Why do I get ArrayIndexOutOfBoundsException in Java?

By I Wayan Saryada in Basic, Lang Package 1 Comment

The ArrayIndexOutOfBoundsException exception is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.

Array with 10 elements

For example see the code snippet below:

String[] vowels = new String[]{"a", "i", "u", "e", "o"}
String vowel = vowels[10]; // throws the ArrayIndexOutOfBoundsException

Above we create a vowels array with five elements. This will make the array have indexes between 0..4. On the next line we tried to access the tenth element of the array which is illegal. This statement will cause the ArrayIndexOutOfBoundsException thrown.

We must understand that arrays in Java are zero indexed. The first element of the array will be at index 0 and the last element will be at index array-size - 1. So be careful with your array indexes when accessing array elements. For example if you have an array with 5 elements this mean that the index of the array is from 0 to 4.

If you are trying to iterate an array using for loop. Make sure the index start from 0 and execute the loop while the index is less than the length of the array, you can get the length of the array using the array length property. Let’s see the code snippet below:

for (int i = 0; i < vowels.length; i++) {
    String vowel = vowels[i];
    System.out.println("vowel = " + vowel);
}

Or if you don’t need the index you can simplify your code using the for-each or enhanced for-loop statement instead of the classic for loop statement as shown below:

for (String vowel : vowels) {
    System.out.println("vowel = " + vowel);
}

How to create a read-only MySQL user?

By I Wayan Saryada in MySQL 3 Comments

Introduction

There are times when you need to create a user only to have read-only access to a database. The user can view or read the data in the database, but they cannot make any changes to the data or the database structure.

Creating a New User Account

To create a read-only database user account for MySQL do the following steps:

  • First, login as a MySQL administrator from your terminal / command prompt using the following command:
mysql -u root -p
  • You’ll be prompted to enter the password. Type the password for the root account.
  • Create a new MySQL user account.
CREATE USER 'report'@'%' IDENTIFIED BY 'secret';

The % in the command above means that user report can be used to connect from any host. You can limit the access by defining the host from where the user can connect. Omitting this information will only allow the user to connect from the same machine.

  • Grant the SELECT privilege to user.
GRANT SELECT ON kodejava.* TO 'report'@'%';
  • Execute the following command to make the privilege changes saved and take effect.
FLUSH PRIVILEGES;
  • Type quit to exit from the MySQL shell.

Test the New User Account

  • Now we can try the newly created user account. Start by login with the new user account and provide the corresponding password.
mysql -u report -p
  • Try executing the DELETE command:
mysql> USE kodejava;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> DELETE FROM authors;
ERROR 1142 (42000): DELETE command denied to user 'report'@'localhost' for table 'authors'
mysql> UPDATE authors SET name = 'Wayan Saryada' WHERE id = 1;
ERROR 1142 (42000): UPDATE command denied to user 'report'@'localhost' for table 'authors'
mysql>

Step-By-Step Guide to Creating and Inserting a Java API in Eclipse

By Danish Wadhwa in Eclipse, Tools 2 Comments

Eclipse is the most popular Java Integrated Development Environment (IDE). Just check out the survey result.

**Image Source: **IProgrammer

Here is one more for you.

Image Source Qiita

Some people say that Eclipse is dying. However, we can see that many developers still prefer using Eclipse. Let’s get Eclipse popularity part out of the way and talk about how you can insert a Java API in Eclipse. You can do it quickly. But before getting to adding and creating API, I will educate about Java API for readers who do not have in-depth knowledge of Java API.

What is Java API?

The full form of API is Application Programming Interface (API). Java language comprises various syntax and semantics. The set of classes that are inside the Java Development Environment is known as Java API.

The classes in Java API is in Java language, and it runs via a Java Virtual Machine. You can find every single thing inside Java API, ranging from collection classes to GUI classes.

To get the most out of Java API, you need to have a firm grasp of Java programming language. Java is the most popular language in the world today, and huge corporations love Java due to its great documentation and security features.

If you want to land a project in Java, it is beneficial to undertake a Java Certification Training course that gives clear insights about various aspect of the language being a big plus for novice as well as tech professionals.

There are various levels in Java certification courses. You can slowly jump from one level to the another and learn as you go. You can write some codes on the side while going through the Java certification courses.

How to Create and Insert a Java API in Eclipse?

Now that you are aware of Java API, we can talk about the process of creating and inserting a Java API in Eclipse.

To create a great program without wasting much time, you need to work in a framework. If you are among the developers who are looking to develop your API via Eclipse, you are in the right place. I will show you a step-by-step guide to creating and inserting a Java API in Eclipse. All you need to do is systematically follow my instruction.

Project Creation

The first task is a project creation. Here are the steps:

  • Enter the current workspace inside Eclipse. It is better to create a new workspace to ensure that you do not mess your projects.
  • After the first step, you need to make a new Java Project and give whatever name you like. However, you should make sure that your name relates to your project.
  • After the project creation, you need to test if you can see your project in an explorer window or not. It is essential to make sure that it does not mess around with other projects.

Fresh Package and Class

  • Head to project explorer and right click your project. After selecting a new package, name it. It will act as the main class file.
  • Head to package, click new, and then select class under the source folder. Give a relevant name to the class. Make the class, public and do not make the main method stub in class.
  • After the completion of the first two steps, double-click your class file.

Time to Add Code and Export

  • You can now add some codes to your project. For now, create some random static methods that return something.
  • When you finish adding methods to your class, export it as a jar file. It is a simple process. Go to the project source folder and select Export. Then click on Java and select JAR file. Note down the export location, so that you will be able to access it later. You can then click on the Finish button and let the Eclipse do the rest for you.

Do the Testing

  • You are now all set to do some testing. Just create a project like in step number 1. Name it different this time around.
  • There is no need to export it because it is a test project. Instead of exporting, go with creating a package. Just create a new class and name it “test.” You can now inherit the public static void main method. Select the finish button after completing the process.
  • You will observe a class file with the primary method when you smash the finish button. In case you fail to see the class file, copy the code below.

Create a JAR for Building a Path

You are in the ending part of creating and inserting a Java API. You have a primary method ready. Now, you should add API to a build path of the new project.

  • Select your new project and then go to properties.
  • Select “Java Build Path” on the properties–>window.
  • Select Libraries after entering the “Java Build Path” in the properties menu.
  • Click on “Add External JARs..” and go to your API location and then select open.
  • Click the open button to finish the step number 5.

Time to Run your API

You are finally ready for a climax. You have now created your API. What to do next? Just implement your API and observe your computer screen. If there are errors, go through the article once again to see if you missed something along the way.

Over To You

Did you find it challenging to create and insert Java API to Eclipse? Hopefully not. It is so easy that you can finish the task of creating and adding Java API to Eclipse within 10-30 minutes. After the installation of Java API, you can complete your projects in a shorter period.

Remember, smart programmers not only work hard, but they work smart as well. Creating and inserting Java API to Eclipse is the first step to working smart. I hope you have found value in this article. If you have any confusions, feel free to comment below. I will be more than happy to assist you in your path to getting things done.

How do I define access modifiers in Lombok’s @Getter and @Setter annotations?

By I Wayan Saryada in Project Lombok 0 Comment

By default, when we use the Lombok’s @Getter and @Setter annotations the getters and setters will be created with public access modifier. We can however change the access modifier by setting the AccessLevel of the @Getter and @Setter annotations. The available choices for the access level are AccessLevel.PUBLIC, AccessLevel.PROTECTED, AccessLevel.PACKAGE, AccessLevel.PRIVATE. These enum values correspond to Java’s access modifier. While the AccessLevel.NONE will disable the getter and setter method generation.

package org.kodejava.lombok.support;

import lombok.AccessLevel;
import lombok.Getter;
import lombok.Setter;

@Getter
@Setter
public class Person {
    @Setter(AccessLevel.PROTECTED)
    private String firstName;

    private String lastName;
    private String gender;

    @Getter(AccessLevel.PRIVATE)
    private int age;
}

How we use the Person class show in the snippet below:

package org.kodejava.lombok;

import org.kodejava.lombok.support.Person;

public class PersonDemo {
    public static void main(String[] args) {
        Person person = new Person();
        person.setLastName("Bar");
        person.setGender("M");
        person.setAge(20);

        System.out.println(person.getFirstName());
        System.out.println(person.getLastName());
        System.out.println(person.getGender());
    }
}

If we try to see the generated class of the Person class we can run the following command to disassemble the class.

javap -p -cp . org.kodejava.lombok.support.Person

And we got the following output of the javap command. As we can see that the setFirstName() method have a protected access modifier and the getAge() method have a private access modifier. The other mutator and accessor method all set to public access modifier.

public class org.kodejava.lombok.support.Person {
    private java.lang.String firstName;
    private java.lang.String lastName;
    private java.lang.String gender;
    private int age;
    public org.kodejava.lombok.support.Person();
    public java.lang.String getFirstName();
    public java.lang.String getLastName();
    public java.lang.String getGender();
    public void setLastName(java.lang.String);
    public void setGender(java.lang.String);
    public void setAge(int);
    protected void setFirstName(java.lang.String);
    private int getAge();
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.28</version>
    </dependency>
</dependencies>

Maven Central

How do I generate getters and setters with Lombok?

By I Wayan Saryada in Project Lombok 2 Comments

The following code snippet show you how to use Project Lombok‘s @Getter and @Setter annotations to generate getters and setters method in your POJO (plain old java objects) classes. Using these annotations remove the need to manually implements the mutator and accessor methods. Although most IDE allows you to generate these methods, using Lombok makes your classes look cleaner, especially when you have a long list of fields.

Here is a simple User class with a handful fields. We will use the @Getter and @Setter annotations on the class level. This will generate the getters and setters method for any non-static fields in the class.

package org.kodejava.lombok.support;

import lombok.Getter;
import lombok.Setter;

import java.time.LocalDate;

@Getter
@Setter
public class User {
    private Long id;
    private String username;
    private String password;
    private LocalDate lastLogin;
    private boolean active;
}

Each fields in the class will have its corresponding getter and setter. For example the username field will have the getUsername() and setUsername() method. If the field type is boolean such as active it will generate the method setActive() and isActive() method.

Because the accessor and mutator already handled by Lombok, we can use the User class as if we manually implement the getters and setters method.

package org.kodejava.lombok;

import org.kodejava.lombok.support.User;

import java.time.LocalDate;

public class UserDemo {
    public static void main(String[] args) {
        User user = new User();
        user.setId(1L);
        user.setUsername("foo");
        user.setPassword("secret");
        user.setLastLogin(LocalDate.now());
        user.setActive(true);

        System.out.println(user.getId());
        System.out.println(user.getUsername());
        System.out.println(user.getPassword());
        System.out.println(user.getLastLogin());
        System.out.println(user.isActive());
    }
}

If for some reasons you want to disable the getter and setter on specific field, or you want the change the access level, you can use the AccessLevel enums value for the @Getter and @Setter annotations. For example in the code snippet below the username will have no getter and setter while the lastLogin getter and setter will have protected access modifier. The AccessLevel enums includes PUBLIC, MODULE, PROTECTED, PACKAGE, PRIVATE and NONE.

package org.kodejava.lombok.support;

import lombok.AccessLevel;
import lombok.Getter;
import lombok.Setter;

import java.time.LocalDate;

@Getter
@Setter
public class User {
    private Long id;
    @Getter(AccessLevel.NONE)
    @Setter(AccessLevel.NONE)
    private String username;
    private String password;
    @Getter(AccessLevel.PROTECTED)
    @Setter(AccessLevel.PROTECTED)
    private LocalDate lastLogin;
    private boolean active;
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.28</version>
    </dependency>
</dependencies>

Maven Central