Tutorial Playlist
191 Lessons1. Introduction to Java
2. What is Java?
3. History of Java
4. Java Tutorial for Beginners
5. How Do Java Programs Work?
6. JDK in Java
7. C++ Vs Java
8. Java vs. Python
9. Java vs. JavaScript
10. From Java Source Code to Executable
11. How to Install Java in Linux
12. How to Install Java in Windows 10
13. Java Hello World Program
14. Structure of Java Program and Java Syntax
15. Operators in Java
16. Java If-else
17. Switch Case In Java
18. Loops in Java
19. Infinite loop in Java
20. For Loop in Java
21. For Each Loop in Java
22. Constructor in Java
23. Constructor Overloading in Java
24. Copy Constructor in Java
25. Default Constructor in Java
26. Parameterized Constructors in Java
27. Constructor Chaining In Java
28. Finalize Method in Java
29. Static Method in Java
30. Equals Method in Java
31. Abstract Method in Java
32. toString() Method in Java
33. Difference between equals method in Java
34. Inheritance in Java
35. Multiple Inheritance in Java
36. Hierarchical Inheritance in Java
37. Java Classes and Objects
38. Scanner Class in java
39. All classes in java are inherited from which class
40. What is Nested Class in Java
41. POJO Class in Java
42. Anonymous Class in Java
43. Final Class in Java
44. Object Class in Java
45. Packages in Java
Now Reading
46. Access Modifiers in Java
47. Static Keyword In Java
48. Final Keyword in Java
49. Checked and Unchecked Exceptions in Java
50. User Defined Exception in Java
51. Error vs. Exception in Java
52. Java Collection
53. Collections in Java
54. Garbage Collection in Java
55. Generics In Java
56. Java Interfaces
57. Functional Interface in Java
58. Marker Interface in Java
59. Streams in Java
60. Byte stream in java
61. File Handling in Java
62. Thread in Java
63. Thread Lifecycle In Java
64. Daemon Thread in Java
65. Thread Priority in Java
66. Deadlock in Java
67. String Pool in Java
68. Java Database Connectivity(JDBC)
69. Design Patterns in Java
70. Functional Programming in Java
71. OOP vs Functional vs Procedural
72. Heap Memory and Stack Memory in Java
73. Applet in Java
74. Java Swing
75. Java Frameworks
76. Hibernate Framework
77. JUnit Testing
78. How to Install Eclipse IDE for Java?
79. Command line arguments in Java
80. Jar file in Java
81. Java Clean Code
82. OOPs Concepts in Java
83. Java OOPs Concepts
84. Overloading vs Overriding in Java
85. Java 8 features
86. String in Java
87. String to int in Java
88. Why String Is Immutable in Java?
89. Primitive Data Types in Java
90. Non-Primitive Data Types in Java
91. This and Super Keyword in Java
92. HashMap in Java
93. Comparable And Comparator in Java
94. Type Casting in Java
95. Arrays Sort in Java with Examples
96. Variable Hiding and Variable Shadowing in Java
97. Enum in Java
98. Substring in Java
99. Pattern Programs in Java
100. Hashcode in Java
101. What is ByteCode in Java?
102. How To Take Input From User in Java
103. GCD of Two Numbers in Java
104. Linked List in Java
105. Arithmetic Operators in Java
106. Conditional Operators in Java
107. Stack and Queue in Java
108. Array Length in Java
109. Number Pattern Program in Java
110. Split in java
111. Map In Java
112. Difference Between Throw and Throws in Java
113. Difference Between Data Hiding and Abstraction
114. HashSet in Java
115. String Length in Java
116. Factorial Using Recursion in Java
117. DateFormat in Java
118. StringBuilder Class in java
119. Instance variables in Java
120. Java List Size
121. Java APIs
122. Reverse an Array in Java
123. StringBuffer and StringBuilder Difference in Java
124. Java Program to Add Two Numbers
125. String to Array in Java
126. Regular Expressions in Java
127. Identifiers in Java
128. Data Structures in Java
129. Set in Java
130. Pass By Value and Call By Reference in Java
131. Try Catch in Java
132. Bubble Sort in Java
133. Caesar Cipher Program in Java
134. Queue in Java
135. Object Creation in Java
136. Multidimensional Array in Java
137. How to Read a File in Java
138. String Comparison in Java
139. Volatile Keyword in Java
140. Control Statements in Java
141. Jagged Array in Java
142. Two-Dimensional Array in Java
143. Java String Format
144. Replace in Java
145. charAt() in Java
146. CompareTo in Java
147. Matrix Multiplication in Java
148. Static Variable in Java
149. Event Handling in Java
150. parseInt in Java
151. Java ArrayList forEach
152. Abstraction in Java
153. String Input in Java
154. Logical Operators in Java
155. instanceof in Java
156. Math Floor in Java
157. Selection Sort Java
158. int to char in Java
159. Stringtokenizer in java
160. Implementing and Manipulating Abs in Java
161. Char array to string in java
162. Convert Double To String In Java
163. Deque in Java
164. Converting a List to an Array in Java
165. The Max function in java
166. Removing whitespace from string in java
167. String arrays in Java
168. Strings in Java Vs Strings in Cpp
169. Sum of digits of a number in Java
170. Art of Graphical User Interfaces
171. Trim in Java
172. RxJava
173. Recursion in Java
174. HashSet Java
175. Difference Between Java and Python
176. Square Root in Java
177. Reverse A String in Java
178. Even Odd Program in Java
179. Fibonacci Series in Java
180. Prime Number Program in Java
181. Java Program to Print Prime Numbers in a Given Range
182. Java Leap Year Program
183. Swapping of Two Numbers in Java
184. LCM of Two Numbers in Java
185. Math.sqrt() Function in Java
186. Area of Triangle in Java
187. Sort a String In Java
188. Factorial Program in Java
189. Javafx
190. Lambda expression in java
191. Setup Java Home and IDE on macOS
Organizing code effectively is a key aspect of the programming journey. That's where Packages in Java come into play. Picture them as big folders in your computer holding related files, making them easier to find, manage, and protect. Similarly, Java Packages group together related classes, interfaces, and sub-packages. This makes the code much more manageable and prevents naming conflicts. Also, it promotes code reusability, a key principle of efficient software development.
Packages in Java are like neatly arranged containers for your code. They hold and organize related classes and interfaces in Java, making navigating through the complexities of your code easier. It helps in maintaining your codebase.
Packages in Java are characterized by their ability to prevent naming conflicts and control access to classes and interfaces. They provide a layered structure for your applications, which promotes code modularity and reusability. Effective use of the packages helps to design a well-structured, efficient software system.
Important characteristics of Java packages are:
1. Code Organization
Java packages are used for code organization. They bundle related classes and interfaces into packages.
2. Namespace Management
Each package in Java creates a new namespace, which helps avoid name conflicts. Two classes in different packages can share the same name without conflict because the package name forms part of the class's full name.
3. Access Control
By using access modifiers like public, private, protected, and default, you can control the visibility and accessibility of your classes, interfaces, and their members.
4. Code Reusability
Since related classes and interfaces are organized into packages, they can be reused easily across different parts of an application or even across dissimilar applications.
5. Ease of Distribution
Packages help in bundling related classes and interfaces together into a single distributable unit (like a JAR file), which is useful while dispensing your application.
6. Built-In and User-Defined
Java comes with many built-in packages like java.util, java.io, java.math, etc., which provide a vast array of ready-to-use classes and interfaces. However, you can also define your own packages to suit the requirements of your application.
7. Hierarchical Structure
Packages in Java are hierarchical, meaning one can contain other packages, forming a directory-like structure. This structure is reflected in their naming convention.
Declaring a package is simple. The package ‘keyword’ is used for creating a new package in Java. It should be the first line of code in your Java file. Here's the general syntax:
package packageName;
Defining a package involves creating the Java classes within that. Here's an example:
Package myPackage ;
public class MyC1ass {
// Your code goes here
}
Here, ‘myPackage’ is the package name, and ‘MyClass’ is a Java class that belongs to ‘myPackage’.
Java has some widely accepted rules for naming packages to ensure consistency and avoid conflicts:
1. Lowercase letters
Package names should be in lowercase to avoid conflict with class names and interfaces.
2. Unique names
To avoid conflicts, use unique package names. A common practice is to use the reverse of your domain name, as these are distinctive.
3. No keywords
Java keywords should not be used as package names.
For example, if your website is ‘www.mywebsite.com’, a good package name could be ‘com.mywebsite.mypackage’.
Packages in Java help with the following:
1. Prevent naming conflicts
Packages allow classes to be grouped together. This means you can use the same class name in different packages without causing a naming conflict.
2. Improve readability and organization
By grouping related classes together in packages, your code becomes easier to navigate and understand.
3. Control access
Packages can control access to classes and class members. Java has a number of access modifiers (public, protected, no modifier, and private) that determine the visibility of classes and class members. For instance, class members marked as 'public' are accessible from any other class, while those marked as 'private' can only be approached from within the same class.
Let's consider an example. Assume you're building a library management system. You can have a package for each major feature like this:
package com.library.users;
public class User {
// User-related code
}
package com.library.books;
public class Book {
// Book-related code
}
This code has two packages: ‘com.library.users’ and ‘com.library.books’. The ‘User’ class is in the ‘users’ package, while the ‘Book’ class is in the ‘books’ package.
To use a class from another package, you need to import it. For example, if you want to use the ‘Book’ class in the ‘User’ class, you'd do it like this:
package com.library.users;
import com.library.books.Book;
public class User {
Book myBook;
// Rest of the User code
}
There are two main types of packages in Java:
1. Built-in Packages: Also known as standard packages, these are part of the Java Development Kit (JDK). They come pre-installed with Java and provide a wide range of classes and methods for developers. Examples: java.lang, java.util, java.io, etc.
Here's an illustration of using a class (ArrayList) from the built-in java.util package:
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<>();
list.add("Hello");
list.add("World");
System.out.println(list);
}
}
Output:
2. User-Defined Packages: These are packages created by developers to organize their application's code. You can define yours using the ‘package’ keyword.
For instance, you could create a package com.myapp.shapes and define a Circle class in it:
package com.myapp.shapes;
public class Circle {
// Circle related code
}
To use this Circle class in another package, you would import it like this:
import com.myapp.shapes.Circle;
public class Main {
public static void main(String[] args) {
Circle myCircle = new Circle();
// Rest of the code
}
}
Both built-in and user-defined Java packages are fundamental to keeping your codebase organized and manageable.
Consider the following steps for effective structuring:
1. Categorize Your Code
Identify the distinct functionalities in your application. Each major one could be a separate package.
2. Create Packages
Declare your packages using the package keyword followed by your chosen package name. The package declaration should be the first line of your Java file.
3. Add Classes and Interfaces to Packages
Place related classes and interfaces in the corresponding packages.
For example, if you're building a student management system, you can organize your code like this:
\
package com.myapp.students;
public class Student {
// Student-related code
}
package com.myapp.courses;
public class Course {
// Course-related code
}
Here, com.myapp.students and com.myapp.courses are user-defined packages in Java, holding Student and Course classes, respectively.
Let's highlight the practical usage of packages in Java with example programs.
Example 1: An E-Commerce Application
In an e-commerce application, you can have different modules such as user management, product management, and order management. Each of these can be represented as a package:
// User Management
package com.ecommerce.user;
public class User {
// User-related code
}
// Product Management
package com.ecommerce.product;
public class Product {
// Product-related code
}
// Order Management
package com.ecommerce.order;
public class Order {
// Order-related code
}
2. Example 2: A Banking System
You may have different modules in a banking system, such as account management, loan management, and customer service. Each of these could be a separate package:
// Account Management
package com.bank.account;
public class Account {
// Account-related code
}
// Loan Management
package com.bank.loan;
public class Loan {
// Loan-related code
}
// Customer Service
package com.bank.service;
public class CustomerService {
// CustomerService-related code
}
Example 3: A Library Management System
In a library management system, you may have book management, user management, and loan management modules. Each of these could be a separate package:
// Book Management
package com.library.book;
public class Book {
// Book-related code
}
// User Management
package com.library.user;
public class User {
// User-related code
}
// Loan Management
package com.library.loan;
public class Loan {
// Loan-related code
}
Creating packages in Java is a simple yet essential process for managing your codebase effectively.
Here's a step-by-step guide to developing and managing your Java packages:
To create a package in Java, use the ‘package’ keyword. This declaration should be the first line in your Java file. Here's an example:
packåge com.myapp.shapes;
This line of code creates a package named shapes under the directory com/myapp.
Next, you need to define classes or interfaces within your package. A class is added to a package like this:
package com.myapp.shapes;
public class Circle {
// Circle-related code
}
In this example, a class named Circle is created within the com.myapp.shapes package.
Compile your Java files using javac in your terminal. The command is like this:
javac Circle.java
This will create the ‘Circle.class’ file in the com/myapp/shapes directory.
To use the classes from your package, you have to import them into the Java file where they're needed:
import com.myapp.shapes.Circle;
public class Main {
public static void main(String[] args) {
Circle myCircle = new Circle();
// Rest of the code
}
}
Managing your packages involves organizing your classes into logical units, reusing code across different classes, and ensuring there are no naming conflicts.
Java's static import is a feature that allows members (fields and methods) defined in a class as public static to be used in Java code without specifying the class in which the field is defined. This can lead to more readable and less verbose code.
Normally, to access static members, you need to prefix it with the class name like this:
double result = Math.sqrt(25); // Using sqrt method from Math class
But with static import, you can import the ‘sqrt’ method once and use it directly in your code:
import static java.lang.Math.sqrt;
public class Main {
public static void main(String[] args) {
double result = sqrt(25); // Directly using sqrt without prefixing Math
System.out.println(result);
}
}
In the code above, ‘sqrt’ method from ‘java.lang.Math’ is statically imported, and you can use it directly without prefixing it with ‘Math’.
However, caution is required when using static imports as it may reduce readability if overused because it's not clear which class the method or field is coming from. They are generally employed for frequently used static methods, like those from ‘java.lang.Math’.
This mechanism of importing packages in Java makes your code more readable and reduces verbosity.
Consider we have two packages, ‘com.myapp.shapes’ and ‘com.myapp.main’. In the ‘shapes’, we have a ‘Circle’ class:
// File: com/myapp/shapes/Circle.java
package com.myapp.shapes;
public class Circle {
private double radius;
public Circle(double radius) {
this.radius = radius;
}
public double getArea() {
return Math.PI * radius * radius;
}
}
Now, if we want to use this ‘Circle’ class in our ‘Main’ class, which is in a different package (com.myapp.main), we need to import it:
// File: com/myapp/main/Main.java
package com.myapp.main;
import com.myapp.shapes.Circle; // Importing the Circle class from shapes package
public class Main {
public static void main(String[] args) {
Circle myCircle = new Circle(5.0);
System.out.println("The area of the circle is: " + myCircle.getArea());
}
}
In this example, ‘com.myapp.shapes.Circle’ is imported into the ‘Main’ class. This allows us to create instances of the ‘Circle’ class in ‘Main’. The ‘import’ statement allows the JVM to locate and use the ‘Circle’ class in the ‘Main’ class.
The output of the above code is:
This value is the result of the formula π*r² (pi times the radius squared), which calculates the area of a circle. For a circle with a radius of 5.0, the area is approximately 78.54 (when rounded to the nearest hundredth).
Accessing packages in Java is a simple process. You need to use the ‘import’ keyword followed by the package name (and class or interface) you want to access. Here's a step-by-step guide:
1. Import the Required Package
In your Java file, use the ‘import’ keyword to import the required package. For example, to import the ‘Scanner’ class from the ‘java.util’ package, you would write:
import java.util.Scanner;
If you want to import all classes within a package, you can use the ‘*’ wildcard:
import java.util.*;
Importing packages in Java does not affect the performance of your program. It's simply a directive for the compiler to locate the classes and interfaces you want to use.
Once you've imported a package, you can use the classes or interfaces from that in your code. For example, after importing the ‘Scanner’ class, you can create an instance of it like this:
Scanner scanner = new Scanner(System.in);
Understanding packages in Java is fundamental to becoming a proficient Java programmer. They help in organizing your code into logical groupings and provide access control mechanisms. They also promote the reusability of code and help prevent naming conflicts. Whether you're working with built-in packages, creating your own, or importing classes and interfaces from packages, these concepts form the backbone of code structure in Java.
1. What does the 'default package' mean in Java?
The default package in Java is a package that has no name. When a class or interface is not associated with any package, it belongs to this.
2. When is the ’default package’ used?
Although the ‘default package’ is convenient for small programs and testing purposes, using it for more significant, professional applications is generally discouraged.
3. How does the access control work in Java packages?
Access control in Java packages is managed through access modifiers (public, private, protected, and default (no modifier)). The 'public' modifier allows a class or class member to be accessible from any other class, while the 'private' restricts access to the same class only.
PAVAN VADAPALLI
Director of Engineering
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upGrad does not grant credit; credits are granted, accepted or transferred at the sole discretion of the relevant educational institution offering the diploma or degree. We advise you to enquire further regarding the suitability of this program for your academic, professional requirements and job prospects before enr...