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08: Web.xml interview questions and answers

Since servlet 3.0 specification, the web.xml file in a web application is optional. The servlet 3.0 API introduced annotations to register servlets. Learn more at Servlet Interview Questions and Answers. Q1. What is a web.xml file? A1. … Read more ›...

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08: Write code to add, subtract, multiply, and divide given numbers?

A trivial coding example (i.e. a Calculator) tackled using the following programming paradigms in Java not only to perform well in coding interviews, but also to learn these programming paradigms.

Approach 1: Procedural Programming
Approaches 2 – 4: Object Oriented Programming
Approach 5: Functional Programming (Java 8)

Approach 1: Procedural

public interface Calculate {
   abstract int calculate(int operand1, int oerand2, Operator operator);
}

public interface Calculate {

abstract int calculate(int operand1, int oerand2, Operator operator);

}

public enum Operator {
   ADD, SUBTRACT, DIVIDE, MULTIPLY;
}

public enum Operator {

ADD, SUBTRACT, DIVIDE, MULTIPLY;

}

public class CalculateImpl implements Calculate {

    @Override
    public int calculate(int operand1, int operand2, Operator operator) {

        switch (operator) {
        case ADD:
            return operand1 + operand2;
        case SUBTRACT:
            return operand1 - operand2;
        case MULTIPLY:
            return operand1 * operand2;
        case DIVIDE:
            return operand1 / operand2;
        }

        throw new RuntimeException(operator + "is unsupported");
    }

}

public class CalculateImpl implements Calculate {

@Override

public int calculate(int operand1, int operand2, Operator operator) {

switch (operator) {

case ADD:

return operand1 + operand2;

case SUBTRACT:

return operand1 - operand2;

case MULTIPLY:

return operand1 * operand2;

case DIVIDE:

return operand1 / operand2;

}

throw new RuntimeException(operator + "is unsupported");

}

public class CalculatorTest {
    public static void main(String[] args) {
       Calculate calc = new CalculateImpl();
       int result = calc.calculate(5,6,Operator.ADD);
       result = calc.calculate(result,6,Operator.MULTIPLY);
       result = calc.calculate(result,1,Operator.SUBTRACT);
       result = calc.calculate(result,5,Operator.DIVIDE);
       
       System.out.println("result=" + result);
    }
}

public class CalculatorTest {

public static void main(String[] args) {

Calculate calc = new CalculateImpl();

int result = calc.calculate(5,6,Operator.ADD);

result = calc.calculate(result,6,Operator.MULTIPLY);

result = calc.calculate(result,1,Operator.SUBTRACT);

result = calc.calculate(result,5,Operator.DIVIDE);

System.out.println("result=" + result);

}

Output: result=13

Approach 2: OOP

public interface MathCommand<E> {
    abstract E execute(E operand1, E operand2);
}

public interface MathCommand<E> {

abstract E execute(E operand1, E operand2);

}

public class AddCommand implements MathCommand<Integer>{

    @Override
    public Integer execute(Integer operand1, Integer operand2) {
        return operand1 + operand2;
    }    
}

public class AddCommand implements MathCommand<Integer>{

@Override

public Integer execute(Integer operand1, Integer operand2) {

return operand1 + operand2;

}

public class SubtractCommand implements MathCommand<Integer>{

    @Override
    public Integer execute(Integer operand1, Integer operand2) {
        return operand1 - operand2;
    }    
}

public class SubtractCommand implements MathCommand<Integer>{

@Override

public Integer execute(Integer operand1, Integer operand2) {

return operand1 - operand2;

}

public class MultiplyCommand implements MathCommand<Integer>{

    @Override
    public Integer execute(Integer operand1, Integer operand2) {
        return operand1 * operand2;
    }    
}

public class MultiplyCommand implements MathCommand<Integer>{

@Override

public Integer execute(Integer operand1, Integer operand2) {

return operand1 * operand2;

}

public class DivideCommand implements MathCommand<Integer>{

    @Override
    public Integer execute(Integer operand1, Integer operand2) {
        return operand1 / operand2;
    }    
}

public class DivideCommand implements MathCommand<Integer>{

@Override

public Integer execute(Integer operand1, Integer operand2) {

return operand1 / operand2;

}

public class CalculatorTest2 {
    public static void main(String[] args) {
        MathCommand<Integer> command = new AddCommand();
        Integer result = command.execute(5, 6);
        command = new MultiplyCommand();
        result = command.execute(result, 6);
        command = new SubtractCommand();
        result = command.execute(result, 1);
        command = new DivideCommand();
        result = command.execute(result, 5);

        System.out.println("result=" + result);
    }
}

public class CalculatorTest2 {

public static void main(String[] args) {

MathCommand<Integer> command = new AddCommand();

Integer result = command.execute(5, 6);

command = new MultiplyCommand();

result = command.execute(result, 6);

command = new SubtractCommand();

result = command.execute(result, 1);

command = new DivideCommand();

result = command.execute(result, 5);

System.out.println("result=" + result);

}

When you have more mathematical operations,

…

09: 11 SOAP Web service interview Q&As

SOAP Web Services interview Questions & Answers Links: 6 Java RESTful Web services Interview | 5 JAXB interview Questions & Answers | Java Web Services interview Questions & Answers Q1. What are the different approaches to developing a SOAP based Web service? … Read more ›...

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09: Java FP – CompletableFuture Error Handling

handle(…) returns a result or an exception A dummy exception is thrown from “f” to demonstrate an exceptional scenario. The “java.util.concurrent.ExecutionException” potentially thrown by f.get(), g.get(), and h.get() is a checked exception. Hence catching it and re throwing as an unchecked (i.e. RuntimeException) exception.

package com.fp.eg7;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

public class CompletableFutureChainingMain {

    public static void main(String[] args) throws InterruptedException, ExecutionException {

        CompletableFuture<String> f = CompletableFuture.supplyAsync(() -> {  // non-blocking
            delay(6);
            if(1==1) {
                throw new RuntimeException("Dummy error for testing...");
            }
            return "Hello";
        });

        CompletableFuture<String> g = CompletableFuture.supplyAsync(() -> {  // non-blocking
            delay(6);
            return " World";
        });
        
        CompletableFuture<String> h = CompletableFuture.supplyAsync(() -> {  // non-blocking
            delay(6);
            return " !!!!!!";
        });

        //combine the results
        CompletableFuture<String> j = CompletableFuture.supplyAsync(() -> {    
            try {
                return f.get() + g.get() + h.get(); // blocking calls
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
                
        }).handle((r,e) -> r != null ? r :  e.getMessage() );
        
        System.out.println("Reached here..."); // printed immediately
        System.out.println(j.get()); // blocked
    }

    private static final void delay(long delayBy) {
        try {
            TimeUnit.SECONDS.sleep(delayBy);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

package com.fp.eg7;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.TimeUnit;

public class CompletableFutureChainingMain {

public static void main(String[] args) throws InterruptedException, ExecutionException {

CompletableFuture<String> f = CompletableFuture.supplyAsync(() -> { // non-blocking

delay(6);

if(1==1) {

throw new RuntimeException("Dummy error for testing...");

}

return "Hello";

});

CompletableFuture<String> g = CompletableFuture.supplyAsync(() -> { // non-blocking

delay(6);

return " World";

});

CompletableFuture<String> h = CompletableFuture.supplyAsync(() -> { // non-blocking

delay(6);

return " !!!!!!";

});

//combine the results

CompletableFuture<String> j = CompletableFuture.supplyAsync(() -> {

try {

return f.get() + g.get() + h.get(); // blocking calls

} catch (Exception e) {

throw new RuntimeException(e);

}

}).handle((r,e) -> r != null ? r : e.getMessage() );

System.out.println("Reached here..."); // printed immediately

System.out.println(j.get()); // blocked

}

private static final void delay(long delayBy) {

try {

TimeUnit.SECONDS.sleep(delayBy);

} catch (InterruptedException e) {

e.printStackTrace();

}

Output “Reached here…” … Read...

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09: Java FutureTask example

Java 5 introduced the concurrent package for more efficient multi-threading.

Q. What is the difference between Future and FutureTask in asynchronous processing?
A. Future is the interface and FutureTask is the base implementation of the Future with methods to start and cancel a computation.

…

09: When to use which Java data structure? and why?

List, Set, Map, and Queue(access the ends FIFO or LIFO) are the basic Java data structure interfaces for which there are different implementations to cater for different usage patterns. Java data structure interview questions are very popular, … Read more ›...

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10: 8 Java Maps & Caching Data in Java Interview Q&As

Q1. What is the purpose of a Map interface in Java collection API? A1. A map is a set of associations between pairs of objects. One is known as a “key” and the other is known as a “value”. It is used very frequently in programming in case where for...

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10: ExecutorService Vs Fork/Join & Future Vs CompletableFuture Interview Q&As

Q1. What is the difference between “ExecutorService” and “Fork/Join Framework“?
A1. The Fork/Join framework uses a special kind of thread pool known as the ForkJoinPool, which is a specialized implementation of ExecutorService implementing the 1) work-stealing algorithm,

…

10: SOAP Web Service Styles Interview Q&A

Q1. What is the difference between the “RPC” and “Document” styles in SOAP? A1. There are two communication style models that are used to translate a WSDL binding to a SOAP message body. In RPC style, the body of the SOAP request body must contain both the 1) “operation name...

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10: Spring, JavaConfig (i.e @Configuration), JPA & Hibernate by example

Example #1 Wiring JDBC Datasource


@Configuration
@ImportResource("application.yml")
public class AppConfig
{
    @Autowired
    private Environment environment;

    @Bean
    public DriverManagerDataSource datasource() {
        DriverManagerDataSource ds = new DriverManagerDataSource();
        ds.setDriverClassName(environment.getRequiredProperty("spring.datasource.driver-class-name"));
        ds.setUrl(environment.getRequiredProperty("spring.datasource.url"));
        ds.setUsername(environment.getRequiredProperty("spring.datasource.username"));
        ds.setPassword(environment.getRequiredProperty("spring.datasource.password"));
        return ds;
    }
}

@Configuration

@ImportResource("application.yml")

public class AppConfig

{

@Autowired

private Environment environment;

@Bean

public DriverManagerDataSource datasource() {

DriverManagerDataSource ds = new DriverManagerDataSource();

ds.setDriverClassName(environment.getRequiredProperty("spring.datasource.driver-class-name"));

ds.setUrl(environment.getRequiredProperty("spring.datasource.url"));

ds.setUsername(environment.getRequiredProperty("spring.datasource.username"));

ds.setPassword(environment.getRequiredProperty("spring.datasource.password"));

return ds;

}

application.yml where the datasource properties are read from.


############
# Datasource properties
############
spring:

  datasource:
    driver-class-name: com.sybase.jdbc4.jdbc.SybDataSource
    url: jdbc:sybase:Tds:mydbhost:5700/my_db
    username: user
    password: pwd

############

# Datasource properties

############

spring:

datasource:

driver-class-name: com.sybase.jdbc4.jdbc.SybDataSource

url: jdbc:sybase:Tds:mydbhost:5700/my_db

username: user

password: pwd

Example #2 Wiring JDBC Datasource with JNDI


@Configuration
@ImportResource("application.yml")
public class AppConfig
{
    @Autowired
    private Environment environment;

    @Bean
    public DataSource dataSource() {
        final JndiDataSourceLookup jndiLookup = new JndiDataSourceLookup();
        final String dataSourceJndi = environment.getRequiredProperty("spring.datasource.jndi");
        return jndiLookup.getDataSource(dataSourceJndi);
    }
}

@Configuration

@ImportResource("application.yml")

public class AppConfig

{

@Autowired

private Environment environment;

@Bean

public DataSource dataSource() {

final JndiDataSourceLookup jndiLookup = new JndiDataSourceLookup();

final String dataSourceJndi = environment.getRequiredProperty("spring.datasource.jndi");

return jndiLookup.getDataSource(dataSourceJndi);

}

Example #3 Wiring the JPA persistence unit processors Callback interface for post-processing a JPA PersistenceUnitInfo. … Read more ›...

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10+ Domain Driven Design (i.e. DDD) Interview Q&As

Q1. What is Domain Driven Design (i.e. DDD)? What is DDD oriented microservice? A1. Domain-driven design advocates modelling based on the reality of business as relevant to your use cases. In the context of building applications, DDD talks about problems as domains. If you are building a shopping cart application,...

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10+ Key Java Microservices Interview Questions & Answers

Java microservices interview questions and answers covering microservices patterns, best practices, Springboot and Spring cloud . Q1. How will you go about choosing REST vs Messaging for Microservices? A1. Microservices can be invoked both synchronously and asynchronously. Microservices must be organized around business functionalities like Customers, … Read more ›...

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11: JAX-WS how to create a SOAP web service in Java?

Step 1:Create the Java Maven project:

mvn archetype:generate -DgroupId=com.mytutorial -DartifactId=simpleSoapWeb -DarchetypeArtifactId=maven-archetype-webapp

1	mvn archetype:generate -DgroupId=com.mytutorial -DartifactId=simpleSoapWeb -DarchetypeArtifactId=maven-archetype-webapp

Step 2: Need the libraries/frameworks

This example shows Apache CXF library as JAX-WS implementation with Spring and deployed to JBoss server 5.1.1.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.mytutorial</groupId>
    <artifactId>simpleSoapWeb</artifactId>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>simpleSoapWeb Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <properties>
        <cxf.version>2.7.9</cxf.version>
        <javax-servlet.version>3.0.1</javax-servlet.version>
        <spring.version>3.1.0.RELEASE</spring.version>
    </properties>

    <dependencies>
        <!-- JAX-WS -->
        <!-- apache cxf -->
        <dependency>
            <groupId>org.apache.cxf</groupId>
            <artifactId>cxf-rt-frontend-jaxws</artifactId>
            <version>${cxf.version}</version>
        </dependency>

        <dependency>
            <groupId>org.apache.cxf</groupId>
            <artifactId>cxf-rt-transports-http</artifactId>
            <version>${cxf.version}</version>
        </dependency>

        <!-- Servelet API -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <scope>provided</scope>
            <version>${javax-servlet.version}</version>
        </dependency>

        <!-- Spring -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <scope>compile</scope>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.0</version>
        </dependency>
    </dependencies>
    <build>
        <finalName>simpleSoapWeb</finalName>
    </build>
</project>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

<groupId>com.mytutorial</groupId>

<artifactId>simpleSoapWeb</artifactId>

<version>1.0-SNAPSHOT</version>

<name>simpleSoapWeb Maven Webapp</name>

<url>http://maven.apache.org</url>

<cxf.version>2.7.9</cxf.version>

<javax-servlet.version>3.0.1</javax-servlet.version>

<spring.version>3.1.0.RELEASE</spring.version>

</properties>

<groupId>org.apache.cxf</groupId>

<artifactId>cxf-rt-frontend-jaxws</artifactId>

<version>${cxf.version}</version>

</dependency>

<groupId>org.apache.cxf</groupId>

<artifactId>cxf-rt-transports-http</artifactId>

<version>${cxf.version}</version>

</dependency>

<groupId>javax.servlet</groupId>

<artifactId>javax.servlet-api</artifactId>

<scope>provided</scope>

<version>${javax-servlet.version}</version>

</dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-web</artifactId>

<scope>compile</scope>

<version>${spring.version}</version>

</dependency>

</dependency>

</dependencies>

<build>

<finalName>simpleSoapWeb</finalName>

</build>

</project>

Step 3: Web service interface with JAX-WS annotations

Folder: src/main/java

package com.mytutorial;

import javax.jws.WebMethod;
import javax.jws.WebService;

@WebService
public interface SimpleSoapWeb {

    @WebMethod
    public String sayHello(String name);
}

package com.mytutorial;

import javax.jws.WebMethod;

import javax.jws.WebService;

@WebService

public interface SimpleSoapWeb {

@WebMethod

public String sayHello(String name);

}

Step 4: Implementation of Web service interface

package com.mytutorial;

import javax.jws.WebService;

@WebService(endpointInterface = "com.mytutorial.SimpleSoapWeb", serviceName="simpleSoapService")
public class SimpleSoapWebImpl implements SimpleSoapWeb {

    public String sayHello(String name) {
        String result = "Hello " + name;
        return result;
    }
}

package com.mytutorial;

import javax.jws.WebService;

@WebService(endpointInterface = "com.mytutorial.SimpleSoapWeb", serviceName="simpleSoapService")

public class SimpleSoapWebImpl implements SimpleSoapWeb {

public String sayHello(String name) {

String result = "Hello " + name;

return result;

}

Step 5: Spring XML config as IoC.

…

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Categories

Blog Archives

08: Web.xml interview questions and answers

08: Write code to add, subtract, multiply, and divide given numbers?

09: 11 SOAP Web service interview Q&As

09: Java FP – CompletableFuture Error Handling

09: Java FutureTask example

09: When to use which Java data structure? and why?

10: 8 Java Maps & Caching Data in Java Interview Q&As

10: ExecutorService Vs Fork/Join & Future Vs CompletableFuture Interview Q&As

10: SOAP Web Service Styles Interview Q&A

10: Spring, JavaConfig (i.e @Configuration), JPA & Hibernate by example

10+ Domain Driven Design (i.e. DDD) Interview Q&As

10+ Key Java Microservices Interview Questions & Answers

11: JAX-WS how to create a SOAP web service in Java?

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