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Java Array Interview Questions for Entry-Level Developers Part 01

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1. What is a Java array? (Definition, purpose, characteristics: fixed size, contiguous memory) Definition A Java array is a data structure that allows storing multiple values of the same data type in a contiguous block of memory. It is a fixed-size collection of elements, each identified by an index. Purpose Arrays are used to efficiently store and manage a collection of data. They provide: Fast access to elements using an index. Memory efficiency since elements are stored contiguously. Characteristics Fixed Size When an array is declared, its size must be specified. The size cannot be changed dynamically (for dynamic collections, use ArrayList or other collections). Contiguous Memory Allocation Arrays are stored in a continuous block of memory, making access faster compared to linked lists. Indexed Access Elements are accessed using zero-based indexing, e.g., array[0] refers to the first element. Homogeneous Elements All elements in an array must be of the same data type. Efficien...
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Message pubish in goolge cloud pubsub topic with java client

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Table Of Contents What is Pub/Sub? What are the benefits of using Pub/Sub? Core concepts of Pub/sub. How to publish a message in pub/sub topic in java with credentials? Shutdown publisher when application stop or no need publisher.  GitHub project link of reusable module.  How to publish and receive a message in pub/sub in cloud console? Conclusion.  What is Pub/Sub? Cloud Pub/Sub is a fully-managed messaging service provided by Google Cloud Platform. It is designed to provide reliable, scalable, and real-time messaging between applications and services. Cloud Pub/Sub allows you to publish and consume messages from any application or service, regardless of the language or platform they are built on. It provides a simple and flexible architecture that decouples your systems and allows them to work independently. In Cloud Pub/Sub, you can create one or more topics to which you can publish messages. Subscribers can then subscribe to the topic and receive all published messag...
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JPA vs Spring JPA vs Spring Data JPA vs Hibernate

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JPA is the Java Persistence API , which is Java 's standard API for object-relational mapping . JPA is only an specification - you need an implementation of it to be able to use it. Hibernate is one of the most well-known and most used implementations of JPA, but there are others, such as EclipseLink JPA . The Spring Framework is a large framework to help you write enterprise-grade software easier. It contains support for many Java technologies, including JPA. The Spring Framework consists of a collection of projects , and one of these projects is Spring Data . The goal of Spring Data is to make it easier to work with different kinds of databases, from traditional relational databases to NoSQL databases. Spring Data supports JPA via the Spring Data JPA subproject. To write a program that uses JPA, you need at least a JPA implementation, such as Hibernate. If you are using the Spring Framework for your application, you will most likely want to use Spring Data JP...
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Building Jersey Restful Web Services in Spring Boot.

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What you need? Following are needed: java 8 maven 3.2 spring boot 1.5.8.RELEASE Maven pom.xml We will add  spring-boot-starter-parent  as a parent of our maven-based project. The added benefit of this is version management for Spring dependencies. < parent > < groupId > org.springframework.boot </ groupId > < artifactId > spring-boot-starter-parent </ artifactId > < version > 1.5.0.RELEASE </ version > </ parent > Adding the Spring-Boot-Starter-Jersey Dependency This will add/configure the Jersey-related dependencies. < dependency > < groupId > org.springframework.boot </ groupId > < artifactId > spring-boot-starter-jersey </ artifactId > </ dependency > The Full pom.xml <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apach...
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About Spring @Component, @Repository, @Service and @Controller Annotations.

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Spring @Component , @Service , @Repository and @Controller annotations are used for automatic bean detection using classpath scan in Spring framework. These four  annotations are same logically. Differences between @Component, @Repository, @Controller and @Service: @Component  This is a general-purpose stereotype annotation(auto scan) indicating that the class is a spring component. @Component annotation picks them up and registers their following classes as beans, just as if they were annotated with @Component . @Repository This is special type of @Component annotation.   This is to indicate that the class defines a data repository.  @Controller This is special type of @Component annotation. The @Controller annotation indicates that a particular class serves the role of a controller. The @Controller annotation acts as a stereotype for the annotated class, indicating its role.  What’s special about @Controller? We cannot...
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Change Liferay Default User Portrait

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Step 1: Add the below given properties in portal-ext.properties file. portal-ext.properties file location : %LIFERAY_HOME%\tomcat-7.0.62\webapps\ROOT\WEB-INF\classes If there no file exists with this name, please create this. And then add below lines. image.default.user.female.portrait=com/images/user_female_portrait.png image.default.user.male.portrait=com/images/user_male_portrait.png Step 2: Add the default custom image under below given path %LIFERAY_HOME%\tomcat-7.0.62\webapps\ROOT\WEB-INF\classes\com\images\ Step 3: Restart the server Enjoy !!!!
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Deploy Spring Boot application on Tomcat

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Deploy Spring Boot application on Tomcat Step #1 Add the following dependency to pom.xml in order to tell Spring Boot not to use its embedded Tomcat. < dependency >      < groupId > org . springframework . boot < / groupId >      < artifactId > spring - boot - starter - tomcat < / artifactId >      < scope > provided < / scope > < / dependency > Step #2 Change the packaging property to war in pom.xml. < properties >        < packaging > war < / packaging > < / properties > Step #3 Replace your initializer class with the following: package com.oms; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.builder.SpringApplicationBuilder; import org.springframework.boot.web.support.SpringBootServ...
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