DEV Community: Gayathri.R

In java Collection Framework and under the sub interface and Implement classes.

Gayathri.R — Mon, 16 Feb 2026 09:27:48 +0000

Interface Collection
Its under the java.util pakage
its helps storing and processing effciently,This interface is a member of the Java Collections Framework.

The framework had to be high-performance. The implementations for the fundamental collections (dynamic arrays, linked lists, trees, and hashtables) were to be highly efficient.

The framework had to allow different types of collections to work in a similar manner and with a high degree of interoperability.

The framework had to extend and/or adapt a collection easily.

ArrayList

import java.util.*;
public class CollectionsDemo {

public static void main(String[] args) {
// ArrayList
List a1 = new ArrayList();
a1.add("Zara");
a1.add("Mahnaz");
a1.add("Ayan");
System.out.println(" ArrayList Elements");
System.out.print("\t" + a1);

  // LinkedList
  List l1 = new LinkedList();
  l1.add("Zara");
  l1.add("Mahnaz");
  l1.add("Ayan");
  System.out.println();
  System.out.println(" LinkedList Elements");
  System.out.print("\t" + l1);

  // HashSet
  Set s1 = new HashSet(); 
  s1.add("Zara");
  s1.add("Mahnaz");
  s1.add("Ayan");
  System.out.println();
  System.out.println(" Set Elements");
  System.out.print("\t" + s1);

  // HashMap
  Map m1 = new HashMap(); 
  m1.put("Zara", "8");
  m1.put("Mahnaz", "31");
  m1.put("Ayan", "12");
  m1.put("Daisy", "14");
  System.out.println();
  System.out.println(" Map Elements");
  System.out.print("\t" + m1);

}
}
Set Interface
A Set is a Collection that cannot contain duplicate elements. It models the mathematical set abstraction.

The Set interface contains only methods inherited from Collection and adds the restriction that duplicate elements are prohibited.

Set also adds a stronger contract on the behavior of the equals and hashCode operations, allowing Set instances to be compared meaningfully even if their implementation types differ.

Set has its implementation in various classes like HashSet, TreeSet, LinkedHashSet. Below are some of the implementations of the Set interface in Java.

import java.util.HashSet;
import java.util.Set;

public class SetDemo {

  public static void main(String args[]) { 
      int count[] = {34, 22,10,60,30,22};
      Set<Integer> set = new HashSet<>();
      try {
         for(int i = 0; i < 5; i++) {
            set.add(count[i]);
         }
         System.out.println(set);
      }
      catch(Exception e) {}
   }
}

TreeSet

import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;

public class SetDemo {

  public static void main(String args[]) { 
      int count[] = {34, 22,10,60,30,22};
      Set<Integer> set = new HashSet<>();
      try {
         for(int i = 0; i < 5; i++) {
            set.add(count[i]);
         }
         System.out.println(set);

         TreeSet<Integer> sortedSet = new TreeSet<>(set);
         System.out.println("The sorted list is:");
         System.out.println(sortedSet);

         System.out.println("The First element of the set is: "+ (Integer)sortedSet.first());
         System.out.println("The last element of the set is: "+ (Integer)sortedSet.last());
      }
      catch(Exception e) {}
   }
}

** Map Interface**

The Map interface maps unique keys to values. A key is an object that you use to retrieve a value at a later date.

Given a key and a value, you can store the value in a Map object. After the value is stored, you can retrieve it by using its key.

Several methods throw a NoSuchElementException when no items exist in the invoking map.

A ClassCastException is thrown when an object is incompatible with the elements in a map.

A NullPointerException is thrown if an attempt is made to use a null object and null is not allowed in the map.

An UnsupportedOperationException is thrown when an attempt is made to change an unmodifiable map.


import java.util.HashMap;
import java.util.Map;
public class CollectionsDemo {

   public static void main(String[] args) {
      Map<String, String> m1 = new HashMap<>(); 
      m1.put("Zara", "8");
      m1.put("Mahnaz", "31");
      m1.put("Ayan", "12");
      m1.put("Daisy", "14");

      System.out.println();
      System.out.println(" Map Elements");
      System.out.print("\t" + m1);
   }
}

what is Stream

Gayathri.R — Tue, 20 Jan 2026 10:40:27 +0000

A stream can be defined as a sequence of data. There are two kinds of Streams −

InPutStream − The InputStream is used to read data from a source.

OutPutStream − The OutputStream is used for writing data to a destination.

Streams

Java provides strong but flexible support for I/O related to files and networks but this tutorial covers very basic functionality related to streams and I/O. We will see the most commonly used examples one by one −

what is file handling in java

Gayathri.R — Tue, 20 Jan 2026 10:39:50 +0000

File handling in Java through the java.io package and the java.nio.file package. The main operations covered are creating, reading, writing, and deleting files and directories.

Key Concepts in Java File Handling
Java uses the concept of streams to perform input/output (I/O) operations.

Byte Streams: Used for handling raw binary data (like images, audio). Key classes include FileInputStream and FileOutputStream.
Character Streams: Used for handling text data (16-bit Unicode characters). Key classes include FileReader and FileWriter, often wrapped in BufferedReader and BufferedWriter for efficiency.

The primary class for managing file and directory paths and metadata is the File class.
Core File Operations
Tutorials Point details the following common file operations:

Creating a File: Use the createNewFile() method of the File class to atomically create a new empty file.
Writing to a File: Use classes like FileWriter or FileOutputStream to write data. The BufferedWriter class is often used for buffered, efficient writing of character streams.
Reading from a File: Use classes like FileReader, FileInputStream, or the Scanner class to read data. BufferedReader provides an efficient readLine() method for reading text files line by line.
Deleting a File: Use the delete() method of the File class.
Handling Directories: The File object can also be used to create directories with mkdir() and mkdirs(), and list the files within a directory using list().

Exception Handling
File operations often involve potential errors (e.g., file not found, permission issues), so proper exception handling is essential. The main exceptions to handle are IOException and FileNotFoundException. Using the try-with-resources statement (introduced in Java 7) is the recommended best practice, as it automatically closes resources like streams, preventing leaks.
For detailed examples and tutorials, you can refer directly

what is collection in java

Gayathri.R — Tue, 20 Jan 2026 10:37:14 +0000

What Is a Collections Framework

A collections framework is a unified architecture for representing and manipulating collections. All collections frameworks contain the following

Interfaces: These are abstract data types that represent collections. Interfaces allow collections to be manipulated independently of the details of their representation. In object-oriented languages, interfaces generally form a hierarchy.
Implementations: These are the concrete implementations of the collection interfaces. In essence, they are reusable data structures.
Algorithms: These are the methods that perform useful computations, such as searching and sorting, on objects that implement collection interfaces. The algorithms are said to be polymorphic: that is, the same method can be used on many different implementations of the appropriate collection interface. In essence, algorithms are reusable functionality.

Apart from the Java Collections Framework, the best-known examples of collections frameworks are the C++ Standard Template Library (STL) and Smalltalk's collection hierarchy. Historically, collections frameworks have been quite complex, which gave them a reputation for having a steep learning curve. We believe that the Java Collections Framework breaks with this tradition, as you will learn for yourself in this chapter.

collection in java

Gayathri.R — Wed, 07 Jan 2026 07:32:13 +0000

What Is a Collections Framework?
A collections framework is a unified architecture for representing and manipulating collections. All collections frameworks contain the following:

Interfaces: These are abstract data types that represent collections. Interfaces allow collections to be manipulated independently of the details of their representation. In object-oriented languages, interfaces generally form a hierarchy.
Implementations: These are the concrete implementations of the collection interfaces. In essence, they are reusable data structures.
Algorithms: These are the methods that perform useful computations, such as searching and sorting, on objects that implement collection interfaces. The algorithms are said to be polymorphic: that is, the same method can be used on many different implementations of the appropriate collection interface. In essence,

algorithms are reusable functionality.

Reduces programming effort: By providing useful data structures and algorithms, the Collections Framework frees you to concentrate on the important parts of your program rather than on the low-level "plumbing" required to make it work. By facilitating interoperability among unrelated APIs, the Java Collections Framework frees you from writing adapter objects or conversion code to connect APIs.
Increases program speed and quality: This Collections Framework provides high-performance, high-quality implementations of useful data structures and algorithms. The various implementations of each interface are interchangeable, so programs can be easily tuned by switching collection implementations. Because you're freed from the drudgery of writing your own data structures, you'll have more time to devote to improving programs' quality and performance.
Allows interoperability among unrelated APIs: The collection interfaces are the vernacular by which APIs pass collections back and forth. If my network administration API furnishes a collection of node names and if your GUI toolkit expects a collection of column headings, our APIs will interoperate seamlessly, even though they were written independently.
Reduces effort to learn and to use new APIs: Many APIs naturally take collections on input and furnish them as output. In the past, each such API had a small sub-API devoted to manipulating its collections. There was little consistency among these ad hoc collections sub-APIs, so you had to learn each one from scratch, and it was easy to make mistakes when using them. With the advent of standard collection interfaces, the problem went away.
Reduces effort to design new APIs: This is the flip side of the previous advantage. Designers and implementers don't have to reinvent the wheel each time they create an API that relies on collections; instead, they can use standard collection interfaces.
Fosters software reuse: New data structures that conform to the standard collection interfaces are by nature reusable. The same goes for new algorithms that operate on objects that implement these interfaces.

« Previous • Trail • Next »

what are class in java

Gayathri.R — Wed, 07 Jan 2026 07:10:27 +0000

SYntax
class ClassName {
// variables
// methods
}
example of class
class Student {
int id;
String name;

void display() {
    System.out.println(id + " " + name);
}

}
Types of Classes in Java

Concrete Class

A normal class with full method implementations.

class Car {
    void run() {
        System.out.println("Car is running");
    }
}

Abstract Class

**Declared using abstract

Can have abstract methods and normal methods

Cannot create objects directly

abstract class Animal {
    abstract void sound();
}
abstract class Animal {
    abstract void sound();
}

Interface

Uses interface keyword

Only abstract methods (before Java 8)

Supports multiple inheritance

interface Vehicle {
    void move();
}

Final Class

Cannot be inherited

final class Bank {
    void rate() {
        System.out.println("Fixed rate");
    }
}

Nested Class

A class inside another class.

class Outer {
    class Inner {
        void show() {
            System.out.println("Inner class");
        }
    }
}

Anonymous Class

Class without a name, used for one-time use.

Runnable r = new Runnable() {
    public void run() {
        System.out.println("Running");
    }
};

POJO Class

Plain Old Java Object

No inheritance

Private variables

Public getters/setters

class Employee {
    private int id;

    public int getId() {
        return id;
    }
}

what are the key words in java

Gayathri.R — Fri, 12 Dec 2025 13:23:49 +0000

key words can`t be using as identifiers in your program.the key word const and goto are reserved,even thougth they are not currently used.true,false,null these key words are seem like a keywods but they are actualy literals.

example keywords
abstract
arssert
boolean
byte
break
class
catch
case
char
const
continue
default
float
int
import
implements
interface
long
native
new
private
protected
public
static
this
try
throw
throws
void
voltalite
while
abstract
assert
boolean
break
class

This keyword in java

Gayathri.R — Sat, 11 Oct 2025 06:50:07 +0000

The this keyword refers to the current object in a method or constructor.

The most common use of the this keyword is to eliminate the confusion between class attributes and parameters with the same name (because a class attribute is shadowed by a method or constructor parameter). If you omit the keyword in the example above, the output would be "0" instead of "5".

this can also be used to:

Invoke current class constructor
Invoke current class method
Return the current class object
Pass an argument in the method call
Pass an argument in the constructor call

Object in java

Gayathri.R — Sat, 11 Oct 2025 06:47:10 +0000

An Object is a variable that can hold many variables.

Objects are collections of key-value pairs, where each key (known as property names) has a value.

classname objectvariable=newkeyword classname();

Objects can describe anything like houses, cars, people, animals, or any other subjects.

Method in Java

Gayathri.R — Sat, 11 Oct 2025 06:46:13 +0000

A method is a block of code which only runs when it is called.

You can pass data, known as parameters, into a method.

Methods are used to perform certain actions, and they are also known as functions.

Why use methods? To reuse code: define the code once, and use it many times.

what is variable

Gayathri.R — Wed, 01 Oct 2025 05:15:21 +0000

variables are containers used for storing data values. They are categorized into different types based on the kind of data they hold.
Types of Variables:

String: Stores text, enclosed in double quotes (e.g., "Hello").
int: Stores whole numbers (integers), without decimals (e.g., 123, -123).
float: Stores floating-point numbers (numbers with decimals), requiring an f suffix (e.g., 19.99f, -19.99f).
char: Stores single characters, enclosed in single quotes (e.g., 'a', 'B').
boolean: Stores values with two states: true or false.

Declaring and Assigning Variables:
To create a variable, you must specify its data type and assign it a value using the following syntax:
Java

type variableName = value;

Examples:
string.
Java

String name = "John";

int.
Java

int myNum = 15;

Java Architecture

Gayathri.R — Tue, 30 Sep 2025 15:45:06 +0000

Java architecture usually refers to the structure and design of how Java applications run.

Example: Java Architecture includes JVM (Java Virtual Machine), JRE (Java Runtime Environment), and JDK (Java Development Kit).

It can also mean software architecture (like MVC, layered architecture, microservices, etc.) built using Java.