Java Tutorial

Java Tutorial Java Features C++ vs Java Java History Java Hello World Java Development Kit Java Runtime Environment Java Virtual Machine Difference between JDK, JRE, and JVM Memory Areas in Java Java Operators Java Keywords Primitive Data Types Variables

Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java How to run Java program in command prompt How to run Java program in Eclipse

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java BufferedWriter Java InputStreamReader Java File Java Read File Line By Line Java FileOutputStream Jar File in Java

Serialization

Java Serialization Java transient

Networking

Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket

AWT

Java AWT

Swing

Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java

Java JDBC

Java JDBC Tutorial

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to achieve abstraction in Java How to call static method in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Misc

Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to calculate time difference in Java How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java

Package Program in Java

Package Program in Java

The package program in Java helps us to understand the significance of packages in Java. Packages are mainly used to group together similar classes, interfaces and sub-packages. Package programs in Java are the best examples of data hiding (or data encapsulation). There are two types of packages in Java namely pre-defined/ Build-in packages and user-defined packages.

Pre-defined/ Built-in Packages in Java

Built-in packages are those packages that are comes with JDK. We have to include it in our code and use it. Some of the pre-defined packages are:

  • java.util: We use this package whenever we want to use data structures like Dictionary, LinkedList and assistance for Time and Date operation.

  • java.io: It is used to perform input-output operations.
  • java.net: For networking, we use java.net package.

  • java.lang: This is the package that is imported automatically. This package contains the classes that define math operations, primitive data types like int, float etc. System class is defined in this package.

Sub-Packages in Java

Sub-packages are those packages that reside inside a package. We have to import a sub-package explicitly as the automatic import feature does not come with a sub-package.

Let us observe the following code for a better understanding of the above concepts.

Filename: PackageExample.java

// Importing all classes of util package
import java.util.*;
public class PackageExample
{             
public static void main(String argvs[])
{
               Vector v = new Vector(); // Creating an object of class Vector.
               LinkedList ll = new LinkedList(); // Creating an object of class LinkedList.
               System.out.println("We are learning about Java-package.");  
}
}

Output:

We are learning about Java-package.

Explanation: As we have imported all classes of the java.util package, therefore, we have created objects of Vector and LinkedList class. However, the util package is not only confined to these two classes. It contains a lot of other classes, too, which we have imported and not used in our code. That is why this type of import is generally avoided. We must import only those classes which we are going to use in our code. Thus, the first line of code can be replaced by the following:

import.java.util.Vector;
import.java.util.LinkedList;

Here, we are only loading Vector and LinkedList class, which a good practice. Please note that the util is a package that resides inside the java package. Hence, we can say the util is a sub-package. Since java.lang package is already imported. Therefore, the statement System.out.println(); always works.

We can also re-write the above program to generate the same output.

Filename: PackageExample1.java

public class PackageExample1
{             
public static void main(String argvs[])
{
               // Providing package details along-with class name
               java.util.Vector v = new java.util.Vector(); // Creating an object of class Vector.
               java.util.LinkedList ll = new java.util.LinkedList(); // Creating an object of class
               // LinkedList.
               System.out.println("We are learning about Java-package.");  
}
}

Output:

We are learning about Java-package.

Explanation: Since we have not used the import statements. Therefore, we have to provide every package detail along-with the class name.

The Static Import

Static import is the unique feature applicable for Java 5 (or above). This type of import allows the methods and fields present in a class as public static to be used in the Java code. The following example demonstrates the same.

Filename: PackageExample2.java

// static keyword is important in static import
import static java.lang.System.*;
public class PackageExample2
{             
public static void main(String argvs[])
{
               // No need for the System class here.
               out.println("We are learning about static import.");
}
}

Output:

We are learning about static import.

Explanation: Since out is a static and public member of the System class, and we have already done a static import on the System class. Therefore, we can omit the word System in the code.

User-Defined Package in Java

The packages that are defined by the user are known as user-defined packages. The first step is to create a directory of any name of one’s choice. In our case, we will use the name firstPackage. Inside the firstPackage directory, we create a .java file called BasicPrograms.java.

Package Program in Java

Filename: BasicPrograms.java

// The package name must match the name of the directory.

package firstPackage;
public class BasicPrograms
{             
               // A method for printing names passed in its argument.
               public void printNames(String str)
               {       
                               System.out.print(str);       
               }
}

Outside the firstPackage directory, we create another .java file, namely PackageExample3.java.

Package Program in Java

Filename: PackageExample3.java

// Importing class BasicPrograms by using package firstPackage.
import firstPackage.BasicPrograms;
public class PackageExample3
{
               public static void main(String[] args)
                {
                               // Creating object of BasicPrograms class
                               BasicPrograms obj = new BasicPrograms();
                               // Calling method printNames()
                               obj.printNames("Tutorial And Example");
               }
}

Now, compile the PackageExample3.java file using javac PackageExample3.java and execute it using java PackageExample3. We will get the following output.

Output:

Tutorial And Example

Explanation: The visibility of the class BasicPrograms will be maximized as we are using public access specifier. The same goes for the method printNames(). Therefore, we can easily create an object of BasicPrograms and invoke the method printNames(). But for that to work, we must import BasicNames class, which is achieved with the help of the firstPackage.



ADVERTISEMENT
ADVERTISEMENT