selection sort

selection sort

In this post, We will learn about the selection sort algorithm in the java language. It is a comparison-based sorting algorithm

Selection sort will select the element from an array, and keep on compare with the remaining elements.

End of each iteration we will obtain the minimum value, After that we will swap the minimum element to the sorted array

Likewise, it will select all the elements in the array and compare them with the remaining element 

Unsorted Input array: [ 12, 4, 6, 7, 2, 5 ]
Sorted Output array:  [ 2, 4, 5, 6, 7, 12 ]

Execution Steps

  1. [2, 4, 6, 7, 12, 5]
  2. [2, 4, 6, 7, 12, 5]
  3. [2, 4, 5, 7, 12, 6]
  4. [2, 4, 5, 6, 12, 7]
  5. [2, 4, 5, 6, 7, 12]

Selection Sort

Time Complexity : O(n^2)

Code

package example;

import java.util.Arrays;

public class SelectionSort {

	private void sortArray(int[] arr) {

		for (int i = 0; i < arr.length; i++) {
			int selectionItem = i;
			for (int j = i + 1; j < arr.length; j++) {
				if (arr[j] < arr[selectionItem]) {
					selectionItem = j;
				}
			}
			int temp = arr[selectionItem];
			arr[selectionItem] = arr[i];
			arr[i] = temp;
		}
	}

	public static void main(String[] args) {
		int[] arr = { 12, 4, 6, 7, 2, 5 };
		SelectionSort selectionSort = new SelectionSort();
		selectionSort.sortArray(arr);
		System.out.println(Arrays.toString(arr));
	}
}

Output

[2, 4, 5, 6, 7, 12]

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bubble sort algorithm
Categories
Bubble sort data structures java

bubble sort algorithm

bubble sort algorithm

In this post, we will learn about the bubble sort algorithm. The bubble sort algorithm is one of the important sorting algorithms

It will compare two adjacent elements in an array and swap the right value to the left if it is lesser than left

Bubble Sort

Time Complexity: O(n^2)
Values1012462
Position01234
Input Array
Step 1
Iterate the given array using for loop
Step 2 
Add one more iteration within the for loop again
Step 3
compare the first element with second element
Step 4 
If first element greater than second element swap the two elements
Step 5 
Compare the second element with third element 
Step 6
If Second element is greater than third element, then swap the two elements 
Step 7 
Continue until nth element
Step 1
Step2
Step 3
Step 4
Result of the first iteration

Java Implementation 


public class BubbleSort {

	private void sortArray(int arr[]) {
		for (int i = 0; i < arr.length; i++) {
			boolean isSwap = false;
			for (int j = 0; j < arr.length - i - 1; j++) {
				if (arr[j] > arr[j + 1]) {
					int temp = arr[j + 1];
					arr[j + 1] = arr[j];
					arr[j] = temp;
					isSwap = true;
				}
			}
			if (!isSwap) {
				break;
			}
		}
	}

	public static void main(String[] args) {
		int arr[] = { 10, 12, 4, 6, 2 };
		System.out.println("Array Before sorting");
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + "  ");
		}
		BubbleSort bubbleSort = new BubbleSort();
		bubbleSort.sortArray(arr);

		System.out.println("\nArray After Sorting");
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + "  ");
		}

	}

}

Output

Array Before sorting
10  12  4  6  2  
Array After Sorting
2  4  6  10  12
search in rotated sorted array
Categories
binary search data structures java

binary search algorithm

Binary search algorithm is one of the fastest way to identify the element from an sorted array. It is also the commonly asked data structure interview questions.

It works based on divide and conquer mechanism. It will divide the given array into 2 parts and discard the one part. So it will works faster for a big array compared to linear search.

Time complexity of Binary Search is O(logn)

Below is the give array structure

With the above given array we have to find the position of 9, Using linear search we can find easily, But the time complexity will be O(N)

Below is java code snippet to find the position using Binary Search 

public class BinarySearchExample {

	private int binarySearch(int[] array, int target) {
		int leftIndex = 0;
		int rightIndex = array.length - 1;
		while (leftIndex <= rightIndex) {
			// find the middle Index
			int middleIndex = (leftIndex + rightIndex) / 2;
			if (array[middleIndex] == target) {
				return middleIndex;
			}
			if (target > array[middleIndex]) {
				// ignoring the left side of array
				leftIndex = middleIndex + 1;
			} else {
				// ignoring the right side of array
				rightIndex = middleIndex - 1;
			}
		}
		return -1;
	}

	public static void main(String[] args) {
		int[] i = { 2, 3, 5, 6, 7, 9,10 };
		int targetNumber = 9;
		BinarySearchExample object = new BinarySearchExample();
		int output = object.binarySearch(i, targetNumber);
		System.out.println(output);
	}

}
Output
5

Categories
java

automatic mouse mover in java

while loop in java

In this post, we will do automatic mouse mover in java

We can move the cursor with random directions using below code

Example
import java.awt.Robot;

public class MouseMover {

	public static void main(String[] args) {
		try {
			int xCord = 10;
			int yCord = 20;
			while (true) {

				Robot robot = new Robot();
				robot.mouseMove(xCord++, yCord++);
				System.out.println("Moving mouse to " + xCord + " " + yCord);
				Thread.sleep(10000);
			}

		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}
Github

https://github.com/rkumar9090/student-example/blob/master/src/main/java/com/beginnersbug/example/mouse/MouseMover.java

Categories
java spring-boot

enable cors in spring boot rest API

database password encryption in spring boot

In this post we will learn to enable cors in spring boot rest API

For security reasons, browsers prohibit AJAX calls to resources residing outside the current origin.

While we facing cors issue, we need to enable cors in spring boot application explicitly

Enable for whole spring boot

We need to add below class in our spring boot application, this will enable cors for all endpoints 

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
public class CorsConfig {

	public WebMvcConfigurer corsConfigure() {
		return new WebMvcConfigurerAdapter() {
			public void addCorsMappings(CorsRegistry registry) {
				registry.addMapping("/**");
			}
		};
	}

}
Enable for specific endpoint

Below snippet will enable cors only for endpoint which starts with /api


import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
public class CorsConfig {

	public WebMvcConfigurer corsConfigure() {
		return new WebMvcConfigurerAdapter() {
			public void addCorsMappings(CorsRegistry registry) {
				registry.addMapping("/api/**");
			}
		};
	}

}
Enable for specific orgins

Below snippet will enable for orgin https://beginnersbug.com

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
public class CorsConfig {

	public WebMvcConfigurer corsConfigure() {
		return new WebMvcConfigurerAdapter() {
			public void addCorsMappings(CorsRegistry registry) {
				registry.addMapping("/api/**")
				.allowedOrigins("https://beginnersbug.com");
			}
		};
	}

}
Enable CORS with Annotation

we can enable cors by annotation. we need to mention @crossOrgin annotation in the controller class as like below 


import java.util.List;
import java.util.Optional;

import javax.validation.Valid;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.beginnersbug.studentservice.dao.StudentDao;
import com.beginnersbug.studentservice.model.Student;

@RestController()
@CrossOrigin()
@RequestMapping("/api/student")
public class StudentController {

	@Autowired
	StudentDao studentsDao;

	@RequestMapping(method = RequestMethod.GET)
	public List<Student> getStudentsList() {
		return studentsDao.findAll();
	}
}
Github

https://github.com/rkumar9090/student-service/blob/master/src/main/java/com/beginnersbug/studentservice/CorsConfig.java

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Categories
collections java

join two arraylist in java with example

while loop in java

In this post, we will learn to join two arraylist in java with example

ArrayList is a dynamic array concept in java. We use ArrayList in so many places.

Syntax
list1.addAll(list2);

From the above syntax list2 will added to list1.

Example
import java.util.ArrayList;
import java.util.List;

public class Join2List {

	public static void main(String[] args) {
		try {
			List<String> list1 = new ArrayList<String>();
			List<String> list2 = new ArrayList<String>();

			list1.add("Rajesh");
			list1.add("Usha");

			list2.add("Kumar");
			list2.add("Nandhini");

			System.out.println("---List1 value before adding list2---");
			for (String string : list1) {
				System.out.println(string);
			}

			// Adding list2 to list1
			list1.addAll(list2);

			System.out.println("---List1 value After adding list2---");

			for (String string : list1) {
				System.out.println(string);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}
Output
---List1 value before adding list2---
Rajesh
Usha
---List1 value After adding list2---
Rajesh
Usha
Kumar
Nandhini
Github

https://github.com/rkumar9090/BeginnersBug/blob/master/BegineersBug/src/com/geeks/example/list/Join2List.java

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Categories
java

singleton in java with example

while loop in java

In this post, we will learn singleton in java with example

Singleton is one of the famous design pattern in java. Below are few point of Singleton

  • We Should have the only one instance in the application
  • In below example, we are going to use Lazy Initialization
  • It will create an instance when the application in need
  • We should have a private constructor to avoid outside initialization
public class SingletonExample {

	public static SingletonExample singletonExampleObject = null;

	public String stringVarible = "Singleton string";

	private SingletonExample() {

	}

	public static SingletonExample getSingletonInstance() {
		if (null == singletonExampleObject) {
			singletonExampleObject = new SingletonExample();
		}
		return singletonExampleObject;
	}

}

The above class is an example of Singleton. As mentioned in the above sentence we have a private constructor and static instance of the class

public class Example {

	public static void main(String[] args) {
		try {
			SingletonExample singletonObject = SingletonExample.getSingletonInstance();
			System.out.println(singletonObject.stringVarible);
			singletonObject.stringVarible = "BeginnersBug";

			// Creating another object
			SingletonExample singletonInstance = SingletonExample.getSingletonInstance();
			System.out.println(singletonInstance.stringVarible);
		} catch (Exception e) {
			e.printStackTrace();

		}
	}

}
Singleton string
BeginnersBug

Even though we have two variables for SingletonExample it is sharing same instance

So the Value of stringVaraible is reflected on the second variable

Conclusion

In the above post, we learned about singleton in java with example

Github

https://github.com/rkumar9090/student-example/tree/master/src/main/java/com/beginnersbug/example/singleton

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convert java object to JSON string

Categories
java

convert java object to JSON string

while loop in java

In this post, we will learn to convert java object to JSON string using GSON library

We can convert Java object to json string using below dependency

Dependency
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.5</version>
</dependency>
Syntax
String jsonString = gson.toJson(student);
Example

import com.beginnersbug.example.model.Student;
import com.google.gson.Gson;

public class ConvertJavaToJson {

	public static void main(String[] args) {
		Gson gson = new Gson();
		Student student = new Student();
		student.setStudentId("001");
		student.setStudentName("Rajesh");
		student.setDepartment("JAVA");
		student.setSchoolName("BeginnersBug");

		String jsonString = gson.toJson(student);

		System.out.println(jsonString);

	}
}
Student.java
public class Student {

	private String studentId;

	private String studentName;

	private String schoolName;

	private String department;

	public String getStudentId() {
		return studentId;
	}

	public void setStudentId(String studentId) {
		this.studentId = studentId;
	}

	public String getStudentName() {
		return studentName;
	}

	public void setStudentName(String studentName) {
		this.studentName = studentName;
	}

	public String getSchoolName() {
		return schoolName;
	}

	public void setSchoolName(String schoolName) {
		this.schoolName = schoolName;
	}

	public String getDepartment() {
		return department;
	}

	public void setDepartment(String department) {
		this.department = department;
	}

}
Output
{"studentId":"001","studentName":"Rajesh","schoolName":"BeginnersBug","department":"JAVA"}
Github

https://github.com/rkumar9090/student-example/blob/master/src/main/java/com/beginnersbug/example/ConvertJavaToJson.java

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